AIn4S6Cl (A = Rb and Cs) and Pb5Sn3Q10Cl2 (Q = S and Se): quaternary chalcohalides with mixed anionic coordination exhibit photocurrent responses

Abstract

Mixed-anionic compounds have caught considerable attention due to their flexible coordination manners and abundant physical properties. Four new chalcohalides RbIn₄S₆Cl (1), CsIn₄S₆Cl (2), Pb₅Sn₃S₁₀Cl₂ (3) and Pb₅Sn₃Se₁₀Cl₂ (4) were successfully obtained by the high-temperature halide salt flux method. Compounds 1 and 2 have layered structures that consist of octahedral InS₆ and aliovalent-anionic InS₃Cl units. Compounds 3 and 4 feature 3-D structural frameworks built by [Pb₄SnQ₈Cl₄]⁶⁻ and [PbSn₂Q₆]²⁻ (Q = S and Se) polyhedral chains, in which partial Pb²⁺ cations are coordinated by Q²⁻ and Cl⁻ anions. Compounds 1–4 have optical band gaps close to the wavelength range of visible light and exhibit significant photocurrent responses of 28.75 nA cm⁻², 55.12 nA cm⁻², 19.58 mA cm⁻², and 36.12 μA cm⁻² with on/off ratios 30.0, 2.5, 15.7 and 2.6, respectively, implying their potential for photovoltaic applications. To the best of our knowledge, compound 3 has the largest photocurrent response among all non-oxides. In addition, the activation energies of 1–4 are well below 0.3 eV, which makes these compounds interesting for potential applications in electrochemical devices. This work sheds light on the exploration of promising photocurrent response materials in the mixed-anionic compound system.