Ultrafast and High-Yield Polaronic Exciton Dissociation in Two-Dimensional Perovskites

Layered two-dimensional (2D) lead halide perovskites are a class of quantum well (QW) materials, holding dramatic potentials for optical and optoelectronic applications. However, the thermally activated exciton dissociation into free carriers in 2D perovskites, a key property that determines their optoelectronic performance, was predicted to be weak due to large exciton binding energy (E-b, about 100-400 meV). Herein, in contrast to the theoretical prediction, we discover an ultrafast (<1.4 ps) and highly efficient (>80%) internal exciton dissociation in (PEA)(2)(MA)(n-1)PbnI3n+1 (PEA = C6H5C2H4NH3+, MA = CH3NH3+, n = 2-4) 2D perovskites despite the large E-b. We demonstrate that the exciton dissociation activity in 2D perovskites is significantly promoted because of the formation of exciton-polarons with considerably reduced exciton binding energy (down to a few tens of millielectronvolts) by the polaronic screening effect. This ultrafast and high-yield exciton dissociation limits the photoluminescence of 2D perovskites but on the other hand well explains their exceptional performance in photovoltaic devices. The finding should represent a common exciton property in the 2D hybrid perovskite family and provide a guideline for their rational applications in light emitting and photovoltaics.

Automated summary

Contrary to theoretical predictions, ultrafast and highly efficient internal exciton dissociation was discovered in 2D lead halide perovskites, attributed to exciton-polarons formation and reduced exciton binding energy by polaronic screening. This unique property limits photoluminescence but explains exceptional performance in photovoltaic devices, offering insights for rational applications in light emitting and photovoltaics within the 2D hybrid perovskite family.