Synthesis and Post-Annealing of Cu2ZnSnS4 Absorber Layers Based on Oleylamine/1-dodecanethiol

Abstract

Cu2ZnSnS4 (CZTS) nanocrystals in oleylamine (OLA) and 1-dodecanethiol (1-DDT) solvents were successfully prepared via hot-injection method, to produce inks for the deposition of absorber layers in photovoltaic cells. In this process, 1-DDT acts as a coordinating ligand to control the nucleation and growth of CZTS nanocrystals, whereas lower amounts of OLA promote a homogeneous growth of the grains in the absorber layer. X-Ray Diffraction (XRD) revealed both tetragonal and hexagonal phases of CTZS in films obtained after soft thermal treatments (labeled TT0). In particular, 1-DDT is responsible for the formation of a greater percentage of the hexagonal phase (ZnS-wurtzite type) than that formed when only OLA is used. The thermal treatments have been varied from 500 °C to 600 °C for improving crystallization and eliminating secondary phases. Both features are known to promote CZTS thin films with band gap values typical of CZTS (1.5–1.6 eV) and suitable resistivity. This study let to compare also the CZTS post-annealing without (TT1) and with sulfur vapor (TT2) in a tubular furnace. Only tetragonal CZTS phase is observed in the XRD pattern of CZTS thin films after TT2. A small presence of localized residues of secondary phases on the same samples was revealed by μRaman measurements. The best values of band gap (1.50 eV) and resistivity (1.05 ohm.cm) were obtained after thermal treatment at 500 °C, which is suitable for absorber layer in photovoltaic application.

Origin of a Simultaneous Suppression of Thermal Conductivity and Increase of Electrical Conductivity and Seebeck Coefficient in Disordered Cubic Cu 2 ZnSnS 4

“…This hypothesis is further supported by absorption spectroscopy measurements (see SN 6 of the Supplemental Material [20]), which do not show significant differences between the band gap values of the two samples, suggesting that the improvement in carrier concentration is not connected with a reduction of the gap. Indeed, this is measured as 1.56 eV for the ordered tetragonal polymorph, in accordance with literature reports [36][37][38], and as 1.53 eV for the disordered cubic polymorph. The band gaps observed in the DFT band structures [Figs.…”

Synthesis and Characterization of Cu2ZnSnS4 Thin Films Obtained by Combined Magnetron Sputtering and Pulsed Laser Deposition

“…We notice that, after the heat treatment without sulfur, 2θ TR decreases slightly for all the films. The average mass density (ρ m ) of the thin films is proportional with (θ TR ) 2 , and accordingly, ρ m also decreases (Table 1). This fact, together with the decrease in the average thickness of all annealed CZTS thin films, means that the thin films undergo a process of partial evaporation and a reorganization of atoms, which produces the formation of voids between crystallites and a decrease in the thin-film thickness.…”

“…Cu 2 ZnSnS 4 (CZTS) is a strong material candidate for next-generation solar energy converters due to its high absorption coefficient and optimal band gap [ 1 ]. P-type chalcogenides are made of low-cost and earth-abundant elements (Cu, Zn, Sn, and S), unlike other thin-film solar cell technologies (CIS, CIGS, and CdTe) that contain expensive and/or toxic components [ 2 ]. Several physical and chemical routes can be used for the synthesis of CZTS thin films.…”

Topological Anderson Insulator in Cation-Disordered Cu2ZnSnS4

“…CZTS is a quaternary chalcogenide compound extensively investigated for its potential applications, primarily in photovoltaics [ 36 , 37 , 38 , 39 , 40 , 41 ], and recently thermoelectrics [ 28 , 42 , 43 , 44 , 45 , 46 , 47 ]. The most ubiquitous polymorph of CZTS is the kesterite structure ( Figure 1 a), which crystallizes in the tetragonal I-4 space group.…”