A monoclinic crystal structure and a reusable stress-controlled optoelectronic switch in a lead halide perovskite, CsPbBr3

Abstract

Lead halide perovskites are prominent materials for many industrial applications, including energy conversion. They are relatively soft, and their optoelectronic properties are sensitive to applied mechanical stresses. Herein, we experimentally demonstrate that CsPbBr₃ can potentially be used as a stress-controlled element, whose optoelectronic characteristics can be switched by applying a stress value above 1 GPa. We synthesized single crystals of CsPbBr₃, determined its crystal structure, and accurately measured its electrical resistance as a function of applied pressure for eight cycles of compression to 12 GPa. Above 1 GPa, we observed an abrupt three-order jump in resistance and attributed it to a phase transition to a disordered phase, accompanied by band gap widening. We found this phase transition to be well reproducible under multiple cycling, without notable shift in the transition pressure and widening of the transition region with the cycle number. This result was in sharp contrast to expectations. We proposed that this behaviour can be related to a highly unusual nature of the transition in which the abrupt widening and narrowing of the band gap are controlled by a cyclical migration of some bromine atoms from their crystallographic sites into interstices (i.e., the formation of Frenkel defects) and back (i.e., their ‘self-healing’), under the action of applied stress. Comparative photoluminescence spectroscopy of the original crystal and the one recovered after the high-pressure experiments found that in the latter the band gap increases slightly. Our results suggest that CsPbBr₃ could be utilized in optoelectronic devices employing stress-controlled elements.