| 研究実績の概要 |
The CH3NH3PbI3 (MAPbI3) perovskite have been utilized mostly for single-junction perovskite solar cells because of its suitable bandgap for sunlight absorption. For the tandem solar cell application, the MAPbBr3 and mixed-halide (MAPb(I1-xBrx)3 perovskites can be used as a top cell material. We studied the optical properties of MAPbBr3 and mixed-halide (MAPb(I1-xBrx)3 for the perovskites using various spectroscopic optical techniques. We clarified the photocarrier recombination dynamics in I-rich mixed-halide MAPb(I1-xBrx)3 (x = 0 - 0.35) perovskite thin films using nanosecond time-resolved PL and picosecond transient absorption (TA) spectroscopy. Based on the time-resolved PL data, we found that increasing the Br content leads to a slight enhancement in the single-carrier trapping rate, which we attributed to be an increase in the alloy disorder in the Br-containing thin films. Moreover, by performing a global fitting of the TA decay dynamics obtained under various excitation fluences, we were also able to determine the Br-composition dependence of the two-carrier radiative and three-carrier Auger recombination rates. The significant increases in the nonlinear recombination rates with higher Br compositions, up to one order of magnitude, appeared. This is connected to the enhancement in Coulomb interactions between electrons and holes originated from changes in the electronic structure, including the dielectric constant and the effective mass upon the Br incorporation. We also determined the exciton binding energy of MAPbBr3 single crystals.
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