Development and Properties of Surfactant‐Free Water‐Dispersible Cu₂ZnSnS₄ Nanocrystals: A Material for Low‐Cost Photovoltaics

Abstract

A simple, yet novel hydrothermal method has been developed to synthesize surfactant-free Cu2ZnSnS4 nanocrystal ink in water. The environmentally friendly, 2-4 nm ultrafine particles are stable in water for several weeks. Detailed X-ray diffraction (XRD) and high-resolution transmission electron microscopy revealed the formation of single-crystalline-kesterite-phase Cu2ZnSnS4. Elemental mapping by scanning electron microscopy/energy dispersive spectrometry corroborated the presence of all four elements in a stoichiometric ratio with minor sulfur deficiency. Finally, Raman spectroscopy ruled out the possible presence of impurities of ZnS, Cu2SnS3, SnS, SnS2, Cu(2-x)S, or Sn2S3, which often interfere with the XRD and optical spectra of Cu2ZnSnS4. X-ray photoelectron spectroscopic studies of the as-synthesized samples confirmed that the oxidation states of the four elements match those of the bulk sample. Optical absorption analyses of thin film and solution samples showed high absorption efficiency (>10(4) cm(-1)) across the visible and near-infrared spectral regions and a band gap E(g) of 1.75 eV for the as-synthesized sample. A non-ohmic asymmetric rectifying response was observed in the I-V measurement at room temperature. The nonlinearity was more pronounced for this p-type semiconductor when the resistance was measured against temperature in the range 180-400 K, which was detected in the hot-point probe measurement.

A nontoxic and low-cost hydrothermal route for synthesis of hierarchical Cu2ZnSnS4 particles

“…Undoubtedly, if water is used to replace these organic solvents, a hydrothermal route will be developed, which is more desirable for the environment-friendly and low-cost synthesis of CZTS nanocrystalline materials. However, few investigations on synthesis of CZTS nanocrystalline materials by the hydrothermal method have been reported, except the hydrothermal reactions with Na 2 S [31] or thiourea [32] as the sulfur source. Note that selecting a suitable sulfur source is important for exploring a green hydrothermal process for preparing CZTS nanocrystalline materials.…”

Multifunctional Copper‐Based Quaternary Chalcogenide Semiconductors Toward State‐of‐the‐Art Energy Applications

“…Similarly, Δ H f (CZTX)−Δ H f (Cu 2 X)−Δ H f (ZnX)−Δ H f (SnX 2 )<0 and Δ H f (CZTX)−Δ H f 2(CuX)−Δ H f (ZnX)−Δ H f (SnX)<0 for the formation of pure CZTX phase. The quaternary compound can also be synthesized by mixing the binary compounds Cu 2 X+ZnX+SnX 2 and 2CuX+ZnX+SnX stoichiometrically under high temperature conditions as has been demonstrated in various synthesis procedures ,,,,. The schematic representation of the CZTS phase diagram is shown in Figure , which depicts the potential stability region for stable CZTS formation and conditions necessary to avoid the formation of other binary and ternary phases.…”

“…The large scale and low cost synthesis of NPs could be done through hydro/solvothermal methods ,. Chemical reaction occurs in a sealed autoclave filled with precursor solution at controlled temperature (typically <300 °C) and indigenous pressure, which leads to the formation of product.…”

“…The search for cheap and effective material for PV application led to the emergence of Cu‐based quaternary chalcogenides Cu 2 ZnSnX 4 (CZTX; X=S, Se) as potential alternative materials in place of expensive Si‐based PV technology ,,,. The Cu 2 ZnSnX 4 materials constitute of cheap as well as geologically abundant elements .…”

“…The comparison of the materials with Si in terms of material extraction cost and power production capacity shows the great potential of the former to be established as efficient PV material ,,. The scaled‐up synthesis procedures and versatile techniques have been established to further reduce the cost function for its effective commercial PV realization ,,. Interestingly, huge range of Cu‐based quaternary chalcogenide Cu 2 M I M II X 4 (where, M I =Zn, Ni, Co, Fe, Mn, Cd and Hg; M II =Si, Sn and Ge and X=S and/or Se) materials have been emerged in the recent time claiming vivid application of these material in diverse fields ,,,.…”