Supporting Data: The effects of junction interdiffusion and misfit dislocations on the efficiency of highly mismatched heterojunction photovoltaic devices

Abstract form paper: A general modelling methodology has been developed to evaluate the effects of chemical interdiffusion and misfit dislocations on the performance of heterojunction solar cells made from highly mismatched materials. Results for the exemplar materials system CdS-CdTe are contrary to the widely held belief that such interdiffusion is beneficial to photovoltaic performance. In the model, recombination is presumed to take place at the cores of misfit dislocations - with the distribution of these dislocations in the interdiffused layer being calculated so as to minimise the total energy (an incidental result shows that the total number of dislocations is independent of the diffusion profile). The model takes calculated chemical profiles, optical absorption and dislocation distributions from which the photovoltaic performance and recombination losses are evaluated. It was shown that for the realistic case in which the interdiffused region does not extend beyond the space charge region, then photovoltage losses dominate over any photocurrent gains. For the case of CdS-CdTe, interdiffusion is always deleterious to performance and this is attributed to the misfit dislocations occupying the space charge region. Methods to engineer mixed junctions that may increase solar conversion efficiency are discussed.