Unraveling the Phase Transition and Luminescence Tuning of Pb-Free Cs–Cu–I Perovskites Enabled by Reaction Temperature and Polar Solvent

Abstract

Ternary Pb-free Cs−Cu−I perovskites have attracted widespread attention because of their excellent optical properties and environmentally friendly advantages. Herein, two different Pb-free ternary Cs 3 Cu 2 I 5 nanocrystals (NCs) and CsCu 2 I 3 microrods (MRs) were synthesized via a heating method. The phase and morphology transition from blue emission of Cs 3 Cu 2 I 5 NCs to yellow emission of CsCu 2 I 3 MRs could be tuned effectively by manipulating the reaction temperature, decreasing the maximum photoluminescence quantum yields (PLQYs) from 82.7% to ∼10%. More interestingly, the Cs 3 Cu 2 I 5 NCs could self-assemble into stacking chains, which exhibited a strong dependence on the polarity of solvents. In addition, it was demonstrated that the rapid phase transition and luminescence tuning between Cs 3 Cu 2 I 5 and CsCu 2 I 3 films took only a few seconds by direct heating or exposure to the polar solvent. This work may deepen the understanding of the phase transition process in Cu-based perovskites and provide a fluorescence material with a short switching time for anticounterfeiting applications.

Phase transition and rapid temperature response of lead-free perovskite Cs–Cu–I nanocrystals enabled by their size

“…The formula is as follows: Cs 3 Cu 2 I 5 –2CsI = CsCu 2 I 3 . 31 Therefore, the small sized Cs 3 Cu 2 I 5 NCs have faster phase transition when heated and show quicker temperature response.…”

“…This response time is shorter than the thermochromic perovskites reported previously (Table S1, ESI †). 31,40,41 PL spectra were obtained on the test paper before and after heating. Before heating, there was only an emitting peak at 450 nm, and after heating, there was an emitting peak at 575 nm, which further indicated that the transition from blue-phase Cs 3 Cu 2 I 5 to yellow-phase CsCu 2 I 3 occurred after high-temperature heating.…”

“…The hot-injection method has the advantages of short reaction times and a low preparation costs. 31 More importantly, NCs with different structures and morphologies can be synthesized by changing the reaction conditions, and these NCs have uniform size and excellent dispersion. 32,33 In this work, a feasible hot-injection method was adopted to synthesize blue-emitting (450 nm) Cs 3 Cu 2 I 5 NCs with controllable size.…”

Temperature-Induced Reversible Fluorescence Discoloration of Cs3Cu2Br5 and Its Application in X-ray Imaging

“…The PL intensity of orange emission gradually decreases with increasing temperature, while that of blue emission first increases and then decreases, reaching a peak at 260 K. The significant difference in PL spectra of Cs 3 Cu 2 Br 5 at 80 and 300 K indicates the presence of two different luminescent transitions in the system. According to the literature, this phenomenon may be related to phase transitions of copper-based halides, which alter their radiative transition energies . XRD measurements are performed on the samples at different temperatures to verify whether the phase transition occurs at low temperatures.…”

“…According to the literature, this phenomenon may be related to phase transitions of copper-based halides, which alter their radiative transition energies. 35 XRD measurements are performed on the samples at different temperatures to verify whether the phase transition occurs at low temperatures. Figure 3c shows that the peak positions of the sample and the XRD card are not as accurately matched as those before, which may be attributed to zero drift.…”