Chen

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.

Electrode-contact enhancement in silicon nanowire-array-textured solar cells

In the case of the silicon (Si) nanowire (NW)-array-textured solar cells, the electrode-contact enhancement has been achieved using a simple and convenient double-step diffusion process to form a highly doped N+ region at the tips of a Si-NW array. The series resistance can be effectively reduced, leading to an increase in the short-circuit current density in the cell. We have studied the physical mechanism of the impact of an increase in doping level at the tips of a Si-NW array on the electrode-contact property, which would benefit in realizing an improvement in cell performance in such a nanostructure solar cell.

Effects of buffer layer and substrate temperature on the surface morphology, the domain structure and magnetic properties of c-axis-oriented Nd2Fe14B films

Anisotropic Nd-Fe-B thin films with c-axis texture are fabricated by dc magnetron sputtering on heated Si substrate. The influence of Ti or Mo buffer layer thickness and substrate temperature on the surface morphology, the domain structure and the magnetic properties are investigated and compared for the Nd-Fe-B films. It is found that the morphology of the surface strongly depends on the thickness of the buffer layer. A rough surface is observed if there is no buffer layer between the substrate and Nd-Fe-B layer or the buffer layer is too thick. Mo shows to be the better candidate for the buffer layer for its perfect lattice match with the Nd-Fe-B layer. The best values for the maximum energy products are 11.9 and 14.8 MGOe for the Nd-Fe-B films with Ti and Mo buffer layers, respectively. (c) 2005 American Institute of Physics.

Surface passivation of nano-textured silicon solar cells by atomic layer deposited Al2O3 films

In the work, the surface recombination of silicon nanostructures was investigated. Silicon nanostructures were synthesized using technique of silver catalyzed chemical wet etching, and the passivation layers of SiNx and Al2O3 were deposited on the samples. The thermal atomic layer deposited Al2O3 can conformally cover the rough surface and reduce the defect density of the nanostructures. Moreover, the negative fixed charge in Al2O3 layer introduces the surface field effect passivation. The lifetime measurement result indicates that Al2O3 layers offer much better passivation effect on the silicon nanostructure surface than SiNx layers. The silicon nano-textured solar cells with SiNx and Al2O3 passivation layers were manufactured and measured. The results show that the enhanced solar cell performance was achieved by Al2O3 passivation.

Effect of heat treatment on microstructure and magnetic properties of anisotropic Nd-Fe-B films with Mo or Ti buffer layer

High coercivity Nd–Fe–B films with c-axis texture perpendicular to the film plane have been prepared by dc magnetron sputtering and subsequent heat treatment. The influences of heat treatment and buffer layer materials (Mo and Ti) on the microstructure and magnetic properties of the Nd–Fe–B films are investigated. For the film with Mo buffer layer, when the substrate temperatures (Ts) are below the crystallization temperature (Tcr), the as-deposited films are identified to be soft magnetic with a mazelike stripe magnetic domain structure. After subsequent heat treatment, Nd2Fe14B phase forms with c-axis texture perpendicular to the film plane, and the domain structure is not mazelike anymore. The coercivity of the annealed films increases with decreasing Ts and the highest coercivity of about 22.8 kOe has been achieved. For the film with Ti buffer layer, the heat treatment also results in changing the magnetic domain structures from a mazelike pattern to a disordered pattern. Atomic force microscopic obse...

Silicon nanostructure solar cells with excellent photon harvesting

Silicon (Si) nanostructure solar cells have been synthesized using a nanowire (NW) array as the surface texturing. Optical-reflection measurement exhibits an excellent photon-harvesting property for the Si-NW-array texturization. Less than 2% reflection ratio at an 800 nm wavelength was achieved. Results show that an optimized 125×125 mm2 Si nanostructure solar cell with an excellent photon-harvesting property has a 35.4% higher energy-conversion efficiency than the c-Si solar cell due to its enhanced optical-absorption characteristics. However, for the nanostructured solar cells, the decrease in external quantum efficiencies in the short-wavelength region proves that the surface recombination plays a critical role in determining the final quantum-efficiency performance, indicating that optimum surface passivation was a prerequisite in high-efficiency Si nanostructure solar cells.

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...