Activating Old Materials with New Architecture: Boosting Performance of Perovskite Solar Cells with H(2)O‐Assisted Hierarchical Electron Transporting Layers

The breakthrough of organometal halide perovskite solar cells (PSCs) based on mesostructured composites is regarded as a viable member of next generation photovoltaics. In high efficiency PSCs, it is crucial to finely optimize the charge dynamics and optical properties matching between the perovskites and electron transporting materials to relax the trade‐off between the optical and electrical requirements. Here, a simple antipolar route with H(2)O as the additive is proposed to prepare hierarchical electron transporting layers to boost the efficiency of dopant‐free PSCs. The photovoltaic performance of the PSCs is enhanced owing to increased light‐scattering, improved Ostwald ripening, and photo‐generated electron extraction. Optimization of the H(2)O addition enables a valid power conversion efficiency of 19.9% (reverse scan: 20.02%) to be achieved. The device can retain more than 90% of its initial performance after storage in air more than 30 days. These results are inspiring in that they present that a mesoporous transporting layer could be easily re‐constructed to hierarchical architecture by the antipolar method to further improve the performance of PSCs.