Efficient solar cells with enhanced humidity and heat stability based on benzylammonium-caesium-formamidinium mixed-dimensional perovskites

Perovskite solar cells (PSCs) exhibit remarkable photovoltaic performance with a power conversion efficiency (PCE) over 22%, but they exhibit instability in moist environments and at high temperatures. Compared to 3D perovskites, two-dimensional (2D) layered perovskites display excellent environmental stability but relatively poor photovoltaic performance. Here, we combined 2D/3D perovskites and simultaneously introduced the cesium cation (Cs⁺) to fabricate benzylammonium-caesium-formamidinium mixed-dimensional (MD) perovskite (BE/FA/Cs MD perovskite) solar cells. The BE/FA/Cs MD perovskite device with an optimal benzylammonium content exhibits a PCE as high as 19.24%. The improved PCE of 19.24% (BE/FA/Cs MD, x = 0.05) is attributed to great crystal orientation, outstanding surface quality, superior optical properties and enhanced charge transfer. More importantly, the BE/FA/Cs MD perovskite devices display superior humidity and heat stability. When subjected to 50% relative humidity (RH) for 1600 h and 85 °C for 240 h in the dark, the BE/FA/Cs MD (x = 0.05) devices without encapsulation retain 85% and 83% of their initial PCE, respectively. These results provide us with an important method to obtain highly efficient MD PSCs with long-term stability as a next-generation photovoltaic energy source.