A Hot-Injection, Low-Temperature Colloidal Route to Phase-Pure CuBiSCl2 Chalcohalide Submicron Crystals for Solution-Processed Thin Films

Lead-free chalcohalides are promising semiconductors, combining chalcogenide stability with mixed-anion versatility and low toxicity. Among them, CuBiSCl2 is attractive due to its quasi-direct band gap and strong near-infrared absorption. However, its synthesis has been limited to high-temperature solid-state methods, hindering thin film processing. Here, we report the first low-temperature (150 °C) colloidal hot-injection synthesis of phase-pure CuBiSCl2 submicron crystals with a platelet-like morphology and demonstrate their integration into solution-processed thin films and planar photoconductive devices. Spin-coated films are compact and uniform, exhibiting a band gap of ∼1.49 eV. The materials are stable under controlled conditions but undergo irreversible phase evolution upon exposure to air and heating. A proof-of-concept device made with CuBiSCl2 exhibits a photoresponse under 590 nm illumination, with a spectral responsivity of 5 × 10–6 A/W under an applied bias of 2 V and a photocurrent of ∼100 nA. This result establishes CuBiSCl2 as a promising material for optoelectronic and photovoltaic applications.