Tailoring Carrier Dynamics by Band Alignment Engineering in Quasi-2D Perovskite LED

Band alignment of semiconductors is a crucial factor in the construction of efficient optoelectronic devices. However, no studies have reported on the impact of the phase distribution in quasi-2D lead halide perovskites on band alignment and carrier dynamics. Herein, an alteration in band alignment is achieved by intentionally optimizing phase distribution in a (PEA) 2 CsPb 2 I 7 quasi-2D film via the addition of a crown ether. It is experimentally evidenced that the band alignment can be engineered from type II to type I for the crown-induced narrowing of the phase distribution, which results in enhanced electron–phonon coupling and increased exciton binding energy. As a consequence, accelerated hot carrier cooling, suppressed Auger recombination, and enhanced exciton recombination are observed in the crown-treated sample. Finally, benefiting from band alignment engineering, the peak external quantum efficiency of the constructed light-emitting diode is improved from 7.4% to 20.1%.