Conjugated molecular wires on indium-tin oxide: investigation of the electron transfer mechanism and application in tin perovskite solar cells

Electron transfer through ‘molecular wires’ underpins numerous research fields, ranging from single molecule electronics to fundamental biological processes and their application in (bio)electrocatalysis. Here, we report a series of 1-3 nm long conjugated molecular wires, anchored to indium tin oxide (ITO) electrodes, that exhibit a hopping electron transfer (ET) mechanism (with a β value of 0.043 Å⁻¹) previously unknown over these relatively short distances. We show that the nature of the electrode induces a change in the ET mechanism from tunneling to hopping, by reducing the energy gap between the electron donor and acceptor. The applicability of these anchored molecular wires was demonstrated in a tin perovskite solar cell as hole-selective contacts, leading to solar to electrical power conversion efficiency approaching 10% with improved stability under ambient environmental conditions. This work not only opens new avenues for mechanistic investigations of electron transfer using molecular wires, but also showcases their potential impact in applications e.g. in a solar cell.