[Show abstract][Hide abstract] ABSTRACT: In this work, we added Zonyl fluorosurfactant into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to improve the affinity of PEDOT:PSS and silicon nanowire (SiNW) arrays. The concentration of Zonyl fluorosurfactant is 0%, 0.1%, 0.5%, 1%, and 10%. The 0.5%-Zonyl treated PEDOT:PSS/SiNW solar cell has the highest open-circuit voltage of 0.541 V, but the best efficiency is the device with 0.1%-Zonyl treated PEDOT:PSS. The efficiency is 9.18%.
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Nov 2012 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Oct 2012 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: In this report, we demonstrate a new type of hybrid solar cell based on a heterojunction between the vertically aligned GaAs nanowires and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with incorporating poly(3-hexylthiophene) (P3HT) electron blocking layer. Under 1 sun simulated AM1.5 G solar illumination, the fabricated cell exhibits the power conversion efficiency of 9.2%. The fabrication of GaAs nanowire array adopts the top-down approach, which combines the low-cost monolayer nanosphere mask fabrication and the dry etching process with high quality single-crystalline GaAs wafer. The P3HT/GaAs heterojunction with a large conduction band offset will block the electron transportation from GaAs to PEDOT:PSS. Therefore, the electron transports toward the favorable Ti/Au electrode. Moreover, it is observed that the thickness of P3HT significantly influences the cell performance. Only the ultra-thin thickness is suitable for P3HT to act as an electron blocking layer without the negative influences on the cell performance.
No preview · Article · Oct 2012 · Solar Energy Materials and Solar Cells
[Show abstract][Hide abstract] ABSTRACT: We discovered that fringe structures of ZnO film in solar cells of inverted structures penetrate through the active layer made of low bandgap polymers. The ZnO penetration leads to leakage current of the solar cells. To prevent the ZnO penetration, the thin film morphology was modified. By changing the solvent and inserting TiO2 nanorods between ZnO film and the active layer, penetration can be avoided, so Rsh is improved from 110.3 Ω cm2 to 374.7 Ω cm2 and Voc from 0.36 V to 0.66 V. This result provides a promising route for employing low bandgap polymers to air-stable inverted structures with solution process. It is possible that inverted low bandgap polymer solar cells can achieve the goals of high performance and air stability.
No preview · Article · Jun 2012 · Solar Energy Materials and Solar Cells
[Show abstract][Hide abstract] ABSTRACT: Thin-film crystalline photovoltaic (PV) cell is a trend for future PV with its potential to achieve low cost and high efficiency. Concerning material utilization efficiency, we propose a method with a fast manufacturing method of thin crystalline Si by chemical solution. To obtain the highest efficiency of material utilization, experiments with different H2O2/HF ratio are conducted, where related mechanisms are discussed. Moreover, large-area (87.7 mm2) thin film transferred to glass is demonstrated, and with embedded nanohole structure, lowest optical reflectance of 0.26% is measured. These characteristics show that the fabricated thin film has potential for large-area crystalline thin film PV.
[Show abstract][Hide abstract] ABSTRACT: In this work, we develop a technique to form vertically aligned silicon nanowire (SiNW) arrays without aggregation at the top by cost and energy efficient metal-assisted chemical wet etching. The SiNW/PEDOT:PSS heterojunction solar cells are also fabricated with nanowire length varying from 0.758 °m to 5.27 °m. The 0.758-°m-SiNW/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cell has the best power conversion efficiency of 8.65% and short circuit current density of 24.94 mA/cm2.
[Show abstract][Hide abstract] ABSTRACT: In this work, we investigate in great detail the silicon nanowire (SiNW)/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid solar cells (SCs). Because of the light-trapping effect, SiNW/PEDOT:PSS SCs absorb more light than planar Si/PEDOT:PSS SCs. Also, the light absorption increases with the length of the SiNWs. However, the SiNW's length is not the only factor that influences the SCs. Thus the SiNW/PEDOT:PSS SCs with the shortest wire length of 0.37 μm have the best performance in terms of the highest power conversion efficiency of 8.40%, the largest short circuit current density of 24.24 mA cm−2, and open circuit voltage of 0.532 V, compared with the SCs of other wire lengths. The reasons are two-fold. First, long SiNWs tend to aggregate at the top portion, making the infiltration of PEDOT:PSS difficult, so the coverage of PEDOT:PSS on the SiNWs is not complete. Second, the increase of SiNW length greatly reduces the minority-carrier lifetime. Our investigation will help develop SiNW SCs with improved performance.
No preview · Article · Mar 2012 · Solar Energy Materials and Solar Cells
[Show abstract][Hide abstract] ABSTRACT: We report the performance enhancement of GaAs-based triple-junction solar cells using novel indium nanoparticles upon the cell front-surface to achieve the top cell current matching. The external quantum efficiency (EQE) enhancements of >; 5% in top cell at wavelengths from 350 nm to 450 nm are achieved as the cell with indium nanoparticles plasmonic structure. Besides increasing in short circuit current (ISC) of 11.20% (from 2.95 mA to 3.28 mA) and in conversion efficiency (η) of 13.5%(from 20.8% to 23.6%) are also obtained under one sun AM1.5G illumination.
[Show abstract][Hide abstract] ABSTRACT: We report the increasing in average external quantum-efficiency (EQE) of 11% on the top-cell of GaAs-based triple-junction solar-cell due to current matching using a graded-index SiO2-nano-pillars sub-wavelength/SiO2/TiO2 AR-coating by CF4-RIE etching with Ag-nanoparticles mask.
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Sep 2011 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: 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 5Ã¬m-20Ã¬m 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.
No preview · Article · Sep 2011 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Ultra short silicon nanowires (SiNWs) were applied on Si/Poly(3,4-ethylenedioxy-thiophene): poly(styrenesulfonate) (PEDOT:PSS) solar cells by solution process. The short circuit current density (Jsc) is 23.72 mA/cm2, and power conversion efficiency (PCE) is 7.38%.
[Show abstract][Hide abstract] ABSTRACT: Si nanostructures are promising materials for future photovoltaic applications. To date the Si nanostructures are mainly formed on particular substrates or at high temperatures, greatly limiting their application flexibility. Here we report a two-step metal-assisted etching technique for forming vertically aligned Si nanohole thin films on bulk Si wafers at room temperature. The Si nanohole thin films with a thickness of 5µm can be easily transferred to alien substrates. Because of the low temperature transfer process, it enables a large variety of alien substrates such as glass and plastics to be used. In addition, we demonstrate that the bulk Si substrate can be reused to fabricate Si nanohole thin films. The consumption of bulk Si materials is significantly reduced.
[Show abstract][Hide abstract] ABSTRACT: In this research, we compare hydrothermally synthesized TiO2 nanorods in an unsealed and a sealed system, respectively. Due to the variation of hydrothermal concentration, the morphology is very different. Then we further pre-fabricate a TiO2 seed layer by the sol-gel method and then hydrothermally synthesize TiO2 nanorods. The TiO2 nanorods can also be grown on the TiO2 seed layer successfully. This result exhibits the promising potential for the growth of TiO2 nanorods on versatile substrates.
[Show abstract][Hide abstract] ABSTRACT: A technique applying the homogenized KrF excimer laser reformation to fabricate Si cylindrical profile is presented. High-power excimer laser was used to illuminate high-aspect-ratio Si ridges which were fabricated using typical lithography and etching process. The Si ridges were then melted and reshaped to cylinders due to surface tension. The structure can be further preceded by thermal oxidation to produce wave guiding photonics. It is capable of fabricating sub-micrometer Si waveguides with extremely smooth surface.
[Show abstract][Hide abstract] ABSTRACT: Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells were fabricated by solution process. The effect of nanowire length to cell performance was investigated for the nanowire length varying from 0.73 μm to 5.59 μm. The nanowire length was found to have negative effect on the power conversion efficiency (PCE), in the condition of the fixed thickness of PEDOTPSS. The highest PCE of 7.02% was obtained for the wire length of 0.73 μm.
No preview · Article · Jun 2011 · Conference Record of the IEEE Photovoltaic Specialists Conference
[Show abstract][Hide abstract] ABSTRACT: 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 Omega-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/cm(2) 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.
No preview · Article · Apr 2011 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Various Si nanostructures can be fabricated using a metal-assisted etching technique, which must be applied on bulk Si wafers,
limiting its applications and wasting a significant amount of material. Here, we report a technique to form a Si nanostructured
thin film created by metal-assisted chemical etching from bulk Si wafers and to transfer it onto alien substrates. To detach
the Si nanostructured thin films completely from bulk Si wafers, a second-step metal-assisted chemical etching made the root
of the Si nanostructures become fragile. The transferred Si nanostructures are well-aligned along the normal direction of
the receiver substrate. The X-ray diffraction spectrum reveals that the transferred Si nanostructured thin films exhibit good
crystal orientation and morphology. A strong light trapping effect between the nanostructures causes such films of
thickness to exhibit nearly 99% absorption from
. This exceeds the theoretically calculated limits of planar Si.
[Show abstract][Hide abstract] ABSTRACT: We report the influence of controlled lengths and densities of GaN rod arrays on the output power of GaN light-emitting diodes (LEDs). The morphology-controlled GaN rod arrays are fabricated via using ZnO rod arrays as a dry etching mask. Our investigation indicates that the output power of GaN LEDs has a strong dependence on the lengths and densities of GaN rod arrays. The variation of output power of GaN LEDs with GaN rod arrays is caused by the Fabry-Pérot resonance of the film composed by GaN rod arrays. The theoretical analysis also shows a good agreement with the measurement results.
No preview · Article · Jan 2011 · IEEE Photonics Technology Letters