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

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 CsPbI₃ 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 [PbI₆]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 CsPbI₃. Therefore, the air-processed CsPbI₃ 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.