In Situ Dehydration Condensation of Self‐Assembled Molecules Enables Stabilization of CsPbI3 Perovskites for Efficient Photovoltaics

Abstract Inorganic perovskites, with Cs + substituting volatile organic components, show great promise in photovoltaic applications due to their outstanding optoelectronic properties and thermal stability. However, the black‐to‐yellow phase transition of CsPbI 3 remains a challenge for realizing high‐performance inorganic perovskite solar cells (IPSCs). Herein, an effective approach is reported via incorporating the self‐assembled molecule Me‐4PACz to synergistically stabilize the [PbI 6 ] 4− octahedra and form a hydrophobic layer at interface and grain boundaries. An in situ dehydration condensation reaction of Me‐4PACz is observed during film annealing, which favors the reduction of undesired aggregation of Me‐4PACz in humid air, thus leading to enhanced anchoring interaction and more effective hydrophobic protection of CsPbI 3 . Therefore, the air‐processed CsPbI 3 perovskite films show dramatically improved phase purity and humid stability. This strategy also improves the energy level alignment between perovskite and charge transport layers. As a result, a champion efficiency of 20.21% is realized, representing one of the highest reported values for air‐processed inverted IPSCs. Furthermore, it is demonstrated that by combining Me‐4PACz with the previously reported ethacridine lactate (EAL) additive, the device performance can be further boosted to 21.38%, which is a record efficiency for the inverted IPSCs reported to date.