The synthesis and photovoltaic effect of Cu3xBi1−xI3 (CBI) thin films were studied. Although CBI was originally inspired by the material class of Caswellsilverites (also known as Rudorffites), an XRD study showed that its crystal structure resembles a BiI3-cage with interstitial copper. CBI was found to demonstrate optoelectronic properties suitable for solar light harvesting, including a band gap of 1.66 eV and thermal stability up to 333 °C. The corresponding thin film solar cells achieved a peak power conversion efficiency of 0.65%.
