In Situ Reconstruction Post‐Treatment for Efficient Carbon‐Based Hole‐Conductor‐Free Printable Mesoscopic Perovskite Solar Cells

Abstract Perovskite solar cells are regarded as the most promising and disruptive photovoltaic of the new generation. Carbon‐based hole‐conductor‐free printable mesoscopic perovskite solar cells (p‐MPSCs) with three mesoscopic layers have garnered considerable interest owing to their simple manufacturing process and cost‐effective raw materials, signaling the potential for commercialization. However, the energy level mismatch between the perovskite and the carbon electrode as well as defects at perovskite grain boundaries inevitably lead to additional non‐radiative carrier recombination and large voltage loss. In this study, a facile in situ reconstruction post‐treatment approach is employed to integrate lead sulfide (PbS) and the two‐dimensional (2D) perovskite K 2 PbI 4 into the mesoporous scaffolds of p‐MPSCs. In this way, grain boundary defects are effectively passivated and the ion migration is suppressed by introducing 2D perovskite K 2 PbI 4 at grain boundaries. Besides, the incorporation of PbS leads to the downward shift of the Fermi level for perovskite, which enhances hole collection within the device by optimizing band alignment at the perovskite/carbon interface. Consequently, an improved efficiency exceeding 20% is achieved for p‐MPSCs with no significant performance degradation observed over a storage period of 235 days. This strategy provides a facile and novel approach toward fabricating highly efficient and stable p‐MPSCs.