Recently, Cu2AgBiI6 semiconductor has been investigated due to the high absorption coefficient, direct bandgap, and low exciton binding energy, which are promising for eco-friendly photoelectric devices. Herein, pyridine is introduced as solvent additive to completely dissolve the solutes and form clear Cu2AgBiI6 precursor solution, which results in high-quality films and may provide a general approach for high-quality film growth of other bismuth-based metal halide semiconductors. In addition, the electronic structure of Cu2AgBiI6 has been demonstrated for the first time and shows an intrinsically weak n-type semiconductor. Furthermore, phenethylammonium iodide for surface passivation significantly improves the film quality, slightly n-dopes the material, and shifts up the band level. Finally, the photovoltaics and photodetector performance for n-i-p planar heterojunction devices have been investigated. The efficiency is up to 1%, highest for Cu2AgBiI6 solar cells and comparable with other lead-free bismuth based metal halide solar cells. Moreover, photodetectors with fast speed of rising and decaying time, especially the excellent specific photodetectivity of ∼1012 Jones within the wavelength of ∼350–600 nm, are achieved, which paves an alternative and promising strategy for the design of future commercial photodetectors that are self-powered, stable, nontoxic, etc.

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