Cost-efficient clamping solar cells using candle soot for hole extraction from ambipolar perovskites

Ambient-unstable hole transporters and expensive and complicated noble metal electrode deposition are incompatible with the large scale and low-cost production of perovskite solar cells and thus would hamper their commercialization. Herein we report a new modality of perovskite solar cells that do away with the use of conventional hole transporters by directly clamping a selective hole extraction electrode made of candle soot and a deliberately engineered perovskite photoanode. The key soot/perovskite interface, which promotes hole extraction and electron blocking by forming a Schottky junction, was established seamlessly by pre-wetting and reaction embedding the carbon particles. Femtosecond time-resolved photoluminescence revealed a high hole extraction rate at 1.92 ns^-1. We have now achieved 11.02% efficiency, making an important step towards roll-to-roll production of perovskite solar cells.