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Role of halide anions in perovskite/graphene oxide photovoltaics

Smart device designs with cheap materials and simple processing methods are necessary for cost-effective and efficient solar cell manufacturing. Methylammonium lead halides (MAPbTx, T = I, Br, Cl) perovskites are promising photovoltaic materials, with high power conversion efficiency (PCE>22%). Perovskite instability, however, has been one of the major obstacles for achieving device performance. Another challenge is the uncontrolled chemistry at the interfaces of the electron/hole transporting layers that limit device function. In order to facilitate an efficient charge transport, graphene-derived nanomaterials made from graphene oxide (GO) and reduced graphene oxide (RGO) have replaced metal oxides and polymers. Overcoming the variation in PCE due to the presence of defects at the interfaces of GO and MAPbTx remains a challenge. Therefore, understanding the fundamental nature of defects is necessary to identify the root cause of device performance failure. In order to investigate interfacial defect modification, we utilize an in situ spectroscopy characterization approach to study chemical interactions at GO/MAPbTx interfaces. We find that halide anions of the perovskite precursors determine defect nucleation in GO, and thereby the growth mechanism. These results demonstrate the need for interface characterization to improve the reliability of perovskite photovoltaics.