Establishing charge-transfer excitons in 2D perovskite heterostructures

Charge-transfer excitons (CTEs) immensely enrich property-tuning capabilities of semiconducting materials. However, such concept has been remaining as unexplored topic within halide perovskite structures. Here, we report that CTEs can be effectively formed in heterostructured 2D perovskites prepared by mixing PEA(2)PbI(4):PEA(2)SnI(4), functioning as host and guest components. Remarkably, a broad emission can be demonstrated with quick formation of 3 ps but prolonged lifetime of ~0.5 μs. This broad PL presents the hypothesis of CTEs, verified by the exclusion of lattice distortion and doping effects through demonstrating double-layered PEA(2)PbI(4)/PEA(2)SnI(4) heterostructure when shearing-away PEA(2)SnI(4) film onto the surface of PEA(2)PbI(4) film by using hand-finger pressing method. The below-bandgap photocurrent indicates that CTEs are vital states formed at PEA(2)PbI(4):PEA(2)SnI(4) interfaces in 2D perovskite heterostructures. Electroluminescence shows that CTEs can be directly formed with electrically injected carriers in perovskite LEDs. Clearly, the CTEs presents a new mechanism to advance the multifunctionalities in 2D perovskites.