Additive‐Free Spiro‐OMeTAD@P3HT Composite/NiOx Hole‐Transporting Bilayer for Efficient (19%), Stable, and Fully Solution‐Processed Carbon‐Electrode‐Based Perovskite Solar Cells

Hole‐transporting layer (HTL) plays a critical role in determining the device performance of carbon‐electrode‐based perovskite solar cells (C‐PSCs). However, the use of best‐performing organic HTL (such as 2,2′,7,7′‐tetrakis (N, N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene [Spiro‐OMeTAD] or poly(3‐hexylthiophene) [P3HT]) for efficient and stable C‐PSCs remains challenging due to the hygroscopic additives, unfavorable band alignments, and corrosive carbon pastes. Herein, the additive‐free Spiro‐OMeTAD/P3HT composite (denoted as Spiro@P3HT) is employed as HTL to construct the fully ambient solution‐processed C‐PSCs, and NiO x is used as top HTL/buffer layer that protects P3HT from being corroded by carbon pastes. As compared to pristine P3HT, the incorporation of Spiro‐OMeTAD not only smooths the HTL morphology, but also shifts down the highest occupied molecular orbital level, thus forming a more energy‐favorable cascade that maximizes hole extraction at the perovskite/HTL interface and minimizes recombination loss. Consequently, the target C‐PSCs with optimal Spiro@P3HT composite HTL achieve a champion efficiency of 19%. More importantly, benefiting from the self‐sealing protection of hydrophobic Spiro@P3HT HTL and carbon electrode, the target C‐PSCs exhibit no noticeable performance degradation after storage in ambient air for 1440 h and continuous operation under illumination for 350 h. In this work, a facile way is provided to develop robust and efficient additive‐free HTL toward fully solution‐processing high‐performance C‐PSCs.