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

Abstract

Highly photoluminescent, lead‐free perovskites are of interest for displays and solid‐state light‐emitting devices. In this report, streak camera‐based time‐resolved emission and transient absorption spanning visible to deep‐ultraviolet (UV) wavelengths are utilized to study self‐trapped and free exciton dynamics in vacuum‐deposited cesium copper halide thin films of CsCu2I3 and Cs3Cu2I5. Self‐trapped exciton emission of CsCu2I3 exhibits more noticeable changes with time in the peak position and width than Cs3Cu2I5. UV‐to‐blue emission is detectable for both compositions, where free exciton emission is distinct for CsCu2I3. Transient absorption shows 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 time constants in these materials that build an overall dynamic scheme. This work aids in building a complete picture regarding light emission in these promising materials.

Nature of Self-Trapped Exciton Emission in Zero-Dimensional Cs2ZrCl6 Perovskite Nanocrystals

“…The microsecond time scale dynamics of STEs in Cs 2 ZrCl 6 NCs can be observed from the time-resolved PL based on time-correlated single-photon counting (TCSPC) measurements (Figure d), which agrees well with earlier studies. , So far, little is known about the formation of STEs and their relaxation processes at subpicosecond to picosecond time scales in Cs 2 ZrCl 6 NCs. ,, In our analysis, we employed the streak camera technique, which offers a time resolution of tens of picoseconds, to examine the radiative recombination process of STEs. This method is complementary to the TCSPC technique.…”

“…Numerous efforts have been devoted to developing novel low dimensional perovskite-inspired materials with efficient STE emissions. However, the more fundamental studies addressing the photophysics and dynamics of STEs in low dimensional perovskite-inspired materials are still rare. , A thorough understanding of the formation and relaxation processes of STEs is significant to further improve their performance and develop new low dimensional perovskite-inspired materials for advanced optoelectronic applications. The recently reported 0D vacancy-ordered double perovskite Cs 2 ZrCl 6 showed typical STE emission with high efficiency and outstanding chemical stability, ensuring its potentiality in versatile applications including LEDs and X-ray scintillator screens. , Herein, we explored the photoinduced exciton dynamics of these Cs 2 ZrCl 6 nanocrystals (NCs) by utilizing ultrafast time-resolved optical spectroscopies, which can obtain a deep understanding of the STEs in both Cs 2 ZrCl 6 and its perovskite counterparts.…”

Uniform nucleation and growth of Cs3Cu2I5nanocrystals with high luminous efficiency and structural stability and their application in white light-emitting diodes

“…[38][39][40] Such a large Stokes shift and the broad-band feature imply that the emission may be caused by the radiative recombination of self-trapped excitons (STEs). [41][42][43] Since the PL spectrum can be deconvoluted into two peaks at 418 nm ( peak a) and 455 nm ( peak b) (Fig. S4 †), this may imply two STEs with different depths.…”

Bright lead-free Cs3Cu2I5 perovskite scintillators for thermal neutron detection

“…The peak position at 3.84 eV is assigned to tiny impurities of CsCuI 3 in the products, which are reported by Chen et al . 50 The peak positions at 4.26 eV and 4.54 eV result from the excitonic absorption peak and band edge absorption peak, respectively. 51 Usually, the band edge absorption peak cannot be identified in PLE spectra.…”