The Influence of Conduction Band Offset on CdTe Solar Cells

Numerical modeling of conduction band offset (ΔE C) between an n-type CdSO window layer and a p-type CdTe absorption layer on the effect of the cadmium telluride (CdTe) solar cells was studied through simulation. The simulation results show that a slightly positive ΔE C yields high efficiency because the surface recombination rate at the CdSO/CdTe interface can be substantially reduced, leading to higher open-circuit voltage (V OC) and fill factor. Further increase in ΔE C (≥ 0.4 eV) will impose an energy barrier against the photo-generated electrons under forward bias. We demonstrated the mechanistic picture of this effect using thermionic emission. However, if intra-band tunneling is considered in the simulation, a large ΔE C shows negligible influence on the performance of CdTe solar cells. Our simulation results suggest that an ΔE C of 0.3 eV is an optimal conduction band offset for high-efficiency CdTe solar cells.