Aqueous-Solution-Processed CuZnSn(S,Se) Thin-Film Solar Cells via an Improved Successive Ion-Layer-Adsorption-Reaction Sequence.

A facile improved successive ionic-layer adsorption and reaction (SILAR) sequence is described for the fabrication of CuZnSn(S,Se) (CZTSSe) thin-film solar cells (TFSCs) via the selenization of a precursor film. The precursor films were fabricated using a modified SILAR sequence to overcome compositional inhomogeneity due to different adsorptivities of the cations (Cu, Sn, and Zn) in a single cationic bath. Rapid thermal annealing of the precursor films under S and Se vapor atmospheres led to the formation of carbon-free CuZnSnS (CZTS) and CZTSSe absorber layers, respectively, with single large-grained layers. The best devices based on CZTS and CZTSSe absorber layers showed total area (∼0.30 cm) power conversion efficiencies (PCEs) of 1.96 and 3.74%, respectively, which are notably the first-demonstrated efficiencies using a modified SILAR sequence. Detailed diode analyses of these solar cells revealed that a high shunt conductance ( ), reverse saturation current density ( ), and ideality factor ( ) significantly affected the PCE, open-circuit voltage ( ), and fill factor (FF), whereas the short-circuit current density ( ) was dominated by the series resistance ( ) and . However, the diode analyses combined with the compositional and interface microstructural analyses shed light on further improvements to the device efficiency. The facile layer-by-layer growth of the kesterite CZTS-based thin films in aqueous solution provides a great promise as an environmentally benign pathway to fabricate a variety of multielement-component compounds with high compositional homogeneities.