Improvement in a-Si:H silicon solar cells with using double p-type window layers based on nanocrystalline silicon oxide

Abstract

In this study, our objective was to analyze by simulation the effect of using two different double p-type layers, one p-type based on hydrogenated nanocrystalline silicon (nc-Si:H) and the other p-type based on hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) on the performances of n-i-p a-Si:H based solar cell. The AMPS-1D computer code is used to realize the simulation. Two devices were simulated and compared, the first structure device is:metal/n-a-Si:H/i-a-Si:H/p-nc-SiOx:H/p+nc-SiOx:H/ITO and the second structure device is:metal/n-a-Si:H/i-a-Si:H/p-nc-Si:H/p+nc-Si:H/ITO. An improvements in the JSC in the case of structure with p nc-SiOx:H layers is mainly due to the good absorption in the short wavelength range which is causes by the presence of oxygen in the high band gap p-nc-SiOx:H layer and which makes it more transparent. This good light absorption leads to a high photocarriers generation which combined with a high doping concentration to extract holes from the active layer. The presence of the p-nc-SiOx:H buffer layer at the i/p-window interface reduces the recombination at this interface and improves the VOC. For the optimized window layer parameters values: NDG = NAG = 1017 cm−3, L = 15 nm, NA = 5 × 1019 cm−3 and with NA = 1018 cm−3 for the buffer layer, the best performances were obtained in the case of solar cell with double p-nc-SiOx:H type window layers (JSC = 13.80 mA/cm2, VOC = 934 mV, FF = 79.1% and Eff = 10.21%).