Ultrafast Excited-State Transport and Decay Dynamics in Cesium Lead Mixed Halide Perovskites

Abstract

While significant research efforts directed toward characterizing the excited-state dynamics of lead halide perovskites have enabled promising advances in photovoltaic, light-emitting diode, and laser technologies, a detailed correlation between composition and functionality in this promising class of materials remains unestablished. We use pump−probe microscopy to characterize both transport and relaxation dynamics in individual crystals of CsPbI 2 Br, a mixed halide, all-inorganic analogue to the well-studied organic−inorganic hybrid perovskites. In contrast to the methylammonium lead tri-iodide perovskite, we find excited-state dynamics that decay primarily via first-order and Auger mechanisms. By global fitting of power-dependent kinetics collected from individual domains, we find a range of Auger rate constants between 3.3 × 10 −30 and 1.5 × 10 −28 cm 6 /s, with negligible contributions from secondorder (bimolecular) processes. Direct imaging of the excited-state spatial evolution reveals an average diffusion constant of 0.27 cm 2 /s, a value that is nearly an order of magnitude smaller than that of single-crystal, organic−inorganic analogues.

Inorganic CsPbI2Br Perovskite Solar Cells: The Progress and Perspective

“…The exciton binding energy (22 ± 3 meV) and reduced mass (0.124 ± 0.02 m 0 ) have been extracted from analyzing of the full magnetic field dependence on both hydrogenic and free carrier transitions. The exciton binding energy of CsPbI 2 Br is slightly larger than that of MAPbI 3 (16 meV) and CsPbI 3 (15 ± 1 meV) perovskites, but the excitons in CsPbI 2 Br perovskites can still dissociate into free carriers at room temperature. The effective dielectric constant ϵ eff of 8.6 has also been determined from the exciton binding energy and reduced effective mass.…”

“…The value is significantly lower than the mobility of MAPbI 3 (28–68 cm 2 Vs −1 ) . The reducing in mobility of CsPbI 2 Br in comparison with hybrid MAPbI 3 perovskites is dominant by the higher trap density . Therefore, passivation of the trap states is essentially vital to enhance the charge carrier mobilities of CsPbI 2 Br films and thus to obtain PSCs with higher‐performances.…”

“…e) Histogram of diffusion constants measured for 12 individual domains. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…Therefore, passivation of the trap states is essentially vital to enhance the charge carrier mobilities of CsPbI 2 Br films and thus to obtain PSCs with higher‐performances. Note that the orthorhombic CsPbI 2 Br perovskite was used in this work, whose semiconductor properties are poorer than that of cubic CsPbI 2 Br, which has been typically used in PSCs. The effect of crystal phase on charge carrier transport and recombination properties is still waiting for deeply exploring.…”

Anorganische CsPbX3‐Perowskit‐Solarzellen: Fortschritte und Perspektiven

“…B. den III-V-Halbleitern), über den gesamten sichtbaren und Nah-IR-Bereich abgestimmt werden. 10 cm 2 V À1 s À1 )f ürC sPbI 2 Br [51] und grçßere Werte (38 cm 2 V À1 s À1 )f ürC sPbBr 3 [52] gefunden. Es scheint, dass die Mobilitätswerte fürC sPb-HaPs denen der entsprechenden Hybrid-HaPs ähnlich sind.…”