Dual benefits from “wiring” charge-transfer moieties to perovskite surfaces

Abstract

The field of perovskite photovoltaics has seen unprecedented developments, driving a sevenfold increase in power-conversion efficiency since 2009. This growth testifies to the broad potential impacts of these materials. While solvent polarity enhances charge separation (CS) and the rate of charge transfer (CT) leading to CS, the instability of these perovskites in polar environments hampers the realization of their potential. Focusing on interfacial CT in nonpolar environments, here we demonstrate the importance of binding a redox-active moiety to cesium tribromoplumbate(II), or cesium lead tribromide (CsPbBr₃), perovskite nanocrystals (NCs) for achieving efficient CT in hydrocarbon media. Tight-binding compounds, such as amines, etch such low-valency perovskites. At controlled concentrations, however, binding an amine derivative of a phenothiazine electron donor to NC surfaces not only provides electronic coupling for efficient CT but also eliminates sites responsible for undesired exciton deactivation. This dual benefit from “wiring” CT mediators to perovskite surfaces ensures efficient charge extraction in nonpolar media, providing a key paradigm for interfacing these optoelectronic materials with an organic phase.