Crystalline structures and optoelectronic properties of orthorhombic CsPbBr3 polycrystalline films grown by the Co-evaporation method

In order to fabricate pure-phase CsPbBr3 films with high crystalline quality, the stoichiometry between precursors is of great importance. However, the precise control of the stoichiometry is difficult for solution processed methods, which is hindered by the poor solubility of CsBr in commonly used solvents. On the other hand, in terms of co-evaporation method, the stoichiometry of CsPbBr3 films can be easily modulated by controlling the deposition rates of precursors. Herein, the impact of deposition rate ratio between CsBr and PbBr2 on the crystalline quality and optoelectronic properties of orthorhombic CsPbBr3 polycrystalline films has been investigated. CsPbBr3 polycrystalline films with high crystalline quality and preferential crystalline orientation have been fabricated using co-evaporation method at the optimized deposition rate ratio. The reversible structural transformation from orthorhombic to cubic phase CsPbBr3 films is confirmed using temperature-dependent XRD characterizations. At the deposition ratio of 0.5:0.7, largest grain size of 7.82 × 104 nm2 along with a high uniformity is observed for CsPbBr3 films. Moreover, the longest lifetime of 24.0 ns for photo-generated exciton within CsPbBr3 films has also been revealed at the optimized deposition rate ratio. Because of the high crystalline quality and prolonged lifetime for photo-generated exciton, a photoresponsivity of 20.2 A/W and external quantum efficiency of 48.7% are achieved for CsPbBr3 based photodetector. Our findings demonstrate a facile approach for the growth of CsPbBr3 polycrystalline films with high crystalline quality and promote their applications in optoelectronic devices.