Simulation of a-Si/c-GaAs/c-Si Heterojunction Solar Cells

In this paper we investigate the performance of thin film a-Si(n+)/c-GaAs(p)/c-Si(p+) heterojunction solar cells by TCAD simulation. The effects of minority carrier lifetime and GaAs layer thickness have been studied. For comparison, a-Si/c-Si based solar cell was also simulated. The results show that for lifetimes larger than 1micro-s, the Voc is 0.8V for GaAs and 0.68V for the c-Si cell. While for lifetimes less than 1micro-s, the Voc still remains 0.8V for GaAs but drops to 0.4V for the c-Si cell. In addition, the Jsc for the GaAs cell is about 1.4mA/cm² larger than the c-Si cell for the 2μm case and it is independent of lifetime for both cells. As a result, the efficiency of the 2μm GaAs solar cell is 3.78% more than the c-Si cell for lifetime=1μs. The effect of GaAs and c-Si absorber layer thickness is also studied. The difference in Jsc between GaAs and c-Si solar cell is larger for thinner solar cells. This bodes well for thin film GaAs based solar cells.