Quasi-2D Perovskite with Symmetrical n Value Interface Enables a Certified Efficiency over 21.5%

Quasi-2D perovskite exhibits superior environmental stability due to the prevention of moisture and oxygen infiltration and the formation barrier for ion vacancy, ascribed to the hydrophobic large organic cation, and has the potential to enhance the stability of resulting solar cells. However, attributed to the unoptimized quantum well distribution, crystal orientation, and low carrier mobility, the power conversion efficiency of quasi-2D perovskite solar cells still lags far behind that of pure 3D perovskite-based devices. Here we elucidate that by adding MAPbCl3 (MA: methylammonium) as the nucleation core and extra MACl as crystal orientation modulation additive, a highly crystalline quasi-2D perovskite with a symmetrical and preferential crystal orientation low-n value interface could be obtained. This FA (formamidinium)-based quasi-2D perovskite solar cells show a champion efficiency of 21.96% (certified 21.56%) as well as 19.20% for a large area (1 cm2) device, which is among the best-reported efficiencies for quasi-2D Ruddlesden–Popper perovskite solar cells.