Constructing Graded Perovskite Homojunctions by Adding Large Radius Phenylmethylamine Ions for Sequential Spin-Coating Deposition Method To Improve the Efficiency of Perovskite Solar Cells

Cs/FA/MA triple cation perovskite films have been well developed in the antisolvent dripping method due to its outstanding photovoltaic and stability performances. This work constructs a quadruple-cation perovskite solar cell for the sequential spin-coating deposition method. The phenylmethylamine ions (PMA+) with a larger ionic radius than formamidine ions (FA+) and methylamine ions (MA+) ions are introduced in Cs/FA/MA perovskite to obtain quasi-2D PMA/Cs/FA/MA perovskite. The quasi-2D PMA/Cs/FA/MA and 3D Cs/FA/MA perovskite formed many graded perovskite homojunctions in the perovskite layer. It promotes the separation and migration of photogenic carriers due to heterojunction energy levels and improves the short-circuit current density and filling factor of the perovskite solar cells. The quadruple-cation perovskite solar cells with 2% PMAI obtain a max power conversion effciency (PCE) of 22.0% and improve the stability of the device because the hydrophobic phenylmethyl group can effectively reduce the water gas into perovskite.