Achieving high power conversion efficiency (PCE) without compromising device stability is an essential trade-off for commercializing organic solar cells (OSCs). In this study, a novel organic-inorganic hybrid material of tin oxide (SnO2) nanoparticles (NPs) and perylene diimide derivative (PDINO) is introduced as the electron transport layer (ETL) to improve both the device performance and the device stability of non-fullerene OSCs. Compared with the pristine SnO2 NP ETL-based device, not only the PCE of the PM6:IT-4F OSC with SnO2:PDINO as ETL is efficiently improved from 11.3 % to 12.7 %, but the shelf life of the SnO2:PDINO ETL based device is also extended. After being stored in ambient condition without encapsulation for 360 h, the PCE of the modified ETL-based OSC still retains 80 % of its original value. The incorporation of PDINO dopant can provide more favorable interfacial properties between the ETL and the active layer as well as reduced surface defects of SnO2 NP ETL, thus contributing to charge transport efficiency, suppressing molecular recombination, and protecting the active layer from degradation.
KEYWORDS: Perovskite, Crystals, Scanning electron microscopy, Solar cells, Molecules, External quantum efficiency, Absorption, Solar energy, Crystallography, Electron transport
Perovskite has attracted enormous research interest due to the unique advantages, such as high absorption coefficient, great carrier mobility, low exciton binding energy, etc., providing desirable applications in high-performance perovskite solar cells (PSCs). However, the current density-voltage (J-V) hysteresis phenomenon in PSC will reduce the testing accuracy and weaken the actual device performance. In this paper, a facile method based on interfacial engineering is proposed to suppress the hysteresis phenomenon and the deeper physicochemical mechanism is systematically analyzed. By incorporating non-fullerene acceptor Y6 in the crystallization process, a denser and continuous perovskite film with a low-density defect state is obtained, which affords PSC dramatically suppressed the J-V hysteresis with the hysteresis difference decreasing from 13.6% to 1.9% at the maximum power point. Furthermore, scanning electron microscope results and energy dispersive spectrum mappings suggest that ultrathin Y6 film is deposited between the perovskite film and the hydrophobic electron transport layer of PC61BM. The improvement of wettability and matching energy level caused by Y6, render the photocurrent increase and the power conversion efficiency of PSC@Y6 high up to 17.5%. Thus, this work demonstrates that interfacial engineering using small-molecule non-fullerene acceptor is a promising strategy to suppress the J-V hysteresis limiting further PSC commercialization.
KEYWORDS: Solar cells, Solar energy, Polymers, Organic photovoltaics, Doping, Molecules, Resonance energy transfer, Photovoltaics, Absorption, Molecular energy transfer
In this work, we fabricated the ternary bulk hetero junction (BHJ) polymer solar cells (PSCs) by doping a phosphorescent small molecule bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium(acetylacetonate)[(tbt)2Ir(acac)] into the conventional active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). After doping (tbt)2Ir(acac), the short circuit current and fill factor are simultaneously enhanced compared with binary device and the power conversion efficiency (PCE) of P3HT:PC71BM based ternary devices is improved from 2.99% to 4.14%. More excellent photovoltaic performance of ternary PSCs is mainly attributed to enhanced charge transportation by appropriate energy cascade alignment and enhanced exciton harvesting by Foerster resonance energy transfer from (tbt)2Ir(acac) to P3HT.
Perovskite solar cells (PVSCs) based on the hybrid organic/inorganic structure have shown great prospect to the development of low cost, flexible, lightweight, and simple processability. But there are still exist many problems that limit its further commercial applications, such as the low mobility of hole transporting layer (HTL) and the poor stability which caused by the external environment and internal degradation. In this work, we demonstrated that the mixed HTL with poly-TPD and PTAA can increase the performance of p-i-n PVSCs. By doping poly-TPD into PTAA, the devices with mixed HTL show significantly enhancement of short-circuit current and fill factor, with an optimized power conversion efficiency (PCE) obtained over 20% enhancement compared with the control devices with bare PTAA, and the best PCE reaches 14.6%. Detailed analysis shows that the performance enhancement can be explained to the improved perovskite grain size and the increased electron transfer of mixed HTL. As a result, by incorporating poly-TPD with PTAA as the HTL, it provides an effective approach to reach high performance p-i-n PVSCs.
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