Impact of Trap Depth on the Steady-State and Transient Photoluminescence in Halide Perovskite Films

Within the field of halide perovskites, trap-assisted recombination is often considered to be synonymous with first-order recombination, that is, recombination that scales linearly with the charge-carrier concentration. However, the standard Shockley-Read-Hall statistics naturally predict that trap-assisted recombination can have any scaling between linear and quadratic with carrier density, depending on the position of the trap or defect that enables recombination. In an intrinsic semiconductor, the shallower a trap is, the more the recombination rate will scale quadratically with carrier density, and the more it will resemble radiative recombination in its behavior in any transient experiment. Here, the theoretical implications of the trap depth in general and shallow traps in particular on transient and steady-state experiments applied to halide perovskite samples for photovoltaic or optoelectronic applications are discussed.