Chemical Interaction at the MoO3 CH3NH3PbI3 xClx Interface

The limited long term stability of metal halide perovskite based solar cells is a bottleneck in their drive toward widespread commercial adaptation. The organic hole transport materials HTMs have been implicated in the degradation, and metal oxide layers are proposed as alternatives. One of the most prominent metal oxide HTM in organic photovoltaics is MoO3. However, the use of MoO3 as HTM in metal halide perovskite based devices causes a severe solar cell deterioration. Thus, the formation of the MoO3 CH3NH3PbI3 xClx MAPbI3 xClx heterojunction is systematically studied by synchrotron based hard X ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X ray spectroscopy, and Raman spectroscopy. Upon MoO3 deposition, significant chemical interaction is induced at the MoO3 MAPbI3 xClx interface substoichiometric molybdenum oxide is present, and the perovskite decomposes in the proximity of the interface, leading to accumulation of PbI2 on the MoO3 cover layer. Furthermore, we find evidence for the formation of new compounds such as PbMoO4, PbN2O2, and PbO as a result of the MAPbI3 xClx decomposition and suggest chemical reaction pathways to describe the underlying mechanism. These findings suggest that the direct MoO3 MAPbI3 xClx interface may be inherently unstable. It provides an explanation for the low power conversion efficiencies of metal halide perovskite solar cells that use MoO3 as a hole transport material and in which there is a direct contact between MoO3 and perovskit