Optimization of Selective Contacts in Si Heterojunction Photovoltaic Cells Considering Fermi Level Pinning and Interface Passivation

Semiconducting metal oxides having proper band offset with Si can provide high carrier selective contacts resulting in metal/interlayer/absorber heterojunction solar cell. Previous results showed double heterojunction cell could outperform homojunction cell. Systematic study identifying the design parameters of selective contacts is missing. In this paper, we have identified the design issues for Si heterojunction cell: metal Fermi level pinning, oxide doping and interface passivation. Our simulations show that these issues are important in optimized design of a carrier selective contact. The results suggest that high doping in the oxides and proper choice of metals can compensate for some of the drastic effects of poor interface passivation which is typically a problem observed in these cells. The simulation results are in agreement with experiment. This work will provide a better understanding of the effect of Fermi level pinning in heterojunction cells, which has mostly been ignored by the photovoltaics community, but is becoming increasingly important. We show that a heterojunction cell can replace highly doped emitter and back surface field resulting in high efficiency and low thermal budget fabrication.