A low-cost, ligand exchange-free strategy to synthesize large-grained Cu₂ZnSnS₄ thin-films without a fine-grain underlayer from nanocrystals

Abstract

The first direct synthesis of CZTS nanocrystals in a formamide solvent system without using long hydrocarbon chain organic ligands is reported. The kesterite CZTS nanocrystals possess a mean size of 5.2 ± 1.2 nm. No secondary phases have been detected within the known limitations of XRD and Raman measurements. Experimental evidence suggests that excess S 2is present on the surface of the nanocrystals, accounting for their dispersibility in polar solvents. The nanocrystals also exhibit a smaller weight loss of 8.7% at 500°C compared to 24.4% for those capped by oleylamine. A description for the formation of CZTS FA nanocrystals and the role of formamide during synthesis is proposed. Annealing of spincoated nanocrystal thin-films highlighted the difficulty of forming dense films from loose nanocrystal films. This work shows that this can be overcome using compaction with a combination of reasonably soft metal and silicone. A means to compact the film uniformly on a centimeter scale with reduced delamination is thus demonstrated. Annealed compacted films possess crystal grains with a favorable size on the order of microns. More significantly, a large-grain layer is formed without an unwanted residual fine-grain underlayer. The absence of a fine-grain underlayer shows that this ligand exchange-free strategy is effective at resolving a key challenge associated with the nanocrystal approach of making CZTS thinfilms while simultaneously being low-cost and having a smaller environmental footprint. The strategy presented here is equally applicable to other nanocrystal approaches requiring the synthesis of dense thin-films from nanocrystal films.

Solution-Processed One-Dimensional ZnO@CdS Heterojunction toward Efficient Cu2ZnSnS4 Solar Cell with Inverted Structure

“…As shown in Fig. 3b, the Raman mode at around 326 cm −1 is associated with the as-prepared kesterite CZTS thin film, which was in consistent with the previous reports3839. Meanwhile, the mode intensity increased with the increased annealing temperature.…”

Influence of Ligands on the Formation of Kesterite Thin Films for Solar Cells: A Comparative Study

“…Point (2) is unlikely to be the reason for the difference as well. This is because the CZTS OLA nanocrystals were synthesized according to a recipe reported previously for which no copper sulfide phases existed in the Cu‐poor CZTS nanocrystals, and we did not detect copper sulfide phases in our CZTS OLA nanocrystals . Additionally, if we consider that the CZTS OLA nanocrystals were synthesized with a Cu‐poor composition and were more Cu poor than CZTS FA nanocrystals, it is less likely for copper sulfide to form during the synthesis of CZTS OLA nanocrystals.…”

Enhanced external quantum efficiency from Cu2ZnSn(S,Se)4 solar cells prepared from nanoparticle inks

“…10) However, the selenization of Cu 2 ZnSnS 4 (CZTS) nanoparticle inks currently provides the only approach that allows phase formation prior to the film deposition. 11,12) Recently, a CZTSSe solar cell (with an antireflective coating) fabricated from a CZTS nanoparticle ink has been reported with a solar energy conversion efficiency of 9.3%. 13) This progress was attributed to careful control of the nanoparticle synthesis.…”