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.