Aqueous-Solution-Processed Cu2ZnSn(SSe)4 Thin-FilmSolar Cells via an Improved Successive Ion-Layer-Adsorption–ReactionSequence

摘要

A facile improved successive ionic-layer adsorption and reaction (SILAR) sequence is described for the fabrication of Cu2ZnSn(S,Se)4 (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⁺, Sn⁴⁺, and Zn²⁺) 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 Cu2ZnSnS4 (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 cm²) 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 (Gsh), reverse saturation current density (Jo), and ideality factor (nd) significantly affected the PCE, open-circuit voltage (Voc), and fill factor (FF), whereas the short-circuit current density (Jsc) was dominated by the series resistance (Rs) and Gsh. 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-layergrowth of the kesterite CZTS-based thin films in aqueous solutionprovides a great promise as an environmentally benign pathway to fabricatea variety of multielement-component compounds with high compositionalhomogeneities.