Determining exciton binding energy and reduced effective mass in metal tri-halide perovskites from optical and impedance spectroscopy measurements

This work presents a new method to accurately determine exciton binding energy and reduced effective mass in bulk halide perovskites by accounting for polarization effects from carrier-phonon interactions. The exciton-polaron binding energy is estimated using optical absorption measurements and the Elliott-based Band Fluctuations (EBF) model. The reduced effective mass is then derived by combining the results from the EBF model with the Pollmann-Buettner exciton-polaron theory, which incorporates electron-phonon coupling by leaving in consideration the ionic and electronic dielectric responses, as well as the LO phonon energy. When applied to $A\phantom{\rule{0}{0ex}}B\phantom{\rule{0}{0ex}}{X}_{3}$ perovskites ($A$ = MA, FA, Cs; $B$ = Pb; $X$ = I, Br, Cl), this approach shows excellent agreement with magnetoabsorption and other optical-resolved methods, confirming its accuracy and broad applicability which could be extended to other polar systems.