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.