Divergent Ultrafast Carrier-Density and Photoconductivity Dynamics in Antimony-Doped Halide Perovskite Thin Films

Heterovalent ion substitution can tune the optoelectronic properties of metal halide perovskites, but its impact on charge-carrier recombination and transport remain poorly understood. Here, we investigate antimony incorporation in methylammonium lead iodide (MAPI) thin films using complementary ultrafast spectroscopy techniques. Optical absorption shows that the bandgap remains approximately 1.61 eV across substitution levels up to 10%, whereas photoluminescence and transient absorption (TA) spectroscopy reveal increasing nonradiative recombination rates with increasing antimony content. Optical pump–terahertz probe (OPTP) spectroscopy further uncovers fluence-dependent dynamics distinct from TA that are absent in pristine MAPI. After considering alternative mechanisms, we interpret this behavior as consistent with partially heterogeneous transport, in which Sb3+ incorporation may introduce low-mobility, defect-rich regions within a higher-mobility crystalline network. Thus, heterovalent substitution can introduce hidden transport losses without changing optical bandgap, highlighting the importance of mobility-sensitive measurements to probe doped perovskite films.