Perovskite Photovoltaics: Pick FAPbI ₃ and Stick to It

The choice of the perovskite composition is pivotal for solar cells. In this Perspective, we argue that, among known perovskite compositions, formamidinium lead iodide (FAPbI 3 ) stands out due to its optimal bandgap, absence of halide segregation observed in mixed-halide alloys, and immunity against oxidation unlike in tin-based perovskites. However, stabilizing the photoactive α-FAPbI 3 remains a major challenge, as it readily transforms into the thermodynamically stable δ-FAPbI 3 at room temperature. In this Perspective, we briefly review the challenges in stabilizing α-FAPbI 3, summarize strategies to address this instability with minimal and no bandgap penalty, and offer our outlook on future directions: (i) stabilization of α-FAPbI 3 without bandgap compromise; (ii) understanding the mechanisms of additive-less stabilized α-FAPbI 3 single-crystal perovskite solar cells (PSCs); (iii) development of all-ambient air fabricated tandem solar cells using α-FAPbI 3 as a narrow-bandgap subcell; and (iv) adoption of only green solvents to enable scalable, sustainable, and widespread manufacturing of perovskite solar modules.