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The electrochemical deposition of Ga and Cu-Ga alloys from the deep eutectic solvent choline chloride/urea (Reline) is investigated to prepare CuGaSe(2) (CGS) semiconductors for their use in thin film solar cells. Ga electrodeposition is difficult from aqueous solution due to its low standard potential and the interfering hydrogen evolution reaction (HER). Ionic liquid electrolytes offer a better thermal stability and larger potential window and thus eliminate the interference of solvent breakdown reactions during Ga deposition. We demonstrate that metallic Ga can be electrodeposited from Reline without HER interference with high plating efficiency on Mo and Cu electrodes. A new low cost synthetic route for the preparation of CuGaSe(2) absorber thin films is presented and involves the one-step electrodeposition of Cu-Ga precursors from Reline followed by thermal annealing. Rotating disk electrode (RDE) cyclic voltammetry (CV) is used in combination with viscosity measurements to determine the diffusion coefficients of gallium and copper ions in Reline. The composition of the codeposited Cu-Ga precursor layers can be controlled to form Cu/Ga thin films with precise stoichiometry, which is important for achieving good optoelectronic properties of the final CuGaSe(2) absorbers. The morphology, the chemical composition and the crystal structure of the deposited thin films are analysed by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffraction (XRD). Annealing of the Cu-Ga films in a selenium atmosphere allowed the formation of high quality CuGaSe(2) absorber layers. Completed CGS solar cells achieved a 4.1% total area power conversion efficiency.

Thin film solar cells based on nontoxic and earth-abundant elements are necessary for future-generation photovoltaic devices. Tin monosulfide is a promising candidate that can be used as an absorber material in thin film photovoltaics. In this paper, we introduce the direct synthesis of stoichiometric and single-phase p-type SnS films via the electrodeposition from the ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([C4mim][DCA]) containing elemental sulfur and SnCl2 at high temperature. The electrochemical behavior is studied, and a deposition mechanism of tin monosulfide from the elemental sulfur saturated ionic liquid is proposed. XRD, XPS, and Raman spectroscopy demonstrate the sole presence of α-SnS without any secondary sulfide phases (e.g., SnS2, Sn2S3). XPS depth profiling confirmed the phase purity and disproved the presence of organic contamination in the as-deposited films. Photoelectrochemical measurements affirmed the p-type conductivity of the SnS films. The as-deposited layers have an indirect optical band gap at 1.17 eV and high optical absorption (α ≥ 104 cm–1) at photon energy above 1.4 eV. First solar cells with a standard thin film substrate cell configuration are presented.

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