Cs3CuAs4Q8 (Q = S, Se): unique two-dimensional layered inorganic thioarsenates with the lowest Cu-to-As ratio and remarkable photocurrent responses.

Inorganic chalcogenides containing cations with lone-pair electrons have attracted considerable attention because of their potential applications in photocatalysis. In this research, two new copper thioarsenates with the lowest Cu-to-As ratio in the quaternary X/Cu/As/Q (X = inorganic cations; Q = chalcogen) system, namely Cs3CuAs4Q8 (Q = S, Se), were obtained by a simple surfactant-thermal method at a low temperature. These two isostructural compounds belong to the monoclinic space group C2/c (no. 15) and are composed charge-balanced Cs+ cations and two-dimensional anionic [CuAs4Q8]3- layers. Notably, photo-electrochemical measurements indicate that Cs3CuAs4Q8 possesses a remarkable photocurrent response under simulated solar-light illumination. Further theoretical studies were performed to gain insights into the relationships between electronic structure and optical properties.