Stabilizer-free pure α-phase FAPbI3 perovskite through seed-assisted growth yields efficient photovoltaics.

The α-phase of formamidinium lead iodide (α-FAPbI3) perovskite has a promising bandgap for efficient single-junction photovoltaics. However, its large A-site FA+ cation destabilizes the perovskite lattice, favoring transformation into non-perovskite δ-phases under ambient conditions. To overcome this instability, compositional A-site engineering with Cs+, Rb+, and MA+ has been widely explored, but such α-FAPbI3 stabilizers inherently alter the bandgap and complicate crystallization dynamics. Here, we report an α-FAPbI3 stabilizer-free seeded growth strategy that directly incorporates FAPbI3 seeds (SDs) into the PbI2 precursor, lowering, in this way, the nucleation barrier and guiding directional crystallization. Multiscale simulations showed that the persistent structural characteristics of the dissolving SDs pertain more to the α-phase thereby promoting growth of the photoactive α-phase while suppressing the formation of the competing photoinactive δ-phase. This approach yields highly crystalline films with compact morphology and markedly reduced surface roughness, as confirmed by SEM, AFM, and XRD analyses. Electroluminescence measurements (EL) and optical-electrical device simulations reveal that the combined effects of enhanced carrier lifetime and improved charge transport suppress non-radiative recombination, translating into a champion PCE of 23.51% (compared to a 15.5% PCE for the SD-free device). Importantly, the seeded devices preserve 99% of their initial performance after 3000 h under ambient conditions and one sun illumination at 35 ± 5 °C without encapsulation, whereas control devices rapidly degrade, exhibiting a 15% drop in PCE under identical conditions. Our comprehensive investigation concluded that these results establish seeded growth as a practical and effective pathway for realizing efficient and durable FAPbI3-based solar cells without the need for additional α-phase stabilizers, redefining the potential of FA-based perovskite via seeded growth strategy.