Ab initio study of electron and hole transport in pure and doped MnO and MnO:ZnO alloy

Abstract

Rationally engineering photocatalytic devices that power water splitting or CO₂ reduction reactions requires identifying economical materials that efficiently absorb sunlight and have suitable band edge placements. Recent theoretical investigations have predicted that a 1 : 1 alloy of MnO and ZnO meets these criteria. However, poor hole conductivity in undoped MnO:ZnO alloys (with up to 10% ZnO) severely limits this material's utility in electronic devices, and its electron conductivity has not yet been characterized. Here we investigate carrier transport in pure and doped MnO and MnO:ZnO with ab initio quantum chemistry calculations. Electrostatically embedded clusters are used to compute and compare relative electron/hole transfer barriers within the small polaron model. We assess the effects of Al, Ga, In, Sc, Y, Ti, Sb, Gd, F (n-type dopants) and Li (a p-type dopant) to determine which may enhance conductivity in MnO:ZnO. Our findings indicate that Ga, Sc, Ti, F, and Sb dopants create deep traps whereas In forms shallower traps that merit further investigation. Y, Al, Gd, and Li dopants should increase the carrier concentration while maintaining favorable electron and hole transport pathways. The latter are recommended for increasing the conductivity of MnO:ZnO and its effectiveness for solar energy conversion.