Performance enhancement of thin-film silicon solar cells by development of core component layers

Abstract

High efficiency thin-film silicon (Si) solar cells were prepared on flexible substrates by the plasma-enhanced chemical vapor deposition method. To improve their performance, the microstructural, electrical, and optical properties of the core component layers including the metal rear reflectors, p- and n-type doped layers, and intrinsic absorber layers were controlled sophistically. To enable the use of flexible substrates with low heat resistance as well as to enhance light-scattering properties, nanotextured rear reflectors with a Ag/Al:Si bilayer structure were developed by dc magnetron sputtering at a low substrate temperature of below 150 °C. Highly crystalline n-doped seed layers (which effectively eliminate a defect-dense amorphous region formed in the initial growth stage of intrinsic nanocrystalline silicon (nc-Si:H) absorber layers) and p-type wide-bandgap nanocrystalline silicon carbide (nc-SiC:H) window layers (which reduce the parasitic absorption loss in the short-wavelength region and increase the open circuit voltage (VOC)) were successfully applied to enhance the performance characteristics of the solar cells. Through the combination of the developed core component layers, high conversion efficiencies of 8.84% (VOC = 0.53 V, JSC = 25.28 mA/cm2, and fill factor (FF) = 0.66, where JSC is the short circuit current) and 7.48% (VOC = 0.50 V, JSC = 21.07 mA/cm2, and FF = 0.71) were obtained for nc-Si:H solar cells fabricated on stainless steel (SUS) and polyimide substrates, respectively, at a low substrate temperature of below 150 °C. Flexible a-Si:H/nc-Si:H double-junction solar cells fabricated on SUS substrates showed a high conversion efficiency of 11.46% (VOC = 1.38 V, JSC = 11.53 mA/cm2, and FF = 0.72) when the nc-Si:H solar cells developed in this study were applied as a bottom cell.