Recent progress in two‐step fabricated perovskite solar cells using additive engineering

Abstract Two‐step sequential deposition has gained attention as a scalable and reproducible method for fabricating high‐efficiency perovskite solar cells (PSCs). Unlike one‐step methods, this approach allows better control over crystallization kinetics and layer‐by‐layer conversion. However, critical issues such as incomplete conversion of PbI 2 into the perovskites, formation of buried interface defects, poor film uniformity, and residual lattice strain still limit device performance and long‐term stability. To address these challenges, recent research has focused on additive engineering as a versatile and effective solution for two‐step fabricated PSC and has enabled a rapid increase in device performance. This review discusses key additive strategies causing several positive effects to enhance both efficiencies and stabilities of PSCs: (1) inducing porous and disordered PbI 2 structures to promote the diffusion of organic halide salts and enable complete conversion into the perovskites, (2) controlling facet orientation to improve charge transport and moisture stability, (3) buried interface passivation to eliminate voids and defects of the hidden surface, and (4) strain engineering to relieve strain stress during the formation of the perovskite layer. Taken together, this additive engineering has enabled PSCs fabricated via two‐step deposition to reach power conversion efficiencies exceeding 26%, while also enhancing environmental stability. This review provides a clear look at how specific additive chemistry can control crystal growth, improve interface quality, and control lattice strain, giving straightforward guidelines for designing the next generation of two‐step fabricated PSCs.