Self-Trapped and Free Exciton Dynamics in Vacuum-Deposited Cesium Copper Iodide Thin Films

摘要

Highly photoluminescent, lead-free perovskites are of interest for displaysand solid-state light-emitting devices. In this report, streak camera-basedtime-resolved emission and transient absorption spanning visible todeep-ultraviolet (UV) wavelengths are utilized to study self-trapped andfree exciton dynamics in vacuum-deposited cesium copper halide thinfilms of CsCu_2I_3 and Cs_3Cu_2I_5. Self-trapped exciton emission of CsCu_2I_3exhibits more noticeable changes with time in the peak position and widththan Cs_3Cu_2I_5. UV-to-blue emission is detectable for both compositions,where free exciton emission is distinct for CsCu_2I_3. Transient absorptionshows loss of ground-state bleach signals at early time delays for both,and the bleach signal shifts toward higher energy as time delay increases,likely due to strains induced by the newly created self-trapped excitons.Global analysis performed on the transient absorption results yields timeconstants in these materials that build an overall dynamic scheme. Thiswork aids in building a complete picture regarding light emission in thesepromising materials.