Carrier relaxation and exciton dynamics in chemical-vapor-deposited two-dimensional hybrid halide perovskites

Chemical vapor deposition (CVD), without the use of any solvents, is a viable option for the growth of high-quality two-dimensional (2D) Ruddlesden-Popper-type hybrid halide perovskite films. Insights into carrier relaxation and exciton dynamics are crucial for the application of such 2D perovskite films in optoelectronics. By employing broadband transient absorption (TA) spectroscopy and time-resolved photoluminescence, we compare the carrier relaxation and exciton dynamics in two prototypical 2D lead-iodide perovskite systems with butylammonium (BA) and phenylethylammonium (PEA) cations grown by CVD. Along with neat 2D perovskite films, heterojunctions with tin oxide layers were also investigated. The TA peaks show differences in the lifetime and evolution between the two perovskite films and their heterojunction counterparts, providing valuable insights into the structural disparities between these perovskites and the underlying factors governing excitonic dynamics. The TA peak at 530 nm decays faster in PEA2PbI4 compared with BA2PbI4 highlighting the role of the organic cation and the polaronic nature of this peak. Fast carrier cooling times of 150 fs, signaling the absence of any phonon bottleneck effect, are observed. The decay dynamics of the band-edge bleach reveal a strong contribution from the Auger recombination process at early times, when the system is far from equilibrium.