Unveiling hot carrier relaxation and carrier transport mechanisms in quasi-two-dimensional layered perovskites

Quasi-two-dimensional (2D) layered perovskites have lately attracted extensive research interest due to their superior environmental stability to their three-dimensional (3D) counterparts. While solar cells based on 2D layered perovskites have achieved remarkably high efficiencies over 18%, their intrinsic carrier dynamics after photoexcitation remain obscure due to the presence of bound excitons and the coexistence of multiple layered perovskite phases. Discrepancies were found in the interpretations of the reported ultrafast processes with hundreds of femto- or pico-second time scales in previous literature via transient absorption measurements. Here, carrier dynamics in (PEA)2(MA)2Pb3I10 (PEA = C6H5(CH2)2NH3; MA = CH3NH3) 2D layered perovskite was systematically studied through a combination of transient absorption and time-resolved photoluminescence measurements with femtosecond time resolution. The ultrafast sub-ps (100–400 fs) carrier dynamics is unambiguously demonstrated due to hot carrier relaxation. Carrier transport occurs from small n layered perovskites to their surrounding 3D like (large n) perovskite via energy transfer on the time scale of 2–300 ps. These results provide valuable information on the intrinsic carrier dynamics in 2D layered perovskites which would be helpful in further improving the device performance.