Molecular Design Strategy for Meta‐Substituted Aromatic Organic Halides in Zero‐Lead‐Release Halide Perovskites with Efficient Waterproof Light Emission

Abstract Halide perovskites have received an immense attention in the field of optoelectronics due to their outstanding photophysical properties. But so far, lead‐based halide perovskites still account for most of the research, which raises concerns due to lead toxicity. Herein, a new design strategy is proposed utilizing a super large, energetically higher singlet and triplet energy levels aromatic organic cation to incorporate into the perovskite structure, forming ultra‐stable high‐performance 2D/3D (quasi‐2D) perovskite. The judicious molecular design of connecting all the phenyl groups at their meta sites ensures the simultaneous achievement of a large molecular weight and high singlet and triplet energy levels. The resulting quasi‐2D perovskite thin films not only exhibits excellent emission properties but also, surprisingly, show long‐term waterproof‐level stability. The robustness of these perovskites is confirmed by their extraordinary emission stability upon direct water immersion and almost undetectable lead release in water. Proof‐of‐concept of a water‐resistant color conversion‐type perovskite near‐infrared (NIR) light‐emitting diode (LED) is demonstrated, showing high external quantum efficiency (EQE) and power conversion efficiency (PCE) of 20.5% and 13.3%, respectively. It is believed these results and strategy pave a new way for realizing environmentally friendly lead halide materials and devices.