Wuchang Ding

Influence of nanowires length on performance of crystalline silicon solar cell

Silicon-nanowire (Si-NW) array, prepared by an electroless chemical-etching method, shows excellent optical antireflection property over a wide spectral bandwidth. The influence of the wire length on the optical antireflection property and the solar cell performance were studied for both the Si-NW array solar cells and the planar solar cells. The reflectance of NWs solar cells is almost invariable and much lower than that of the planar solar cells but the performance of planar solar cells is the best. Results show the performance of NWs solar cells is strongly affected by some other factors such as surface passivation and electrode-contact property.

Silicon nanowire-array-textured solar cells for photovoltaic application

In this paper, a vertical-aligned silicon nanowires (Si NWs) array has been synthesized and implemented to the Si NW-array-textured solar cells for photovoltaic application. The optical properties of a Si NWs array on both the plane and pyramid-array-textured substrates were examined in terms of optical reflection property. Less than 2% reflection ratio at 800 nm wavelength was achieved. Using leftover monocrystalline Si (c-Si) wafer (125×125 mm2), a 16.5% energy conversion efficiency, with 35.4% enhancement compared to the pyramid-array-textured c-Si solar cells, was made by the Si NW-array-textured solar cells due to their enhanced optical absorption characteristics. However, without SiNx passivation, the short circuit current reduced due to the increased surface recombination when using Si NWs array as surface texturing, indicating that an optimum surface passivation was prerequisite in high-efficiency Si NW-array-textured solar cells.

Room temperature photoluminescence of tensile-strained Ge/Si0.13Ge0.87 quantum wells grown on silicon-based germanium virtual substrate

National Basic Research Program of China [2007CB613404]; National Natural Science Foundation of China [60676027, 50672079]; Key Projects of Fujian Science and Technology [2006H0036]; Program for New Century Excellent Talents in University

Antireflection properties and solar cell application of silicon nanostructures

Silicon nanowire (Si NW) arrays were fabricated on polished and pyramids textured mono-crystalline Si (mc-Si) using an aqueous chemical etching method. The Si NWs and a hybrid texture of NWs and pyramids both show strong anti-reflectance properties in the wavelength region of 300–1000 nm, with the minimum average reflectance of 2.52% and 8%, respectively. The above two nanostructures were fabricated on mc-Si solar cells with the area of 125×125 mm2. Then the influences of Si NWs and hybrid textures on the performances of mc-Si solar cells created using different fabrication processes were analyzed by internal quantum efficiency measurement and by systematical comparisons of efficiency, filling factor, open circuit voltage and short-circuit current. Passivation is found to be essential for the hybrid textured solar cells, and the average open circuit voltage can be improved by 7% after a passivation layer was deposited. The short circuit current could be increased when Si NWs were fabricated on a substrate...

Design of two dimensional silicon nanowire arrays for antireflection and light trapping in silicon solar cells

Silicon nitride coated nanowire arrays have been investigated as an efficient antireflection structure for silicon solar cells. The minimum average reflectance could reach 1.62% under AM1.5 spectrum. Scattering effects of silicon nanowire arrays also result in enhanced absorption in the substrate, and analytical results show that the scattered light can be well trapped in silicon substrate when the back surface is passivated by silicon dioxide. This ultra-low surface reflection property combined with light trapping effect may have potential applications in silicon solar cells with thin substrate.

Numerical simulation and modeling of spectral conversion by silicon nanocrystals with multiple exciton generation

Silicon nanocrystals (Si-NCs) were applied on the front surface of a conventional silicon solar cell. Considering absorption with multiple exciton generation (MEG) yields and consequently photoluminescence, the cell performance was simulated based on a numerical model founded on experimental results in literature. The results show that the cell efficiency could be prominently enhanced by MEG yields and spectral down-conversion. However, though MEG yields could reach 250% within Si-NCs, it only contributes 8.7% to the cell efficiency enhancement while wavelength shifting dominates the cell efficiency enhancement mechanism. Additionally, extraction factor which is defined as ratio of photons extracted from Si-NCs to the generated carries in Si-NCs is the most critical parameter for cell performance improvement. Therefore, to realize this novel structure cell, further experimental work should be lay on improving MEG efficiency as well as photoluminescence efficiency and optical confinement of the photolumine...

Maskless fabrication of selectively sized silicon nanostructures for solar cell application

A two-step maskless method was used to synthesize silicon nanostructures. In the first step, silver nanoparticles were formed through rapid thermal annealing of silver thin films. The temperature, duration of annealing, and initial thickness of the silver film jointly determined the distribution and diameter of silver particles. In the next step, silicon nanostructures were created using silver catalyzed etching in HF/H2O2. The experiment confirmed that the final sizes of the nanostructures corresponded to the diameters of the silver particles. Further, silicon nanostructure-textured solar cells were manufactured and tested. The surface-reflection ratio of the cells can be decreased to 5% in the 300–1000 nm wavelength range. The current-voltage and quantum efficiency measurements also reveal that silicon nanostructure-textured solar cells exhibit considerable light trapping enhancement. The results also indicate that effective passivation and electrode contact are important for those cells.

Light confinement for silicon solar cells with thin substrate

Thinner silicon substrate are expected to be used in silicon solar cells for cost reduction. In this contribution, we numerically discussed a series antireflection structure for light confinement design that may be applied to silicon solar cells with thin substrates. The results show that nano-pillar-array with silicon nitride coating has a very low reflectance over the whole response region of silicon solar cells. The average reflectance could reach 2.34%, which is fundamentally coincident with reported experimental results. Planar reflection at the back surface of the cell was investigated for light confinement application. Enhanced light absorption of the cell has achieved with high reflectance of the back surface, while the front surface reflectance also increased prominently. Based on the simulation results, back surface scattering with high reflectance were proposed for better light confinement in silicon solar cells with thin substrates.

Formation of silicon nanocrystals embedded in high-κ dielectric HfO2 and their application for charge storage

Annealing thin films of silicon containing HfO2 films deposited by an electron-beam coevaporation produces silicon nanocrystals embedded in high-κ dielectric HfO2. Such films can be used to fabricate nonvolatile memory devices. By changing the Si content in the precursor HfSixO2 (x=1, 2, 3, or 4) film, the size and density of silicon nanocrystal could be controlled and high-density of silicon nanocrystals could be obtained. Transmission electron microscopy observations showed that the maximum density of silicon nanocrystals was as high as 1.3×1013 cm−2 for HfSi4O2 and the average nanocrystal diameter was 4.3 nm. The metal-oxide semiconductor capacitor memory structure with embedded silicon nanocrystals in HfSi4O2 exhibited the largest memory window, 3.94 V under ±5 V sweep voltage.