Dmitry Baranov

Methylammonium lead iodide (MAPbI₃) is a prototypical soft-lattice semiconductor whose orthorhombic and tetragonal polymorphs can coexist and interconvert under optical excitation or changes in temperature. The mixed-phase regime attracts attention because of the carrier transfer between phases, which enables optoelectronic functionalities such as optical gain. Here, we investigate carrier dynamics in mixed-phase MAPbI₃ thin films by comparing laser-induced phase coexistence at 77 K using time-resolved photoluminescence with thermally-induced phase coexistence at 148 K using transient absorption (TA) spectroscopy. By using low-repetition-rate TA to mitigate cumulative heating and avoid thermally induced phase conversion, we resolve the distinct spectral fingerprints of the orthorhombic and tetragonal phases and identify two carrier-transfer timescales of 36 and 539 ps, attributed to interfacial and bulk-mediated transfer, respectively. Despite carrier funneling in the mixed phase and high carrier densities, these conditions do not inherently lead to observable optical gain in the studied films.