Fabrication And Photovoltaic Applications Of Silicon Nanowires Array

Photovoltaic technology is one of the effective ways to solve the energy crisis and environmental pollution. At present, crystalline silicon solar cells remain the basis of the current photovoltaic industry. However, the high cost of crystalline silicon solar cells has greatly hindered the development of the photovoltaic industry. Silicon nanowires(SiNWs) are considered as promising materials to achieve high efficiency, low cost solar cells, due to their excellent light absorbing properties and efficient carrier separation performance. Therefore, the research on silicon nanowire arrays for photovoltaic applications is very meaningful. In this paper, the antireflection properties of SiNWs array, solar cell performance, as well as surface passivation of SiNWs array has been researched. The results we obtained are as follows:(1) The SiNWs array can be created by metal-assisted chemical etching (MACE) as the Ag nanoparticles film vertically sink. The length of SiNWs arrays can be regulated by adjusting the etching time. The lengths of SiNWs array increase linearly with etching time for silicon substrates. Silicon nanowire arrays has a low reflectance (<1%) over a wide range (300-1000nm).The SiNW arrays of longer length have lower reflectance in our investigated length range. The SiNW solar cell exhibits a higher power conversion efficiency of8.84%than the cell based on polished silicon wafer, under the same condition of compact contact of the front surface electrode. We found that the reason for the increase of cell efficiency, in addition to the excellent antireflection properties of SiNWs arrays, is the improved long-wavelength sunlight absorption which reduces the recombination of minority carrier.(2) The length of the SiNWs arrays can be manipulated by adjusting the reaction time. The reflectance decreases with the SiNWs’length increasing. By combining thermal oxidation and hydrofluoric acid treatment, we can manipulate the filling ratio of SiNWs. With the SiNWs’filling ratio decreasing, the reflectance decreases at first, and then increases. Si/SiO2coaxial nanowires array can be obtained by thermal oxidation of as-grown SiNWs array. The results show that the silicon dioxide shell can not only further reduce the reflectance of SiNWs array, but also passivate surface states of SiNWs array. Finally, by combining the manipulation of wire length, filling ratio and coaxial structure, we obtain the SiNWs array with the optimized structure which shows a minimum reflectance less than0.9%in the 400-1000nm wavelength range.(3) The silicon nitride thin film deposited by PECVD form coaxial nanowires structure with SiNWs. Annealing under4000C can enhance the lifetime of the as-deposited SiNWs array sample, because Si-H bonds in the silicon nitride thin film are broken and diffuse to the interface between film and SiNWs to passivate the dangling bonds of SiNWs. In addition, the information of deep energy level of the interface of silicon nitride film and SiNWs arrays indicates, both the density and carrier recombination capacity of traps, the sample after heat treatment is better than the as-deposited sample. This result also confirms the effect of passivation of silicon nitride film for SiNWs array. The performance of SiNWs solar cell is significantly improved after the silicon nitride thin film deposition, and its power conversion efficiency is enhanced from12.83%to14.47%.