Surface modification and stoichiometry control of Cu2O/SnO2 heterojunction solar cell by an ultrathin MgO tunneling layer

Here, we demonstrated the potential of an ultrathin Mg-rich MgO tunneling layer as a passivation layer for earth-abundant Cu2O based solar cell. An ultrathin Mg-rich MgO layer was introduced to the interface of Cu2O/SnO2 heterojunction by electron beam evaporation, which greatly enhanced the efficiency of Cu2O/SnO2 heterojunction solar cell. The MgO layer was found to significantly reduce the CuO defect density and create a stoichiometry Cu2O surface confirmed by high-resolution X-ray photoelectron spectroscopy. Thus, charge recombination caused by interface defect was mitigated bringing an increased device efficiency. This work highlights the need for stoichiometric Cu2O surface in Cu2O-based solar cells.