Energy Funneling between Distinct Exciton States in Monophase 2D Lead Halide Hybrid Perovskites Induced by Lattice Distortion

Energy funneling holds strong promise for highly efficient energy conversion and light-emitting devices. Owing to their unmatched structural diversity, lead halide perovskites constitute an ideal platform to explore energy funneling phenomena and applications, a prominent example among which is the mixed-phase, quasi-2D perovskites. Here we report energy funneling between distinct exciton states within nominally phase-pure 2D perovskites, which is induced by lattice distortion that can be quantitatively controlled through organic cations. The existence of two excitonic states with distinct energies is manifested as correlated dual absorption and emission features from room temperature down to 4 K, which is further confirmed by magnetic circular dichroism spectroscopy. Transient absorption measurements reveal sub-picosecond energy funneling from the high-energy exciton to the low-energy exciton, which is also pump power dependent due to the state filling effect. These observations are highly reminiscent of but differ fundamentally from the inter-phase energy funneling in quasi-2D perovskites. Our study opens an additional avenue of controlling energy/charge flow in metal halide perovskites through structural engineering.