This PDF file contains the errata for “JPE Vol. 1 Issue 1 Paper 3567200” for JPE Vol. 1 Issue 1

This PDF file contains the errata for “JPE Vol. 1 Issue 1 Paper 3567199” for JPE Vol. 1 Issue 1

This PDF file contains the errata for “JPE Vol. 1 Issue 1 Paper 3565206” for JPE Vol. 1 Issue 1

This PDF file contains the errata for “JPE Vol. 1 Issue 1 Paper 3606391” for JPE Vol. 1 Issue 1

The organic light-emitting diode (OLED) has promising applications in flat-panel displays and novel light sources. Thus far, OLED structures have mostly been made by thermal evaporation in vacuum. An alternative approach is to use small molecules that form amorphous (glassy) structures from solutions. Such compounds can be used in ink-jet printing technologies and result in reduced OLED prices. We present an original red fluorescent organic compo-und 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-methyl-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK1), and its derivative 2-(2,6-bis(4-(bis(2-(trityloxy)ethyl) amino)styryl)-4H-pyran-4-ylidene)-1H-indene-1,3(2H)-dione (ZWK2), where the methyl group is replaced with a 4-substituted-styryl group. This change could improve the formation of glassy structures. The thickness of the electroluminescent layer in the device is optimized to the higher power efficiency and obtains: ITO/PEDOT:PSS (40 nm)/ZWK1 (95 nm)/LiF (1 nm)/Al (100 nm), and ITO/PEDOT:PSS (40 nm)/ZWK2 (85 nm)/LiF (1 nm)/Al (100 nm). The maximum of electroluminescence (EL) spectra for the device with the ZWK1 compound is 667 nm, which corresponds to the CIE coordinates x = 0.65 and y = 0.34. The power and luminance efficiency at a luminance of 100 cd/m² is 0.63 lm/W and 1.78 cd/A, respectively. Adding an additional 4-substituted-styryl group to the ZWK1 molecule shifts the maximum of EL spectra to the red region (705 nm) and decreases the efficiencies by one order.

We demonstrate enhanced light extraction in organic light-emitting devices (OLEDs) by using microlens arrays fabricated by a soft lithography technique. A large-area and close-packed polystyrene (PS) monolayer was formed on the SiO₂ substrate using a convective-capillary assembly method, and a polydimethylsiloxane polymer was used to obtain a concave template, from which microlens arrays were fabricated from a photopolymerizable transparent optical adhesive. The microlens contact angle and array fill factor both depend on the size of PS microspheres, and nearly close-packed, hemispherical microlens arrays with microlens contact angle of (85 ± 5 deg) and array fill factor of (85 ± 3)% were obtained with 100-μm PS microspheres. The enhancement in the light-extraction efficiency in OLEDs when such fabricated microlens arrays were attached to the light-emitting surface depends on the contact angle of microlens, device size, and detailed multilayer structure of the OLED. For a large-area (12 × 12 mm) fluorescent OLED with a near close-packed hemispherical microlens array, a maximum enhancement of (70 ± 7)% in the light-extraction efficiency was achieved.

Polymer light-emitting devices based on the in situ formation of a p-i-n junction in a polymer blend have been fabricated by roll lamination. Single-walled carbon nanotubes are used as both the anode and cathode for a fabrication process that does not employ vacuum. The metal-free, thin-film devices exhibit a low turn-on voltage, modestly high efficiency, and brightness. The devices are fairly transparent and exhibit high mechanical flexibility. No failure was observed after repeated bending to a 2.5 mm radius and unbending for 50 cycles. Tandem light-emitting devices were prepared, by stacking a blue device on top of a yellow device, for the convenient generation of various mixed colors.

Organic light-emitting diodes (OLEDs) usually exhibit a low light-outcoupling efficiency of only 20%. Typically, more than 30% of the available power is lost to surface plasmons (SPs). Consequently, the overall efficiency could be strongly enhanced by recovering SP losses. Therefore, three suitable techniques for extracting SPs-index coupling, prism coupling, and grating coupling-are discussed from a theoretical point of view and investigated experimentally in simplified OLED-like structures. The basic physical processes are clarified by systematic variations of the involved layer thicknesses and by excited state lifetime measurements. In addition, the analysis of the results is supported by optical simulations based on a dipole model. Finally, the advantages and disadvantages of each method, their potential efficiency for recovering SP losses, as well as the applicability in OLEDs are compared.

We demonstrate the importance of a comprehensive modeling of the dynamics of excited states in organic optoelectronics devices. Our numerical analysis demonstrates that exciton distributions extracted from spectral emission measurements of OLEDs are equivalent to those obtained by solving charge and exciton transport equations when the position-dependent coupling to optical modes is taken into account. The transport simulations are based on the extended Gaussian disorder model for organic semiconductors. Further, we show that the same numerical modeling framework can be used to accurately simulate bulk-heterojunction organic solar cells with dissociation of charge-transfer excitons. The simulations are compared to experimental data.

We focus on the determination of the internal luminescence quantum efficiency of a green-emitting organic light-emitting diode (OLED). By considering different geometrical configurations of OLED thin-film stacks, we elucidate the role of the internal luminescence quantum efficiency of the emitter in the thin-film microcavity. Combining optical simulations with experimental results, a comprehensive efficiency analysis is performed. Here the electroluminescence of a set of OLEDs is characterized. Additionally, the devices are characterized using time-resolved photoluminescence measurements. The experimental data are analyzed using optical simulations. This analysis leads to a quantification of internal luminescence quantum efficiency and allows conclusions about competing mechanisms resulting in nonradiative recombination of charge carriers.

We report the photophysical characterization, computational results, and device properties for ambipolar phosphine oxide-based host materials that were chemically functionalized to control the charge transport. We study the effects of structural modifications of phosphine oxide hosts on the charge balance in the emissive zone of organic light-emitting devices (OLEDs). Significant changes in charge transport within the emissive layer are observed upon introduction of functional groups, such as pyridine and carbazole, into the organic phosphine oxide host structure. We demonstrate that rational design of host materials allows for the control of charge balance in the emissive zone of OLEDs.

We report an alternative, high-yielding synthesis for the known compound 2,4,6-tris(2′,4′-difluoro-[1,1′-biphenyl]-4-yl)-1,3,5-triazine (tris-(dFB)Tz). The energy of the lowest unoccupied molecular orbital (ELUMO) for tris-(dFB)Tz is estimated to be −3.5 eV from electrochemical measurements. The deep E_LUMO of tris-(dFB)Tz affords a material with excellent electron acceptor characteristics for use in n-doped electron transport layers. Tris-(dFB)Tz shows a four order of magnitude increase in the number of carriers on doping with 8 wt. % Cs₂CO₃. Enhanced electron injection was also observed on doping with Cs₂CO₃, which eliminated the necessity for a separate LiF electron injection layer. Blue phosphorescent organic light-emitting devices (OLEDs) were fabricated using n-doped tris-(dFB)Tz electron transport layers. OLEDs with thick (700-Å) Cs₂CO₃-doped tris-(dFB)Tz electron transport layers had lower operating voltages than OLEDS with an undoped electron transport layer of bis(diphenylphosphoryl)dibenzothiophene (PO15), which has previously been used in low-voltage, high-efficiency OLEDs. The tris-(dFB)Tz results indicate that aromatic substituted triazines may be promising materials for use as electron acceptors in n-doped organic electronic systems.

For organic light-emitting-diode (OLED) lighting to be successful, it is critical that it be properly positioned in the marketplace. It is also critical that both the performance and cost be competitive against other lighting technologies in the selected marketplace. This presentation gives an overview of OLED lighting technology from these perspectives. It shows that OLED lighting products should be positioned as luminaires and not light bulbs, which affects both the performance and price expectations. Laboratory OLED devices already demonstrated efficacies that are more than competitive against luminaires based on other lighting technologies. There is potential for substantial further improvement in efficacy. The greatest opportunities come from light-extraction efficiency improvements and from an improved blue emitting system. There has been great recent progress in the OLED device lifetime. To be acceptable as luminaires, however, OLED may need even more lifetime improvements. Not all the improvements need to come from OLED technology improvement, however. We discuss other means to effectively improve the lifetime of OLED lighting panels and show why there is optimism that, with volume production, OLED lighting can be competitive against other luminaires even on the first-cost basis.

A numerical self-consisted dynamic model of a silicon evanescent laser is presented. This model allows us to calculate the laser output power as a function of drive current and mode composition. Obtained results are in good agreement with published experimental data. Dynamic processes in silicon evanescent lasers are also investigated, and self-modulation processes are observed.

We describe how to use the thin-film transistor (TFT) technique to quantify carrier transport of amorphous organic semiconductors relevant to organic electronic devices. We have chosen several amorphous materials, including arylamine compounds, 4,4′-N,N′-dicarbazole-biphenyl (CBP), and a phosphorescent dye molecule [Ir(ppy)₃] for investigations. Generally, the field effect (FE) mobility was found to be about one order of magnitude smaller than that obtained from an independent time-of-flight (TOF) technique. For N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) and N,N′-Bis(3-methylphenyl)-N,N′-bis(phenyl)-9,9-spirobifluorene (spiro-TPD), the FE mobilities were found to be 1.7×10−⁵ and 1.3 ×10−⁵cm²/Vs, respectively. Temperature-dependent measurements were carried out to study the FE mobility. It was found that the energetic disorder increased in the neighborhood of a gate dielectric layer. This factor is one of the origins causing the discrepancy between TFT and TOF mobilities. We also examined how the hole transport of CBP is affected by Ir(ppy)3 when it is doped into CBP.

We investigated guided mode extraction in organic light-emitting diodes and compare the experimental findings to transfer matrix (T-matrix) and finite difference time domain (FDTD) simulations. To this end, we patterned the indium tin oxide anode with Bragg gratings with lattice constants from 300 to 600 nm and varied the depth of the grating structures. The structuring was done by laser interference lithography and plasma etching. Both techniques allow for a rapid large area processing. We measured angle resolved electroluminescent spectra of the nanostructured devices and reference devices. To obtain the mode distribution in the devices we made use of T-matrix simulations. In addition we performed FDTD simulations of the emission characteristics of the patterned devices. The simulations are in agreement with our experimental findings and give insight into the outcoupling mechanisms.

Organic light-emitting diodes (OLEDs) are a key technology in solid state lighting. Without a long-lived phosphorescent blue emitter, a hybrid concept based on phosphorescent red and green emitters and a fluorescent blue emitter in a white OLED stack is a promising approach for pure-white emission. Several challenges such as exciton recombination on all emitters and triplet diffusion, as well as quenching, have to be overcome. To address these issues, a mixed-host phosphorescent emission layer is employed. The mixture ratio is locally varied in the emission layer. An interlayer separates the phosphorescent and fluorescent emission layer. Strategies to tune the color coordinates are presented. The lifetime and color stability versus luminance are investigated. At Commission Internationale de I'Eclairage color coordinates of 0.44/0.44, a current efficacy of 28.0 cd/A (at 1000 cd/m²), and a luminous efficacy of 20.6 lm/W can be measured.

In the framework of the one-dimensional mean-field (MF) drift-diffusion approach the well-defined boundary conditions far away from the metal/insulator contacts of a planar metal/insulator/metal system are used to determine the boundary condition at the interface itself. The novel self-consistent boundary condition linking the carrier density and the electric field at the interface enables a straightforward description of the current voltage (IV) characteristics in forward and reverse bias bridging space charge and injection-limited regimes and accounting for barrier lowering from the potential drop in the used contact materials. Yet, because of the low carrier density in the insulator under injection limitation, single-particle phenomena, such as the Schottky effect, must be considered. We reconsider the validity of the MF approach, depending on the external bias and the prevailing injection barriers. For the crucial parameter window where the MF approach fails and single-particle phenomena become important, a modification of the boundary conditions at the insulator/metal interface is proposed to account for the discrete nature of carriers. The difference between the thus modified MF and the unmodified MF approach is illustrated by several examples.

Large-area top-emitting PIN structure (highly p- and n- type doped transport layers for electrons and holes and an undoped emitter layer)-organic light-emitting diode (OLED) on advanced metal foils were fabricated for lighting applications. ArcelorMittal has developed a new surface treatment on metal foils, suitable for roll-to-roll production and dedicated to large-area device integration. Both monochromatic and white devices are realized on advanced metal foils. Power efficiencies at 1000 cd/m² of >70 lm/W (green), moreover, power efficiency of white devices of >22 lm/W are achieved. Furthermore, first large-area 60 × 60 cm white OLED sources on metal foils are presented.

Microcavity tandem organic light-emitting diodes (OLEDs) are simulated and compared to experimental results. The simulations are based on two complementary techniques: rigorous finite element solutions of Maxwell's equations and Fourier space scattering matrix solutions. A narrowing and blue shift of the emission spectrum relative to the noncavity single unit OLED is obtained both theoretically and experimentally. In the simulations, a distribution of emitting sources is placed near the interface of the electron transport layer tris(8-hydroxyquinoline) Al (Alq₃) and the hole transport layer (N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (α-NPB). Far-field electric field intensities are simulated. The simulated widths of the emission peaks also agree with the experimental results. The simulations of the 2-unit tandem OLEDs shifted the emission to shorter wavelength, in agreement with experimental measurements. The emission spectra's dependence on individual layer thicknesses also agreed well with measurements. Approaches to simulate and improve the light emission intensity from these OLEDs, in particular for white OLEDs, are discussed.

Recent electroluminescence (EL) detected magnetic resonance and transient EL studies reveal the presence and role of holes that drift beyond the recombination zone and approach the cathode in small molecular organic light-emitting diodes (OLEDs) with specific materials and structures. In particular, these studies suggest that these holes are responsible for trion (i.e., a bipolaron stabilized by a counterpolaron on an adjacent molecule) formation in the electron transport layer, and may contribute to EL spikes observed at the end of a bias pulse. The significance of these holes to overall OLED performance is discussed.

We report on polymer light-emitting diodes (PLEDs) with embedded SiO2 nanoparticle interlayers. We fabricated PLEDs with a rather thick (180 nm) SiO₂ interlayer between the hole injection layer and a 50-nm thin emission layer. We also made devices, where the interlayer was embedded inside the emission layer. The devices were characterized by electroluminescence and photoluminescence measurements and compared to the respective reference devices. We achieved an enhancement factor of 1.74 for the luminous efficacy and 2.13 for the current efficiency at 4000 cd/m² for the PLED with the interlayer between the hole injection layer and the emission layer compared to the reference device. For PLEDs with the interlayer between the two emission layers, we obtained an enhancement factor of 1.68 for the luminous efficacy and 1.45 for the current efficiency at 4000 cd/m² compared to the corresponding reference device. This surprising enhancement can be explained by a superposition of increased internal quantum efficiency and an increase in the extraction efficiency.

A device structure that enables the combination of phosphorescent green and fluorescent blue emitters in a solution processed polymer organic light-emitting diode device has been developed. Results demonstrate that it is possible to tune the color of emission by appropriate formulation of the polymers that are used. This enabled the development of a warm white device that had CIE coordinates of (0.462, 0.426), and an external quantum efficiency (EQE) of 13.1%. This EQE was limited by the efficiencies of the emitters used rather than through any internal quenching, and thus the device structure offers potential for further development.

Electromodulation spectroscopy has been used to probe the effect of a polymer hole injection layer on electric fields and charge injection in vacuum-deposited organic light-emitting diodes. The electromodulation spectrum consists of electroabsorption of the transport layers and excited state absorption of trapped cations in the hole transport layer. Field-dependent modulation of trapped charge at the interface between the injection and transport layers substantially modifies the electric field distribution within the device. In reverse bias, the electric field strength is suppressed within the hole transport layer and concentrated in the electron transport layer. In forward bias, field-dependent doping of the hole transport layer dominates the electromodulation spectrum. The field-dependent trap density is calculated to be of order 10¹³ cm⁻², equivalent to μC/cm² charge density. The built-in potential is estimated to be between 2.2 and 2.5 V, consistent with low carrier injection barriers.

We demonstrate organic light-emitting diodes (OLEDs) capable of yielding sunlight-style illumination with various daylight chromaticities, whose color temperature (CT) covers those of the daylight at different times and regions. Besides having the disruptive characters like being plane-type and luminaire-ready, flexible, printable, thin, and light, the emissive spectrum of OLEDs closely resembles that of sunlight. The degree of sunlight spectrum resemblance is 63%, for example, for one high color rendering OLED, while 2% for a sodium lamp, 16% for a fluorescent tube, 49% for a light-emitting diode, and 72% for an incandescent bulb. By incorporating one hole-modulating layer (HML), a fluorescent sunlight-style OLED yields CT between 2300 and 7900 K, while the CT span can be further expanded between 2400 and 18000 K by using double HMLs. For a phosphorescent sunlight-style OLED, the CT spans between 1900 and 3100 K with a power efficiency of 17.6 lm/W at 1000 cd/m².

Electrically doped, organic transport layers are important for today's high efficiency organic (opto-)electronic devices. Doped organic layers have a strongly increased free charge carrier density compared to their undoped counterparts and also improve the charge carrier injection from adjacent electrodes into the organics. For practical applications, especially in optoelectronics, these layers have to have low absorption in the wavelength range of interest. The two nearly colorless p- and n-doping materials, rhenium heptoxide and cesium carbonate, are investigated focusing on their conductivity enhancement, injection improvement, and voltage drop over doped transport layers in organic light emitting diodes. They show very good doping properties already at moderate doping concentrations and prove that they can be used in variable thicknesses without a significant voltage increase. This makes them cheap, low absorbing alternatives to today's, well-established doping systems.

The most commonly used transparent electrode, indium-tin oxide (ITO), is costly and requires methods of deposition that are highly destructive to organic materials when it is deposited on top of the organic layers in top-emitting organic light-emitting devices (OLEDs). Here we have employed a trilayer electrode structure consisting of a thin layer of metal sandwiched between two MoO₃ layers, which can be deposited through vacuum thermal evaporation without much damage to the organic active layers. Such MoO₃/Au/MoO₃ trilayer electrodes have a maximum transmittance of nearly 90% at 600 nm and a sheet resistance of <10 ohms per square (Ω/sq) with a 10-nm thick Au intermediate layer. Using these trilayers as the top transparent anode, we have fabricated top-emitting OLEDs based on either a fluorescent or phosphorescent emitter, and observed nearly identical emission spectra and similar external quantum efficiencies as compared to the more conventional bottom-emitting OLEDs based on the commercial ITO anode. The power efficiency of the top-emitting devices is 20% to 30% lower than the bottom-emitting devices due to the somewhat inferior charge injection in the top-emitting devices. The performance and emission characteristics of these devices indicate that this trilayer structure is a promising candidate as a transparent anode in top-emitting OLEDs.

We have investigated how to optimize the efficacy and angle dependence of emission of top-emissive organic light-emitting diodes (OLEDs) based on metal foil substrates with the aim of creating efficient flexible devices for lighting and signage applications. By systematically varying the device architecture we were able to tune the optical microcavity which exists within the device structure and observe the change in performance. We paid particular attention to the effects of the metal foil roughness. We have seen that by changing the layer thickness of the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) [PEDOT:PSS] in the device, and the substrate reflectivity and roughness we can obtain efficacies not too far from those achieved for standard bottom-emissive devices on glass substrates made with the same emitter. The angle dependence of luminance can be tuned from pointing in the forward direction via Lambertian to having a maximum at around 65°, and we have used optical modeling to help us find the optimum device structure. We conclude that (rough) metal foils are a realistic possibility for making flexible OLEDs and have demonstrated large area (up to 12 cm × 12 cm), thin film encapsulated, flexible devices.

White light emitting devices were fabricated using blue emitting organic light emitting diodes (OLEDs) and down-conversion phosphor mixtures. Three different thicknesses of yellow and mixtures of yellow and red luminescent phosphor films were prepared on separate glass slides using a silicone matrix. The down-conversion films were optimized by varying the thickness and phosphor to silicone weight ratio. The phosphor films with different thickness were coupled to an optimized blue emitting OLED with a refractive index matching gel. Optimized down-conversion phosphor layers integrated with blue OLEDs exhibited 2× enhancement of efficiency (lumens per electrical Watt) for white to that of the blue OLED. The International Commission of Illumination color coordinates and average color rendering index for this device were (0.43, 0.46) and >80, respectively.

This PDF file contains the editorial “Guest Editorial: Organic Light-Emitting Materials and Devices” for JPE Vol. 1 Issue 1

We present the in-depth investigation of solution-processed bulk-heterojunction solar cells based on the merocyanine dye MD304 as a donor in combination with the soluble fullerene derivative [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as acceptor. The optimized MD304:PCBM devices exhibit an external quantum efficiency of ca. 50%, and a power conversion efficiency of up to 2.1% under standard illumination and 2.7% under reduced illumination intensities. Because of the strongly dipolar character of merocyanine dyes the bulk material features a relatively large dielectric constant, which is beneficial for charge transport and reduced carrier recombination. This somewhat compensates the limited hole mobility of the dipolar merocyanine.

We investigate the effects of interfacial layers on the photovoltaic properties of bilayer organic heterojunction photovoltaic devices. The devices were fabricated using aluminum phthalocyanine chloride (AlPcCl) as electron donor and fullerene (C₆₀) as electron acceptor. Two types of interfacial layers inserted between the transparent indium-tin-oxide anode and the AlPcCl layer were investigated: PEDOT:PSS and MoO₃. We find that these interfacial layers have a strong influence on the device open-circuit voltage (V_OC). The effects of temperature and illumination intensity on V_OC were explored.

Dye-sensitized solar cells (DSCs) using the p-type semiconductor CuAlO₂, in conjunction with a highly effective hole injecting dye and an iodide-triiodide-based electrolyte have been produced, demonstrating photocathodic behavior. An improved open-circuit voltage (V_oc) of 333 mV was observed, compared to analogous devices using NiO, which can be explained by the CuAlO₂ valence-band energy, which is lower on the vacuum scale than that of NiO. Incident photon-to-charge-carrier efficiency response confirms that the observed photocurrent is generated by the dye.

The work focuses on the degradation of performance induced by both water and oxygen in an inverted geometry organic photovoltaic device with emphasis on the accumulated barrier effect of the layers comprising the layer stack. By studying the exchange of oxygen in the zinc oxide (ZnO) layer, the barrier effect is reported in both a dry oxygen atmosphere and an oxygen-free humid atmosphere. The devices under study are comprised of a bulk heterojunction formed by poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester sandwiched between a layer of zinc oxide (electron transporting layer) and a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (hole transport layer) and the two electrodes indium tin oxide and silver. Time-of-flight secondary ion mass spectrometry is employed to characterize the accumulated barrier effect. A pronounced barrier effect is observed in the humid atmosphere, correlating well with a long observed lifetime in the same atmosphere

We investigate the counterintuitive phenomenon of inserting a transition metal oxide layer to improve hole injection or extraction in organic semiconductor devices using ultraviolet photoemission (UPS), x-ray photoemission (XPS), and inverse photoemission spectroscopy. We observe that metal oxides, such as MoO₃ and WO₃, substantially increase the work function when deposited on indium tin oxide. The increase lifts up the highest occupied molecular orbital (HOMO) of the hole transport layer and therefore reduces the energy barrier between the HOMO and the Fermi level of the anode. The uplift creates an interface band-bending-like region that results in a drift electric field, which encourages the collection of holes at the anode. The optimum thickness for the oxide layer is estimated to be 2 nm. We also investigate the effects of air and O₂ exposure of MoO_x films. We observe that while most of the electronic energy levels of the oxide remain largely intact, the work-function reduction is substantial. The UPS and XPS data indicate that chemisorption is the major contributor of the work-function reduction. The reduction can be seen in two stages: initially dominated by oxygen adsorption at exposure <10¹³ L, and finally saturated by moisture at 10¹⁴ L.

Carboxylic acid functionalized pentacene-based dyes are synthesized and tested in dye-sensitized solar cells utilizing titania (rutile) nanowire arrays as the electron transporting photoanode. Functionalization on both chromophore and solubilizing substitutents leads to materials demonstrating promising light-harvesting and energy-conversion properties in these large polycyclic aromatic compounds.

A thienylsilane molecular layer is self-assembled onto vertically aligned ZnO nanowire templates for promoting in situ electrochemical polymerization of P3HT. The silane functionalization on ZnO surface is investigated using x-ray photoelectron spectroscopy and water contact angle measurements. The silane-based surface modified layer acts as a favorable nucleation site for electrochemical polymerization. We find that the oxidation potential for electrochemical polymerization is obviously decreased compared to that without a surface modifier. The UV-visible absorption in the ZnO nanowire/P3HT film with thienylsilane molecular layer is much stronger than that without surface modification.

The degradation mechanism of pentacene/fullerene (C₆₀)-based photovoltaic device is studied as a function of heating time. The efficiency of the device with bathocuproine (BCP) as buffer layer shows a considerable decay from 1.49 to 0.6% after 168-h heating, whereas the device without BCP possessed a stable performance under heating treatment. This decay is mainly caused by the poor thermal stability of BCP, which crystallized after the heating treatment and is discussed through the incident photon-to-electron conversion efficiency (IPCE) and the atomic force microscopic (AFM) measurements. The IPCE results indicated the redistribution of optical field due to the crystallization of BCP, and the AFM images showed the significant increase in surface root-mean-square value from 0.46 to 24.7 nm. Furthermore, the device without BCP exhibited the decrease in series resistance (R_s). The reduced R_s was attributed to the polycrystallized-like molecular arrangement after heating, which was confirmed by the Gaussian-disordered model.

We report on the electronic structure of freshly evaporated and air-exposed Molybdenum tri-oxide (MoO₃) and the energy-level alignment between this compound and a hole-transport material [e.g., N,N′-diphenyl-N,N′-bis (1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD)]. Ultraviolet and inverse photoelectron spectroscopy show that freshly evaporated MoO3 exhibits deep-lying electronic states with an electron affinity (EA) of 6.7 eV and ionization energy (IE) of 9.7 eV. Air exposure reduces EA and IE by ∼1 eV, to 5.5 and 8.6 eV, respectively, but does not affect the hole-injection efficiency, which is confirmed by device studies. Thus, MoO₃ can be applied in low-vacuum environment, which is particularly important for low-cost manufacturing processes. Our findings of the energy-level alignment between MoO3 and α-NPD also leads to a revised interpretation of the charge-injection mechanism, whereby the hole-injection corresponds to an electron extraction from the organic highest-occupied molecular orbital (HOMO) level via the MoO₃ conduction band.

Fiber and pillar tandem dye-sensitized solar cells (DSCs), which do not need transparent conductive oxideless layer tandem cells (TCO-less TAN), are fabricated and their fundamental tandem properties are evaluated. TCO-less TAN cells consist of a light-splitting waveguide and TCO-less DSCs. The TCO-less DSC is composed of a nanoporous titania back-contacted with a porous Ti electrode or a nanoporous titania sheet supported by a stainless steel mesh whose surface was protected with TiO_x thin layers. Two kinds of light-splitting structures are introduced. One is a light-splitting structure in which polystyrene particles with different diameters are dispersed in water. The other consists of dichroic mirrors. These light-splitting structures are coupled with TCO-less DSCs stained with dyes absorbing light corresponding to these split lights. Open circuit voltages (V_oc) of these TCO-less tandem DSCs are two times (two tandem structure) or three times (three tandem structure) higher than those of the corresponding single cells, demonstrating that these structures work as tandem cells.

Two new conjugated polymers consisting of the donors 1,5-bis(2-hexyldecyloxy)naphthalene, thiophene, or bithiophene and the acceptor benzothiadiazole has been synthesized and their optical and photovoltaic properties have been characterized. The two polymers were compared with earlier synthesized and characterized polymers containing benzene instead of naphthalene. The two polymers absorb light in the visible spectrum (400 to 700 nm). The naphthalene containing polymers had blueshifted absorption spectra compared to the benzene containing polymers and also higher band gaps. In photovoltaic devices the bithiophene containing polymer gave the best efficiency of 0.6%, whereas the single thiophene only showed efficiency of 0.005%. This is lower than the best benzene incorporated polymer that showed efficiency up to 2.2%.

The charge transport properties of organic electronic materials are of critical importance for the understanding of the operation of organic photonic devices. We show in this study that admittance spectroscopy (AS), which is a measure of the frequency dependent capacitances of organic electronic materials, can be used to determine charge carrier mobilities and transport parameters in organic photovoltaic materials. A plot of the negative differential susceptance versus frequency yields a maximum at a frequency. The position of the maximum is related to the average carrier transit time. Using AS, we study the hole transport properties of thin films of poly(3-hexylthiophene) (P3HT) based materials for organic photovoltaic applications, including pristine P3HT, and P3HT doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We demonstrate that AS can be used to extract hole mobilities of P3HT and P3HT:PCBM with a thickness of ∼350 nm. For P3HT:PCBM, copper phthalocyanine is used as an electron trapping layer to reduce the effect of negative capacitance.

The effect of p-type doping of the donor layer with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) on the performance of planar pn-heterojunction organic photovoltaic devices using 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) or 4,4′,4″-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA) as an electron donor and C₆₀ as an electron acceptor was studied. It was found that doping of the donor layer with F₄TCNQ increases both the short-circuit photocurrent and the fill factor by 1.7 to 2.0 times and 1.5 to 1.6 times, respectively, but reduces the open-circuit voltage, resulting in the enhancement of power conversion efficiency by 1.6 to 1.7 times. These features caused by the doping are attributed to the decrease in the bulk resistance of the electron donor layer as a result of the p-type doping. The decrease in the open-circuit voltage was partly compensated by incorporation of a thin layer of undoped m-MTDATA on the ITO electrode, and hence, the power conversion efficiency was further enhanced.

In this contribution the effect of changes in the active material system and modification of contact properties in organic solar cells is investigated at the example of ZnPc:C₆₀ small molecule solar cells. Devices with different blend mixing ratios and a variation of hole transport layer are prepared by vacuum deposition and compared to drift-diffusion simulation data. It is shown that the open circuit voltage is mainly defined by the mixing ratio, whereas the fill factor is strongly influenced by the choice of hole transport layer. Extraction barriers for photogenerated holes lead to S-shaped IV curves. The strength of the S-shape scales with the height of the extraction barrier. The slope of the IV curves at open circuit suggests that the observed increase in open circuit voltage with a higher amount of C₆₀ in the blend might be due to a downshift of the highest occupied molecular orbital of ZnPc.

Organic-inorganic hybrid solar cells with a cell structure of indium tin oxide/TiO₂/TiO_x:hyperbranched phthalocyanine/CuSCN/Au (or carbon) have been fabricated by solution based processing using three hyperbranched phthalocyanines (H₂PPc, TiOPPc and CuPPc) as light-absorbing materials. These organic-inorganic hybrid solar cells are extremely thin absorber solar cells, which possess p-i-n heterojunctions ("i," an intrinsic absorber layer), as they were confirmed by scanning electron microscopy. With an illuminated area of 1 cm², a solar cell made from H₂PPc achieved conversion efficiency of 0.23% under 1-sun air mass 1.5 global illumination. The lower conversion efficiency for the cell made from CuPPc was likely due to the energy loss in the formation of triplet states with an intersystem crossing time of 0.76 ps.

Polyaniline-(PANI)-poly (methyl methacrylate) (PMMA) blend was used to fabricate the Schottky device: Al/ PANI-PMMA /Au. Current density-voltage (J-V) capacitance-voltage (C-V), and complex impedance measurements were used to evaluate the junction parameters of the devices. The photovoltaic parameters of the cells are estimated from the analysis of the current-voltage characteristics under illumination.

The formation of a well-defined, reproducible ZnO nanorod scaffold for hybrid photovoltaic applications has been investigated. A standard hydrothermal growth method was used and the influence of chemical additions in controlling length, width, density, and orientation was studied. The nanostructures prepared have been characterized by scanning electron microscopy, x-ray diffraction, UV-visible spectroscopy in addition to measurement of the wetting behavior. A standard procedure for the production of vertically orientated nanorods with a narrow size distribution, high areal density, and good wettability in aqueous solutions is presented.

Currently, polymer/fullerene solar cells have significantly higher power conversion efficiency than polymer/polymer solar cells. In order to address the origin of this wide gap, we measured the transient absorption spectra of polymer/polymer blend films based on poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), and analyzed the charge generation dynamics in comparison with that of a polymer/fullerene blend film based on P3HT and [6,6]-phenyl-C₆₁ butyric acid methyl ether (PCBM). In P3HT/PCBM blend films, half of the polarons are generated immediately after pulsed laser excitation at the P3HT absorption band and the other half are generated with a rise constant of ∼10 ps. The prompt polaron formation is assigned to the charge generation from P3HT singlet excitons located near the P3HT/PCBM interface and the delayed polaron formation to the charge generation after the exciton migration to the P3HT/PCBM interface. In P3HT/F8BT, on the other hand, F8BT singlet excitons observed immediately after the laser excitation decayed in a picosecond and P3HT singlet excitons increased on the same time constant, suggesting efficient energy transfer from F8BT to P3HT. Polymer polarons were generated on a time scale of ∼40 ps, some of which were observed on a microsecond timescale but the yield was much smaller than that in P3HT/PCBM. We discuss the difference in charge generation dynamics in terms of kinetics and interfacial structures.

The organic semiconductors of poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene)(P3OT), poly(3-dodecylthiophene) (P3DDT) and [6,6]-phenyl C₇₁ butyric acid methyl ester (PC71BM) were used to make active layers. The active layers of an organic thin film solar cell were fabricated by the P3HT/PC71BM, P3HT/P3OT/PC71BM and P3HT/P3DDT/PC71BM fluid, respectively. Compared with the performances, the performance of the organic solar cell fabricated by P3HT/P3OT/PC71BM thin film indicates the best. The open circuit voltage is 0.61 V. The short-circuit current density is 6.55 mA cm². The fill factor is 0.51. The power conversion efficiency is 2.07%.

Cyclopropano[70]fullerenes have been synthesized in the aim of being used as acceptors in blends based on regioregular poly (3,5-Hexylthiophene) RR-P3HT for photovoltaic (PV) plastic cells. These molecules used with RR-P3HT in bulk heterojunction (BHJ) configuration provided interesting characteristics: 1.5% solar conversion efficiency, 9.29 mA/cm² current density, 0.51 V open circuit voltage, and 0.34 fill factor. The IPCE spectrum for P3HT: cyclopropano[70]fullerene cells shows a peak around 430 nm with 71% external quantum efficiency. This result justifies the increased current density.

Absorption enhancement by a double plasmonic nanostructure in molecular organic photovoltaics (OPVs) is theoretically investigated. The structure consists of a periodic array of metal nanodiscs on one side of the OPV active layers and a thin metal nanohole array on the other side. Excitation of coupled modes of localized surface plasmon polaritons at the nanodiscs and short-range surface plasmon polaritons at the nanohole array causes the electromagnetic field to be highly concentrated within the organic active layers, leading to a polarization-independent, broadband absorption enhancement in the visible and near-infrared portion of the solar spectrum. Calculations show that an optimized double plasmonic structure can enhance the total photon absorption by >125% for molecular OPVs based on a double heterojunction of an electron donor/hole transporter and an electron acceptor/transporter.

Most efficient polymer solar cells are usually fabricated from toxic organic solvents, such as chloroform, chlorobenzene, or dichlorobenzene (ODCB). Here, we demonstrate a power conversion efficiency of 4.5% in solar cells with a new blue polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) mixed with PC₇₁BM and processed from mixed solvents of toluene and ODCB in a ratio of 9:1. Decreasing the content of ODCB makes device processing more compatible with the environment for large scale production, with 10% reduction of photocurrent compared to devices from pure ODCB under optimized conditions. In addition, less variation of photocurrent is obtained in solar cells processed from mixed solvents than from pure ODCB due to varying nanostructure in the blends, which is also critical for production.

This study investigated the relationship between the anthocyanin concentration in a series of organic fruit species and the photoelectrochemical performance of the TiO₂ dye-sensitized solar cells (DSSCs) sensitized by these dyes. It was hypothesized that organic dyes with a greater anthocyanin concentration have higher fill factors (FFs) and maximum output power (PMAX), which would lead to higher energy conversion efficiency. Anthocyanin dye solution was extracted from eight test fruits using water as the extracting solvent. Using these test organic dyes, multiple DSSCs were assembled such that light entered through the TiO₂ side of the cell. The full current-voltage (I-V) covariations were measured at various incremental resistance values. Defining PMAX as the dependent variable, a series of linear, semi-logarithmic, quadratic, and finally power law regression models were used to investigate the relationship between anthocyanin concentration and photoelectrochemical performance. Regression analysis demonstrated that the power law model (R² = 0.86) was the best fit and experimentally sound model to predict the relationship between PMAX and anthocyanin concentration. Based on this model, anthocyanin content and PMAX relation approaches zero for zero concentration and follows a sublinear increase for higher concentration. Dyes extracted from blueberry and black raspberry with the highest anthocyanin content generated higher PMAX with better FF and conversion efficiency. Estimating these linear and power law models is the first step in finding organic anthocyanin sources in nature that have the highest dye content to efficiently generate energy.

The correlation between the physical properties of spin-casting solvents, film morphology, nanoscale charge transport, and device performance was studied in poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) blends, spin cast with two halogenated aromatic solvents: chlorobenzene (CB) and ortho-dichlorobenzene (1,2-DCB). 1,2-DCB-based blends exhibited fine phase separation of ∼10 to 15 nm length scale with ordered self-assembly of P3HT whereas blends spin cast from CB showed coarse phase separation with large isolated clusters of ∼25 to 100 nm of donor- and acceptor-rich regions. Higher solubility of both P3HT and PCBM in 1,2-DCB and a slower drying rate of 1,2-DCB (because of higher boiling point) facilitated self-organization and ordering of P3HT and promoted finer phase separation. Higher local hole mobility in 1,2-DCB-based blend was attributed to efficient hole transport through the ordered network of P3HT chains. Moreover, higher local illuminated current (dark + photocurrent) in 1,2-DCB-based blend suggested efficient diffusion and dissociation of excitons due to finer phase separation. As a consequence, 1,2-DCB-based devices exhibited higher short circuit current density (J_sc), external quantum efficiency and power conversion efficiency in contrast to the CB-based device. It was also observed that the device performance was not limited by light absorption and exciton generation; rather morphology dependent processes subsequent to exciton generation, primarily charge transport to the electrodes, limited device performance.

This PDF file contains the editorial “Guest Editorial: Special Section on Organic Photovoltaics” for JPE Vol. 1 Issue 1

Power harvesting is the process of extracting useful electrical energy from ambient low grade energy sources such as solar energy, mechanical energy, and thermal energy using smart materials as transducers. These materials have the ability to convert one form of energy into another. This paper aims at thermal-electrical energy converters based on a pyroelectric effect for energy harvesting, and examines its possible use in ultralow power devices and sensor modules. The present work investigates theoretically the energy harvesting capacity of pyroelectric samples fabricated in our laboratory and commercially available pyroelectric elements/transducers by capturing thermal energy of pavements. The single- and polycrystalline elements: triglycine selenate; lithium tantalate; modified lead zirconate titanate; modified lead titanate; modified lead metaniobate; and pyroelectric polymer nanocomposites such as Portland cement; nanocarbon fibers; polymer-lithium tantalate embedded with silver nanoparticles; and others were characterized for applicable performance parameters. The modeling and numerical simulation of energy harvesting capacity of these samples with the available pavement's temperature-profile data over an extended period of time were investigated. The results indicate that the electrical energy harvesting via pyroelectricity is a feasible technique for powering autonomous low-duty electric devices.Based on our analysis of a single electric-energy harvesting unit, the triglycine selenate elements shall perform better than others with regard to the amount of voltage and energy densities extracted with respect to time. Possible future work and concepts of developing promising multidomain energy harvesters or hybrid harvesters are also briefly discussed.

We address a passive sunlight concentration system containing optical waveguides that connect the optical module with the photovoltaic (PV) cells. We propose to realize pseudorandom structures along the interface between the core and the cladding of the optical waveguide such that different spectral components of the collected sunlight's radiation will be spatially separated. Different types of PV cells with engineered bandgaps are used for each such spatial region and, by that, improve the energetic efficiency at which the photons are converted into electrons.

Size- and structure-dependent efficiency enhancement methods are studied for luminescent solar concentrators (LSCs) fabricated by casting organic laser dyes into PMMA matrixes. The enhancement are achieved mainly by attaching a white diffuser with an airgap at the bottom of the LSC and adding refractive index matched optical gel between the LSC's edges and the attached photovoltaic cells. The size-dependent efficiency enhancement is studied for a single layer by changing the size up to 120 cm. The results show that the enhancement from the white diffuser drops and then tends to plateau at a certain size of LSC. This also applies to multilayer LSCs. Together with optical gel, the efficiency enhancement is higher for multilayer structures than that for single layers. We also demonstrate the optimal length for the design of LSCs due to reabsorption of dyes. These results could be applied to optimize the design of other LSCs.

Image-forming solar concentrators which project an image of the sun on the photovoltaic cell may have high thermodynamic efficiency, but suffer from non-uniform irradiance distribution and a nonsquare irradiance pattern. In this paper we discuss how to apply the Köhler illumination technique to solve these problems with an optimization approach. Two examples, a Fresnel lens-based concentrator and a two-mirror aplanatic system, are shown for demonstration. The uniformity of these systems is greatly improved by adding simple Köhler homogenizers in the form of aspheric lenses generated with our approach.

A model for the thermal properties of holographic planar concentrators on module performance is presented and verified with experimental data. The holographic planar concentrator modules consist of ribbons of volume holograms placed next to photovoltaic cells to achieve a low level concentration effect. The holographic ribbons increase the surface area required to produce a fixed amount of output power but reduce the cost of the module by eliminating approximately half of the photovoltaic cell material, in this case monocrystalline bifacial silicon cells. Due to the low concentration, the temperature reduction effect of the added surface area overcomes the added heat provided by the holograms. The theoretical point at which the added concentration by holograms overcomes the cooling effect provided by the extended region for varying theoretical holographic contributions is also presented.

A design methodology for low-concentration ratio holographic solar concentrators with one-axis tracking is investigated. This methodology maximizes the energy collected by cascaded holographic gratings and reduces diffracted beam cross talk between gratings. Several types of transmission gratings, optimized to work with single-axis tracking systems, are used in a cascaded configuration to concentrate a large fraction of the useable solar spectrum on the surface of photovoltaic cells. A model is developed that determines the energy yield of the holographic planar concentrator (HPC). Good agreement is found between simulation and measurement of a prototype system. Simulation of an optimized HPC design shows that 80% optical efficiency at 2X geometric concentration ratio is possible. The acceptance angle in the nontracking direction is ±65 deg, and a ±16-deg tracking tolerance is sufficient to maintain 80% of the maximum optical efficiency. Simulation also shows that the single-axis tracking HPC system has a 43.8% increase in energy yield compared to a nontracking holographic solar concentrator.

The properties of thin film InVO₄ photoanodes for water splitting have been studied. Compact films of InVO₄ were prepared by spray pyrolysis and are found to be stable between pH 3 and 11. Although the indirect bandgap is 3.2 eV, a modest amount of visible light absorption is observed. The origin of this absorption is attributed to the presence of deep donor states at ∼0.7 eV below the conduction band. These donor states presumably correspond to oxygen vacancies, which form as a result of small but unavoidable deviations of In:V from the ideal 1:1 stoichiometry during the wet-chemical synthesis process. Shallow donors are absent in this material, in contrast to what is normally observed for metal oxides. The deep donor model explains the much stronger visible light absorption of powders compared to thin films. The defect chemical reactions that lead to the formation of the deep donors are shown, and are supported by photoluminescence data.

We perform extensive density-functional theory total-energy calculations and ab initio molecular-dynamics simulations to evaluate the structure, stability, and reactivity of oxygen- and hydroxyl-decorated InP(001) surfaces for photoelectrochemical water cleavage. Surface oxygen is adsorbed in one of two primary local bond topologies: In-O-P and In-O-In. We show that the chemical activity of the oxygen-decorated surface toward water dissociation can be connected to the local oxygen bond topology, with In-O-In bridges promoting spontaneous water dissociation. Surface hydroxyl groups tend to form either In-OH-In bridges, though the second of the two In-OH bonds is easily broken. Dynamics simulations of the full water-semiconductor interface show surface proton transfer when the surface is hydroxylated, facilitated by strong hydrogen bonding between atop OH groups and with interfacial water molecules. Implications for understanding the reaction dynamics at InP(001)-water interfaces are discussed.

High-quality downconverted white light is important for many applications ,including general illumination. Downconversion of blue light from inorganic InGaN-based light emitting diodes to produce white light is demonstrated using red- and green-emitting phosphors. After characterization, films of the phosphors are prepared by mixing the powder into a polymethyl methacrylate host. The quality of light is improved and optimized by varying the weight ratio of green to red phosphors and the thickness of the phosphor layer.

This study investigates the optical performance of the MgF₂ layer coated on the SiN_x-based multicrystalline silicon (mc-Si) solar cell and optimizes the MgF₂ layer thickness. The experimental results are qualitatively consistent with the simulation results. The absolute efficiency of 6-inch mc-Si solar cells improve by 0.5 to 0.7% for different MgF₂ thicknesses and approach 17.2% absolute efficiency by measuring with an AM1.5G solar simulator. The optimized thickness of MgF₂ is 100 to 125 nm in ambient condition.

Weak absorption of light near the absorption band edge of a photovoltaic material is one limiting factor on the efficiency of photovoltaics. This is particularly true for silicon thin-film solar cells because of the short optical path lengths and limited options for texturing the front and back surfaces. Directing light laterally is one way to increase the optical path length and absorption. We investigate the use of a periodic array of apertures originated from bowtie aperture antennas to couple incident light into guided modes supported within a thin silicon film. We show the presence of the aperture array can increase the efficiency of a solar cell by as much as 39%.

The efficiency of thin film silicon modules needs to further improve in the long term to stay competitive with other photovoltaic technologies. Advanced super light trapping designs can be implemented in thin film silicon devices for this purpose. Different approaches are possible and in this work we report on plasmonic back reflectors and intermediate layers designed to enhance optical reflection over conventional device structures. Metal nanoparticles are embedded in thin film single and tandem junctions with the purpose to increase light scattering back into the active layers of the solar cell. Results show that metal nanoparticles do not compromise the electrical solar cell parameters; however, the current increase proves to be elusive in most cases. The data suggest that a better control of the metal nanoparticle size and distribution might be needed in order to harness the full benefits of plasmonic effects in thin film silicon devices.

Solar concentrator cells are typically designed for maximum efficiency under the AM1.5d standard spectrum. While this methodology does allow for a direct comparison of cells produced by various laboratories, it does not guarantee maximum daily, monthly, or yearly energy production, as the relative distribution of spectral energy changes throughout the day and year. It has been suggested that achieving this goal requires designing under a nonstandard spectrum. In this work, a GaInP/GaAs tandem solar cell is designed for maximum energy production by optimizing for a set of geographically-dependent solar spectra using detailed numerical models. The optimization procedure focuses on finding the best combination of GaInP bandgap and GaInP and GaAs sub-cell absorber layer thicknesses. It is shown that optimizing for the AM1.5d standard spectrum produces nearly maximum yearly energy. This result simplifies the design of a dual-junction device considerably, is independent of the optical concentration up to at least 500 suns, and holds for a wide range of geographic locations. The simulation results are compared to those obtained using a more traditional, ideal-diode model.

High-efficiency thin-film solar cells based on Cu(In,Ga)Se₂ are often formed by depositing precursor films and using a subsequent selenization step. We demonstrate a simple and cost-efficient approach simplifying both process steps by using a ternary Cu-In-Ga alloy target for sputter deposition of the precursor layer and by using a simple nonvacuum selenization reaction based on elemental selenium. In this contribution we examine in detail the characteristics of the precursor layers. The sputter growth is governed by a segregation of In-rich islands on top of a closed Cu-rich base. With optimized layers we could achieve conversion efficiencies well above 13% without the use of antireflective coating or metallic grids. The influence of the selenization duration on morphology and performance is discussed.

Cu₂ZnSnS₄ (CZTS) was obtained from a sol-gel precursor which consists of copper chloride, zinc chloride, tin chloride, and thiourea. CZTS thin films were prepared by spin-coating the sol-gel precursor followed by annealing in a nitrogen atmosphere. The morphology, composition, and structure of the absorber layer were studied by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and Raman scattering. The optical measurement shows the bandgap of these films is ∼1.51 eV, and the optical absorption coefficient is on the order of 10⁴ cm⁻¹. CZTS solar cells with a structure of low-alkali glass/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Al grid were tentatively fabricated. The best solar cell showed a short-circuit current density of 5.06 mA/cm2, an open-circuit voltage of 358 mV, a fill factor of 34.66%, and an efficiency of 0.63% under AM1.5 (100 mW/cm²) illumination. These results demonstrate the CZTS thin films were successfully deposited by a cheap sol-gel technique.

This PDF file contains the editorial “Editorial: Welcome to the Journal of Photonics for Energy” for JPE Vol. 1 Issue 1