Self‐Assembled Molecules Fostering Ordered Spatial Heterogeneity for Efficient Ruddlesden‐Popper Perovskite Solar Cells

Abstract 2D Ruddlesden‐Popper perovskites (RPP) with formamidinium‐cesium (FAC) alloyed cations possess powerful thermal‐moisture stability. However, their photovoltaic performance is hindered by the elusive spatial heterogeneity at multiscale lengths, highly associated with their coupled charge selective contacts. Herein, it reports on how the rational formation of self‐assembly molecules (SAMs) govern the orderliness of the spatial heterogeneity and crystal growth model in FACs‐RPP films, which is proposed to dictate the charge‐carrier dynamics. Unlike the disordered RPP film driven by the amorphous polymeric contacts, the laterally ordered crystallized SAM contacts facilitate a spatially ordered 2D/3D heterogeneity of FACs‐RPP film in long range, where distinct minor 2D phases are tightly coupled in short range. Such ordered heterogeneity can improve the energy transfer efficiency, facilitating the charge‐carrier dynamics in a well‐aligned 2D/3D landscape is discovered. Finally, the champion solar cells using selective SAM‐based FACs‐RPP films ( n = 5) yield an efficiency of 18.85% (certified 18.19%) and excellent damp‐heat/operational stability, ranking in the top league of reported 2D RPP solar cells. More importantly, this SAM‐based principle can be adapted to diverse 2D structures, active areas, and substrate types. This work provides design directions for leveraging bottom‐selective contacts to tune spatial heterogeneity in state‐of‐the‐art 2D RPP optoelectronics.