Achieving high open circuit voltage for hole transport layer free ambient perovskite solar cells utilizing electric double layer effect

One of the features of perovskite solar cells (PSCs) that make them stand out among all photovoltaics (PVs) is their high open-circuit voltage (VOC). Owing to their simple manufacturing process, low cost of components, and good stability, carbon electrode-based metal-halide PSCs are gaining interest for their better stability and low cost than noble metal electrodes. However, carbon electrode-based hybrid PSCs suffer low open-circuit voltage (VOC). This work demonstrated the fabrication of ambient processed hybrid perovskite solar cells using low-temperature curable carbon-based electrodes without a hole transport layer. The devices exhibit an impressive high open circuit voltage of 1.07 V, even without a dedicated hole transport layer. The photovoltaic performance was further investigated with the same perovskite absorber, synthesized by solution-processed and solid-state synthesis routes. The latter have yielded better short circuit current and power conversion efficiency due to perovskite's lesser built-in trap density. Furthermore, using a combined ionic electronic carrier transport model, an electric double-layer formation was ensured across the perovskite/carbon interface and accumulating halide vacancies at the perovskite/TiO2 interface can effectively reduce carrier recombination and boost the device's VOC. This study envisages the impact of the electric double layer in free carrier transport of an ionic-electronic semiconductor like hybrid perovskites and can pave the way to improve the open-circuit voltage of carbon-based perovskite solar cells.