Impacts of an intrinsic a-Si buffer layer between the p-type nc-Si layer and the intrinsic a-SiGe layer in single junction solar cells

This paper reports numerical modeling and experimental investigation for the impacts of an intrinsic a-Si buffer layer between the p-type nc-Si layer and the intrinsic a-SiGe layer with a narrow bandgap of 1.40-1.55eV on the performances of a-SiGe single junction solar cells. The effects of bandgap and thickness of the buffer layer were simulated by using Analysis of Microelectronic and Photonic Structures (AMPS) computer model developed at Penn State University. The results obtained by the simulation show that the intrinsic a-Si buffer layer can lead to an increase in the open circuit voltage (V_oc), but cause a decrease of the fill factor (FF) and the conversion efficiency (Eff), depending on how large the band gap and thickness of the buffer layer are. Our experimental results are consistent with the simulation´s results; i.e., a thick and wide-bandgap buffer layer between i and p layers can cause a serious deterioration in FF. An optimal a-SiGe single junction solar cell without the a-Si buffer layer has achieved an efficiency of 9.41% with V_oc=0.576V, J_sc=23.34 mA/cm², and FF=70.0%.