Additive Engineering of Sequentially Evaporated FAPbI3 Solar Cells

Abstract Despite the tremendous progress made in the field of perovskite solar cells, their commercialization remains hindered by several challenges, including scalability, stability, and sustainability. Thermal evaporation is a solvent‐free, scalable, and industrially relevant method, yet despite its many advantages, this method is limited by the lack of additive engineering strategies for controlling the growth of perovskite layers. Here, a novel additive engineering strategy is reported that enables the complete conversion of precursors to a perovskite phase during the two‐step deposition of formamidinium lead triiodide (FAPbI 3 ). The approach is based on the co‐evaporation of potassium‐containing additives (KI and KSCN) alongside PbI 2 during the first deposition step, followed by the evaporation of formamidinium iodide. It is demonstrated that the absence of additives leads to an incomplete conversion with a substantial amount of unconverted PbI 2 remaining at the buried interface. On the other hand, the co‐evaporation of the additives improves the conversion process, leading, in the case of KSCN, to phase‐pure α‐FAPbI 3 with improved microstructure. The additive‐engineered p‐i‐n devices achieve efficiencies up to 18.34%, among the highest reported for evaporated FAPbI 3 solar cells without interfacial passivation. This work highlights the great potential of additive engineering for controlling the film formation of thermally evaporated perovskites.