Octahedral Tilt Enables Efficient and Stable Fully Vapor‐Deposited Perovskite/Silicon Tandem Cells

Abstract Thermal evaporation can significantly facilitate scalable, uniform, and conformal perovskite film, particularly well‐suited for the preparation of perovskite/silicon (Si) tandem solar cells . However, the perovskite material easily induces a phase transition from a photoactive phase to a photoinactive phase, limiting the development of the stability and efficiency of tandem cells. Introducing lead chloride (PbCl 2 ) into wide‐bandgap perovskite materials is beneficial for the fabrication of efficient and stable light‐absorbing materials, but the microscopic mechanism of the effect of PbCl 2 on perovskite is still unclear. The study here reports evidences that the addition of PbCl 2 to improve perovskite film stability and optoelectronic performance is due to the minor octahedral tilting of the perovskite structure are reported. It also demonstrates that this strategy accelerates interfacial charge transfer and carrier diffusion in the perovskite bulk and heterojunction interfaces. Therefore, the wide‐bandgap perovskite solar cells (PSCs) prepared by adding PbCl 2 exhibit a champion power conversion efficiency (PCE) of 17.80%. The PSCs retain 97% of their performance following 200 h of operation at the maximum power point under full 1‐sun illumination. Finally, monolithic perovskite/Si tandem cells with record PCEs of 27.43% and an open‐circuit voltage of 1.817 V are fabricated.