Ultrafast directional hot carrier transfer in bilayer perovskite heterojunctions

Hot carrier dynamics in semiconductors govern unique mechanisms in high-performance devices with potential to exceed thermodynamic limits of optoelectronic device efficiency. Here, we report ultrafast directional transfer of hot carriers within laminated bilayer CsPbBr₃/FAPbBr₃ perovskite heterojunctions. Using ultrafast spectroscopy, we show that hot carriers generated in the FAPbBr₃ layer are directed to the CsPbBr₃ layer within picoseconds. This process is driven by differences in cooling pathways that create density gradients for directional hot carrier transfer. Such ultrafast hot carrier inter-junction transfer boosts the carrier density in CsPbBr₃ layer to the level of population inversion. By fabricating perovskite heterojunction vertical-cavity surface-emitting lasers, we achieve hot-carrier laser devices with threshold down to 1.4 μJ cm^-2 under nanosecond pulsed excitation, five times lower than that of individual perovskite layers. Our findings establish hot carrier transfer in hybrid perovskites as a promising strategy for high-performance hot-carrier lasers, ultrafast laser diodes, and photodetectors.