Two-Dimensional Simulations of Interdigitated Back Contact Silicon Heterojunctions Solar Cells

Abstract

Interdigitated back contact silicon heterojunction (IBC-SiHJ) solar cells that combine the amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction- and interdigitated back contact (IBC) concepts are very promising in order to reach the highest one-junction efficiencies. In this chapter, a comparative two-dimensional simulation study has been done on the IBC-SiHJ structure based on n-type and p-type crystalline silicon by varying the values of the following parameters: minority carrier lifetime in c-Si, c-Si thickness, c-Si doping concentration, surface recombination velocity, density of defect states at the a-Si:H/c-Si hetero-interface and rear side geometry. The influence of these parameters has been tested by generating the current-voltage characteristics under illumination. Results indicate that the key parameters to achieve high efficiency are high c-Si substrate quality, low surface recombination velocity especially at the front surface, and a low recombining a-Si:H/c-Si interface. The width of the gap region (spacing between the back-surface field (BSF) and the emitter) must be kept as small as possible to avoid recombination of minority carriers in the bulk c-Si. For IBC-SiHJ based on n-type c-Si, the optimum geometry corresponds to a minimum size BSF region and a maximum size emitter region while for IBC-SiHJ based on p-type c-Si a BSF width equivalent to around 30% of the pitch is an optimum.