Suppressing the phase separation in FAMA mixed perovskite solar cells via the preloading of A site cations within the lattice

The incorporation of MA as a dopant is highly advantageous for stabilizing the lattice structure of α-phase FAPbI3. However, achieving a homogeneous phase mixing is only feasible at elevated MA doping levels, which significantly compromises both the efficiency and stability of FA-dominated perovskite solar cells (PSCs). In this study, it is found that in the nucleation stage of FAMA mixed perovskite, MA+ exhibit a significant kinetic advantage over FA+ in their reaction with PbI3−. The rapid crystallization of MAPbI3 not only induces FA-MA separation but also hinders the crystallization of perovskite due to strains induced by the bulky FA+ cations. To address this issue, we introduced FA0.8MA0.2PbI3 single crystals as the material source to prepare the precursor solutions, which achieved a delicate balance between lattice stability and bandgap (Eg = 1.54 eV). The preloaded A-site cations within the PbI3− cages make the bare FA-dominated perovskite films by blade coating maintain the phase stability in wild ambient for over one year. The final PSCs (0.09 cm2) achieved a highest power conversion efficiency (PCE) of 23.66 %, among the highest efficiency records for blade coated PSCs. The unpackaged PSCs show efficiency loss of < 10 % as being aged in air with a relative humidity of 10 % for over 1000 h.