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Insights into the Femtosecond to Nanosecond Charge Carrier Kinetics in Perovskite Materials for Solar Cells

Pydzińska-Białek, Katarzyna, Szeremeta, Janusz, Wojciechowski, Konrad, Ziółek, Marcin
Journal of physical chemistry 2018 v.123 no.1 pp. 110-119
absorption, bleaching agents, fluorescence, iodides, lead, polymers, solar cells
In this work, we analyze a few simple methods that permit getting insight into the charge dynamics in methylammonium lead iodide (MAPbI₃) perovskites, on the basis of femtosecond transient absorption and fluorescence studies. We show that proper determination of the charge population decay kinetics requires broad spectral integration of the long-wavelength bleach signal (∼760 nm) assigned to the band-filling effect, which can be realized, e.g., by band integral analysis. On the contrary, the kinetics related to a shorter-wavelength bleach band (∼480 nm) behave differently: a single-wavelength decay is sufficient to probe charge population. Moreover, both the shorter-wavelength excitation and higher pump pulse intensities result in significantly longer charge cooling times, which might be important in efficient hot carrier extraction. The validity of our previously proposed easy approach for the elimination of higher-order recombination rates is also discussed and confirmed in terms of proper estimation of first-order decay rate constants. As an example, the rate constants of electron injection from MAPbI₃ to standard (6,6)-phenyl-C₆₁-butyric acid methyl ester (PCBM) material and the alternative PenPTC (also called PDI) and SPPO13 polymers are extracted and compared in inverted solar cells on the flexible substrate.