Solvent-free synthesis of Cu₂ZnSnS₄ nanocrystals: a facile, green, up-scalable route for low cost photovoltaic cells

Abstract

Efficient Cu2ZnSnSe4 (CZTSe) solar cells were fabricated with a simple, environmentally friendly, and scalable synthetic method for Cu2ZnSnS4 (CZTS) nanocrystals. CZTS nanoparticles were mechanochemically synthesized from elemental precursors on a relatively large scale (∼20 g), during which no solvents or additives were used, thus alleviating the complex process of particle synthesis. An analysis of the time evolution of the crystalline phase and morphology of precursor powders revealed that the formation of the CZTS compound was completed in 0.5 h once initiated, suggesting that the mechanochemically induced self-propagating reaction prevails. CZTS ink was prepared by dispersing the as-synthesized nanoparticles in an environmentally benign solvent (160 mg mL(-1) in ethanol) without using any additives, after which it was cast onto Mo-coated glass substrates by a doctor-blade method. Subsequent reactive annealing at 560 °C under a Se-containing atmosphere resulted in substantial grain growth along with the nearly complete substitution of Se. The CZTSe solar cells therefrom exhibited power conversion efficiency levels as high as 6.1% (based on the active area, 0.44 cm(2)) with a relatively high open-circuit voltage (0.42 V) in comparison with the bandgap energy of 1.0 eV.

Influences of Extended Selenization on Cu2ZnSnSe4 Solar Cells Prepared from Quaternary Nanocrystal Ink

“…As shown in the figure, the phase transformation from CZTS nanocrystals (a few tens of nanometers in size) 17 Another concern over the prolonged annealing of CZTSe and its derivative materials is associated with the local phase decomposition. It has been reported that high-temperature annealing (> 500 °C) causes a loss of Sn, which is attributed to volatile components such as SnSe In a similar way, Sn loss during prolonged annealing would give rise to an accumulation of Zn in the surface region of the present film and hence overall changes in the metal ratio of the resulting of Zn in Figure S2 in the SI).…”

“…17 In order to produce device-quality CZTSSe absorbers with high crystallinity and a welldeveloped microstructure, a heat treatment of the precursor films at an elevated temperature (> 500 °C) is usually required. However, there are several concerns associated with an intensive heat treatment, which restricts the annealing temperature and duration time.…”

Chalcogenide Quaternary Cu2FeSnS4 Nanocrystals for Solar Cells: Explosive Character of Mechanochemical Synthesis and Environmental Challenge

“…We hypothesize that this is a result of the exothermic reaction taking place between Sn and CuS, as the latter should be definitely formed after this time of milling [33]. It has to be noted that the rapid consumption of tin was also documented in the synthesis of CZTS nanocrystals, despite the fact that the reaction proceeded more-or-less in a gradual manner until that point [24]. The maximum pressure (1513 mbar) was evidenced after 25 min of milling.…”

“…The combination of mechanical alloying and spark plasma sintering has documented the possibility to synthesize high-performance thermoelectric materials with the possibility to scale the synthesis process. While CZTS has been already synthesized by a mechanochemical route in 2011 [21] and plenty of papers on this topic have emerged [22][23][24][25][26][27][28][29], literature on Cu 2 FeSn 3 S 8 (CFTS) mechanochemical synthesis is rather scarce. In 2014, an attempt was published to apply mechanochemistry for the synthesis of CFTS [23].…”

Photovoltaic materials: Cu2ZnSnS4 (CZTS) nanocrystals synthesized via industrially scalable, green, one‐step mechanochemical process

“…Various precursors were applied-either elements or compounds. As for milling, dry mode 12,13,15,[18][19][20][21][22][23][24][25][26] and wet mode 14,16,17,27 were applied. However, the wet mode was not primarily used for synthesis but rather to improve the homogeneity of already-prepared CZTS applied for subsequent thin film formation.…”