Crystal Engineering of a Two-Dimensional Lead-Free Perovskite with Functional Organic Cations by Second-Sphere Coordination.

Hybrid lead halide perovskite semiconductors are attracting increasing attention for applications in optoelectronics. However, the high lead content calls for the development of greener and smarter alternatives through crystal engineering. This is extremely challenging since the use of functional cations often results in the disruption of the metal halide framework. Here we show the rational design of a new lead-free, copper-based hybrid perovskite following a second-sphere coordination approach. Our synthetic strategy allows the incorporation of an organic cationic fluorophore within the two-dimensional Cu-Cl framework of a layered copper perovskite. The functionalization results in a moisture-stable and near-UV/blue-emitting copper perovskite. Along with the possibility of extending the emission in the visible range by further synthetic design, our approach paves the way for the development of a new class of Pb-free perovskites with potential applications in solid-state lighting.