Optical studies on high-quality thin films and single crystals are required for a deep understanding of the intrinsic optoelectronic properties of lead-halide perovskites. We studied photocarrier dynamics of high-quality CH3NH3PbI3 and CH3NH3PbBr3thin films and single crystals using one-photon excited PL (1PL) and two-photon excited PL (2PL) spectroscopy [5-7]. In thick single crystals, the photocarriers are generated at the near-surface region under one-photon excitation and in the interior region under two-photon excitation. The time-integrated 1PL peak energy is higher than the 2PL peak energy. The 1PL peak energy shifts to lower energy with delay time after laser excitation. The 1PL lifetime is shorter than the 2PL lifetime. These dynamical PL behaviors of thick single crystals are different from those of thin films. In thin films, the photocarriers are created homogeneously throughout the sample thickness under one- and two-photon excitation . The spatial distribution of photocarriers determines the PL spectrum and dynamics: The PL dynamics of thick single crystals can be explained by fast carrier diffusion and photon recycling (photon emission and reabsorption) [5-7].
In SC device structures, the perovskite CH3NH3PbI3 layer is sandwiched between the mesoporous TiO2electron-transport layer and the spiro-OMeTAD hole-transport layer. Charge carrier dynamics in the perovskite solar cells were studied by means of PL and photocurrent (PC) imaging spectroscopy. Simultaneous PL and PC imaging measurements revealed a positive correlation between the PL intensity and PL lifetime, and a negative correlation between PL and PC intensities . These correlations are a result of the competition between the escape of photocarriers from the perovskite layer and the recombination of photocarriers within the perovskite layer. Moreover, from the excitation-fluence dependence of the PL decay curves in thin films and SCs, we conclude that the carrier injection at the interface determines the device performance of perovskite SC [9,10]. Our systematic PL studies provide an essential information for developing high-performance devices based on metal-halide perovskites.
Part of this work was supported by JST-CREST (Grant No. JPMJCR16N3).
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