Dember effects in a-Si:H solar cells

The origin of the open circuit voltage (Voc) difference between N-I-P and P-I-N a-Si solar cells is discussed herein. Vocof N-I-P a-Si:H solar cells is larger than that of P-I-N a-Si:H cells by more than 100 mV, while other photovoltaic data such as FF and Jscare almost identical. Since the undoped (I)-layer is the active region and thermal equilbrium carrier concentration in the active region is very low (less than 10¹⁰cm^-3), the large difference in electron and hole mobility values ( ) causes a Dember field. This Dember field in the undoped region is always positive (directed away from the junction) in both N-I-P and P-I-N cells. The Dember field aids carrier collection in N-I-P cells but opposes carrier collection in P-I-N cells. Photogenerated current at high forward bias may be influenced by this Dember field which can explain the Vocdifference in N-I-P and P-I-N cells.