Non-toxic Cu₃BiS₃ thin film solar cells with Al doped TiO₂ as electron-transport layers

Abstract Cu 3 BiS 3 has been considered as an attractive photovoltaic material due to its suitable bandgap, excellent photoelectric properties, abundant component elements and low toxicity. However, most of the reported Cu 3 BiS 3 solar cells contain toxic components in other functioning layers such as CdS in electron-transport layers (ETLs). In this study, the Cu 3 BiS 3 thin films were prepared by spin-coating method. We find that the CuCl concentration in precursor solutions has influences on both the optical bandgap and grain size of the Cu 3 BiS 3 thin films, thus affecting the performance of solar cells. The optimal CuCl concentration is 0.91 M. Besides, Al doped TiO 2 (ATO) and MoO x films are employed as ETLs and hole-transport layers (HTLs) respectively, constructing a totally non-toxic thin film solar cell. Moreover, it is demonstrated that the ratio ( R Al:Ti ) of Al source (Aluminum nitrate nonahydrate) to Ti source [Titanium diisopropoxide bis(acetylacetonate)] in the precursor solution of ATO and the thickness of MoO x have significant influences on solar cells. Moderate Al doping in ATO, e.g. R Al:Ti =1:50, can produce oxygen vacancies and accelerate the interfacial charge transfer, thus resulting in the increased short-circuit current density and fill factor. With the optimized Cu 3 BiS 3 absorber, ETL and HTL, improved cell performances are observed comparted to the spin-coated Cu 3 BiS 3 counterparts with CdS as ETLs in literature.