Formamidinium-incorporated Dion-Jacobson phase 2D perovskites for highly efficient and stable photovoltaics

Dion-Jacobson phase two-dimensional (DJ 2D) perovskites, recently attracting considerable interests, exhibit excellent environmental stability and structural tunability, but their solar cells still offer unsatisfactory power conversion efficiencies (PCEs). Herein, we develop DJ 2D perovskites employing formamidinium (FA+) as a ternary cation in the perovskite cages ((PDA)(FA)x(MA)3−xPb4I13, x = 0, 0.15, 0.3 and 0.6, PDA = 1,3-propanediammonium) for highly efficient and stable perovskite solar cells (PSCs). We found that the DJ 2D perovskite with a 10% FA+ fraction presents improved crystallinity, preferred vertical orientation, and longer charge carrier lifetime compared to that without FA+ doping. As a result, the FA-doped DJ 2D PSCs exhibit a champion PCE of 14.74% with superior device stability. The unencapsulated devices sustain over 92% of its initial PCE after storage at a constant relative humidity (RH) of 65% for 6000 h, 90% by heat at 85 °C in air for 800 h, and 94% under 1-sun illumination for 5000 h. These findings demonstrate that the incorporation of FA cation into the DJ 2D perovskite is a promising strategy to develop highly efficient and stable DJ 2D PSCs.