2015 Volume 70 Issue 12 Pages 926-931
Lead-halide perovskite semiconductors CH_3NH_3PbX_3 (X=Cl, Br, and I) have currently come into the limelight because of their promising features for solar cell applications. The maximum efficiency of perovskite-based solar cells has already reached above 20%. Studies on three-dimensional halide perovskite CH_3NH_3PbX_3 started from the early 1970s, however, their optical and electrical properties have not been clarified compared with the associated two- and one-dimensional perovskites. We studied the optical properties and photocarrier recombination dynamics in CH_3NH_3PbI_3 using time-resolved laser spectroscopy and revealed that electron-hole radiative recombination dominates the photocarrier dynamics at room temperature. Our findings demonstrate that the photoexcited electrons and holes behave as free carriers in CH_3NH_3PbI_3, because of its small exciton binding energy. This feature is closely related to the high energy-conversion efficiencies of perovskite solar cells. We discuss future perspectives on perovskite semiconductor physics and perovskite solar cells.