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.
}}, author = {{Li, Yong and Yao, Zehan and Jiao, Chenxu and Wang, Zhengjun and Schlawin, Frank and Baranov, Dmitry}}, issn = {{2688-4062}}, keywords = {{carrier transfer; halide perovskites; low-temperature photophysics; methylammonium lead iodide (MAPbI); orthorhombic-tetragonal transition; phase coexistence; time-resolved photoluminescence; transient absorption spectroscopy}}, language = {{eng}}, number = {{6}}, publisher = {{Wiley}}, series = {{Small Structures}}, title = {{Ultrafast Carrier Dynamics in Methylammonium Lead Iodide (MAPbI3) Perovskite Thin Films With Coexisting Orthorhombic and Tetragonal Phases}}, url = {{http://dx.doi.org/10.1002/sstr.70515}}, doi = {{10.1002/sstr.70515}}, volume = {{7}}, year = {{2026}}, }