Unveiling the effect of hypophosphorous acid for the growth of high quality Cs3Cu2I5 single crystals

The zero-dimensional copper halide perovskite Cs3Cu2I5 displays extraordinary luminescence and scintillation characteristics, and high-quality crystals are extremely desirable for exploring the commercial applications. Currently, the most critical issue in the solution growth of Cs3Cu2I5 crystals is the easy oxidation of halides, which significantly hinders the optimization of crystal qualities. The hypophosphorous acid (H3PO2) has been applied to inhibit the oxidation, nevertheless, the related mechanism is elusive and has been largely ignored. Herein, Cs3Cu2I5 crystals have been grown from N, N-Dimethylformamide (DMF) solvent by the antisolvent vapor-assisted crystallization (AVC) method. It is verified that H3PO2 effectively prevents the oxidation of Cs3Cu2I5 by rapidly reducing Cu2+ and I3-, maintaining the stability of the precursor solution and continuously suppressing oxidation during the whole growth process. Meanwhile, by increasing the acidity of the solution, H3PO2 dissolve precursor colloids and efficiently enhance the solubility of halides. Thus, the addition of H3PO2 favors the rapid growth of centimeter-sized Cs3Cu2I5 crystals with well-defined crystallographic planes within several days. As excellent gamma ray scintillator, the crystal exhibits high light yield of 38000 photons/MeV, with energy resolution of 5.6% at 662 keV. This work deeply elucidates new insight into the critical effect of H3PO2 in the DMF based solution crystal growth, facilitating the preparation of large-size and high-performance copper halide perovskite crystals.