Dimension engineering on cesium lead iodide for efficient and stable perovskite solar cells

Cesium lead iodide perovskite (CsPbI3) has been proposed as an efficient alternative to modify the instability of methylammonium lead iodide (MAPbI(3)) under thermal and humidity stress. However, three-dimensional (3D) cesium lead iodide forms an undesirable non-perovskite structure with a wide bandgap at ambient atmosphere. Herein, dimension engineering is employed by introducing a bulky ammonium cation to form stable 2D cesium lead iodide perovskite BA(2)CsPb(2)I(7) (BA = CH3(CH2)(3)NH3), which not only exhibits prominent optoelectronic properties, but also possesses superior structural and compositional stability to 3D CsPbI3 and MAPbI(3) under the pressure of heat and humidity. The current 2D BA(2)CsPb(2)I(7) shows excellent stability after exposure to 30% relative humidity for 30 days or upon heating at 85 degrees C for 3 days. In addition, the corresponding BA(2)CsPb(2)I(7) based planar perovskite solar cells retain 92% of the initial power conversion efficiency (PCE) after aging for over 30 days without any encapsulation, demonstrating the up- scalability of 2D perovskite compounds as stable and efficient light- absorbing materials for perovskite solar cells and other optoelectronic applications.