Screening procedure for structurally and electronically matched contact layers for high-performance solar cells: Hybrid perovskites

The rapid progress in performance of solar cells based on hybrid halide perovskites means that devices based on these materials have reached a stage where research interest can now focus on development of robust technology. One of the key questions relating to these (and indeed any) devices is their lifetime and stability which in turn is often influenced by the quality of interfaces and junctions within the device. In this study we present a methodology which allows screening for mechanically stable, electronically suitable interface combinations-applying the technique to screen 175 common semiconductors for viability as electron and hole extracting contacts for CH₃NH₃PbI₃. The screening method can be applied to any semiconductor junction problem and relies on easily obtained experimental or theoretical information-electron affinity, ionisation potential, lattice parameters and crystal structure. From the screening we rank the candidates according to a figure of merit, which accounts for band alignment and chemical/mechanical stability of the interface. Our screening predicts stable interfaces with commonly applied electron extraction layers such as TiO₂ and ZnO as well giving insight into the optimal polymorphs, surfaces and morphologies for achieving good quality contacts. Finally we also predict potentially effective new hole and electron extraction layers, namely Cu₂O, FeO, SiC, GaN, and ZnTe.