Study of Surface and Bulk Recombination Kinetics of Two-Dimensional Inorganic–Organic Hybrid Semiconductors under Linear and Nonlinear Femtosecond Transient Absorption Analysis

Photo-generated charge carrier dynamics in two-dimensional layered inorganic–organic hybrid semiconductor have been presented utilizing linear and nonlinear femtosecond transient absorption spectroscopy. A weak van der Waals interlayer force mediated self-assembled system (C₆H₉C₂H₄-NH₃)₂PbI₄ shows strong room-temperature exciton absorption at about 507 nm. A systematic study of these exciton carrier cooling dynamics and electron–hole recombination mechanisms from ultrafast broadband transient absorption have been presented with varying injection carrier densities of one-photon (350 nm), two-photon (800 nm), and three-photon (1020 nm) excitations. The demonstrated linear (one-photon) and nonlinear (two- and three-photon) transient absorption studies reveal more clarity on hot-carrier relaxations from surface and bulk exciton states. Fluence-dependent studies clearly demonstrate the hot phonon bottleneck effect and nonlinear effects at higher fluences. The results presented here are important to understand the nature of photo-generated charge carriers at the exciton energy level for developing advanced optoelectronic applications.