Additive Engineering Toward High-Performance CsPbI₃ Perovskite Solar Cells

All-inorganic perovskite solar cells (PSCs) have attracted a lot of attention in the past few years because of their preeminent thermal stability compared with organic–inorganic hybrid PSCs. Among all kinds of all-inorganic perovskites, CsPbI₃ perovskite with a proper bandgap of ≈1.7 eV becomes the most competitive candidate. However, its poor phase stability, hydrophobicity, and high-density defects have limited the development of CsPbI₃ PSCs. To overcome these obstacles for achieving high-performance CsPbI₃ PSCs, additive engineering has been widely used, which has rapidly promoted the power conversion efficiency (PCE) to over 19%. Herein, the progress of additive engineering in CsPbI₃ PSCs is systematically reviewed. First, the roles of additives in CsPbI₃ PSCs are introduced, including improving phase stability, increasing moisture resistance, and passivating defects. Then, the additive engineering is categorized (additive engineering in perovskites and at perovskite/hole transport layer interfaces) and reviewed in detail. Finally, future research directions on additive engineering are suggested for further enhancing stability and improving PCE.