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 (FAPbI3) 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-FAPbI3 remains a major challenge, as it readily transforms into the thermodynamically stable δ-FAPbI3 at room temperature. In this Perspective, we briefly review the challenges in stabilizing α-FAPbI3, summarize strategies to address this instability with minimal and no bandgap penalty, and offer our outlook on future directions: (i) stabilization of α-FAPbI3 without bandgap compromise; (ii) understanding the mechanisms of additive-less stabilized α-FAPbI3 single-crystal perovskite solar cells (PSCs); (iii) development of all-ambient air fabricated tandem solar cells using α-FAPbI3 as a narrow-bandgap subcell; and (iv) adoption of only green solvents to enable scalable, sustainable, and widespread manufacturing of perovskite solar modules.