In the past decades, Si has been the most important material for electronics. By exploiting this mature semiconductor
fabrication technique, it is also highly desired to use Si for applications in other areas. Here we report the use of Si
micro-structures for optical-communications and Si nano-structures for energy applications. Sub-micron Si waveguides
is fabricated on Si substrates rather than SOI (silicon on insulator) substrate using laser reformation technique. This
method helps solve the incompatible problem for the integration of optics and electronics on a single Si chip. The typical
thickness of the oxide layer on the CMOS transistor layer is below 100nm which, however, creates excessive optical loss
due to the light coupling into Si substrate. Besides, fabricating Si photonics on Si wafer is much cheaper than that on SOI
wafer. The method is using high-power pulse laser to melt high-aspect ratio Si ridges. This creates a structure with wider
upper portion and narrower lower portion, which can be further oxidized and forming waveguides. For energy
applications, Si nanostructures are fabricated using the metal-assisted chemical etching (MacEtch) technique. Si
nanostructures could greatly reduce the surface reflection to enhance light harvest. In addition, Si nanowires are further
combined with organic materials to form hetero-junction solar cells using low-cost solution process. Furthermore, the Si
nanostructures and MacEtch process are refined to form completely single-crystal Si thin film. Thus the material cost of
Si solar cells can be potentially reduced to only 1/10 of current ones.
Silicon nanowire (SiNW) arrays are widespread applied on hybrid photovoltaic devices because SiNW arrays can substitute the pyramid texture and anti-reflection coating due to its strong light trapping. Also, SiNWs can be prepared through a cost-efficient process of metal-assisted chemical etching. However, though longer SiNW arrays have lower reflectance, the top of long SiNWs aggregate together to make junction synthesis difficult for SiNW/organic hybrid solar cell. To control and analyze the effect of SiNW array morphology on hybrid solar cells, here we change the metal deposition condition for metal-assisted chemical etching to obtain different SiNW array morphologies. The experiment was separated to two groups, by depositing metal, say, Ag, before etching (BE) or during etching (DE). For group BE, Ag was deposited on n-type Si (n-Si) wafers by thermal evaporation; then etched by H2O2 and HF. For group DE, n-Si was etched by Ag+ and HF directly. Ag was deposited on n-Si during etching process. Afterwards, residual Ag and SiO2 were removed by HNO3 and buffered HF, successively; then Ti and Ag were evaporated on the bottom of Si to be a cathode. Finally, SiNWs were stuck on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) that was spincoated on the ITO coated glass to form SiNW/organic heterojunction. The results show that group BE has reflectance lower than that in group DE in solar spectrum. However, group BE has smaller power conversion efficiency (PCE) of 8.65% and short-circuit current density (Jsc) of 24.94 mA/cm2 than group DE of PCE of 9.47% and Jsc of 26.81 mA/cm2.
Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer.
Reducing the large amount of Si material consumption is thus a critical issue. Here we develop a two-step metal-assisted
etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si
nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO3/ HF aqueous
solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the
nanohole structure at the second-step metal-assisted etching. All the processes can proceed at around room temperature.
A Si nanohole thin film with an average hole-size of 100 nm and a thickness of 5ìm-20ìm was hence formed at the top
of the wafer. Afterwards, the Si nanohole thin film was transferred onto alien substrates. The Si nanohole thin film has
the crystal quality similar to the bulk Si wafer. The above bulk Si substrate can be reused. With similar processes, other
Si nanohole thin films can be formed from the above recycled Si wafer. The hole size and thickness are similar. The Si
wafers recycled will significantly reduce the material consumption of Si. Thus, such technique is promising for lowering
the cost of Si solar cells.m.
Conventional manufacturing processes of solar cells, including epitaxy, diffusion, deposition and dry etching, are
high cost and high power consumption. To save energy and reduce expenses, we use organic material, silicon
nanostructure and solution process. The devices structure is n-type bulk Si (n-Si)/n-type silicon nanowires (n-
SiNWs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) heterostructure. The active region
includes n-Si and n-SiNW arrays, promising the property of ultra low reflection for high light absorption. In this work,
SiNWs of only a-few hundred nanometers could lower the reflectance to below 5%. In addition, an organic material -
PEDOT:PSS, instead of p-type doping, is introduced to form a p-n junction with n-Si/n-SiNWs for separating the
electron-hole pairs. The use of PEDOT:PSS can also passivate the surface defects of n-SiNWs.
N-type SiNW arrays are made by aqueous etching process. The etchant contains Ag+ and HF etching vertically to
the 1-10 Ω-cm Si (100) wafers. After etching and removing residual Ag and SiO2 by nitric acid and diluted HF
successively, n-SiNW arrays existed on either surfaces of n-Si with very dark color; then Ti and Ag were evaporated on
n-Si to be a cathode. Finally, nanowires of n-Si/n-SiNWs were stuck on the PEDOT:PSS that were spin-coated on the
ITO coated glass to form a core-sheath heterojunction.
The performance and quantum efficiencies (QE) were measured. The short circuit current density and power
conversion efficiency are 27.46 mA/cm2 and 8.05%, respectively, which are higher than other solar cells containing
SiNWs. The external and internal QE are beyond 50% and 60% in visible range, respectively.
We have demonstrated a new type of hybrid solar cell based on a heterojunction between poly(3,4-
ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and vertically aligned n-type GaAs nanowire (NW)
arrays. The GaAs NW arrays are directly fabricated by the nano-etching of GaAs wafer with spun-on SiO2 nanospheres
as the etching mask through inductively coupled plasma reactive ion etching (ICP-RIE) system. Then we attach GaAs
NW arrays onto PEDOT:PSS conductive polymer to form a p-n junction. According to our research, the morphology of
GaAs NW arrays strongly influences the characteristics of the GaAs NW/PEDOT:PSS hybrid solar cells. The improved
interpenetrating heterojunction interface and the suppressed reflectance of GaAs NW arrays will offer great
improvements in efficiency relative to a conventional planar cell. The power conversion efficiency of 5.8 % of GaAs
NW/PEDOT:PSS cells under AM 1.5 global one sun illumination can be achieved.
The characteristics of the well-aligned silicon nanowire/poly(3,4-ethylenedioxy- thiophene):poly(styrenesulfonate)
(PEDOT:PSS) heterojunction solar cells are investigated. The PEDOT:PSS adheres on the n-type silicon nanowire
surface to form core-sheath heterojunction structure. A novel front contact is proposed here to enhance the carrier
collection efficiency for the nanostructured emitter. The cells exhibit stable rectifying diode behavior. Such structure
increases the area of junctions and shortens exciton diffusion distance, and therefore greatly increases exciton
dissociating probability. Compared to the devices without nanowire structure, the power conversion efficiency improves
from 0.08 % to 4.99 %.
Poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonic acid) (PEDOT:PSS) is a common material of hole
injection layer used in polymer light emitting diodes (PLEDs) and organic solar cells. It can improve the efficiency of the
charge collection at the anode. It has been reported that adding glycerol to PEDOT:PSS could increase the conductivity
and improve the efficiency of PLEDs and organic solar cells. However, it is less noticed that the conductivity could be
improved when the solution of PEDOT was heated before deposition. Here we experimented different concentrations of
glycerol into PEDOT:PSS to make G-PEDOT:PSS solution, and heated the G-PEDOT:PSS solution at different
temperatures before deposition. The solutions are then spin-coated on the glass and annealed at 140 °C. The conductivity
was then measured and compared. The experiments showed that the conductivity of pure PEDOT:PSS slightly increased
for 2-3 times, while the G-PEDOT:PSS increased over two orders of magnitudes. The conductivity increased with the
heating temperature before deposition. The enhancement of the conductivity of the G-PEDOT:PSS film was higher than
that of the pure PEDOT:PSS film. The overall conductivity increase for over three orders of magnitude. The reason is
because the high temperature causes the glycerol and PEDOT:PSS to mix evenly. This is helpful for the swelling and
aggregation of colloidal PEDOT-rich particles, forming a highly conductive network. When G-PEDOT:PSS resistance is
reduced, it may not only increase the hole collection ability, but also replace ITO as the anode layer due to its advantages
of low production cost and high work function.
We demonstrate the method of transferring aligned single crystal silicon nanowires (SiNWs) to transparent
substrate. The alignment of the transferred nanowires is almost identical to the original one. The density of the
transferred SiNWs can achieve 3×107 nanowires/mm2. The low temperature fabrication processes are compatible for a wide range of substrates. The transmission coefficient below 10 % at a wide bandwidth, 400-1100 nm, was found in the transferred SiNWs. The high dense aligned SiNWs are promising for future photovoltaic applications.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.