A Two-Step Magnetron Sputtering Approach for the Synthesis of Cu₂ZnSnS₄ Films from Cu₂SnS₃\ZnS Stacks

Abstract

Cu 2 ZnSnS 4 (CZTS) is regarded as one of the emerging materials for next-generation thin film solar cells. However, its synthesis is complex, and obtaining a single-phase CZTS thin film is difficult. This work reports the elaboration of Cu 2 ZnSnS 4 thin films by a sequential magnetron sputtering deposition of Cu 2 SnS 3 (CTS) and ZnS as stacked films. Initially, the CTS films were prepared on a soda lime glass substrate by annealing Cu and SnS 2 stacked layers. Second, ZnS was deposited by magnetron sputtering on the CTS films. The CTS\ZnS stacks were then annealed in Sn + S or S atmospheres. The tetragonal CZTS structure was obtained and confirmed by grazing incidence X-ray diffraction and Raman spectroscopy. The morphological and compositional characteristics, measured by scanning electron microscopy and energy-dispersive spectroscopy, revealed large grains and dense surfaces with the elemental composition close to the intended stoichiometry. Additional X-ray photoemission spectroscopy measurements were performed to determine the surface chemistry and particularities of the obtained films. The optical properties, determined using conventional spectroscopy, showed optimal absorber layer band gap values ranging between 1.38 and 1.50 eV. The electrical measurements showed that all the films are p-type with high carrier concentrations in the range of 10 15 to 10 20 cm –3 . This new synthesis route for CZTS opens the way to obtain high-quality films by an industry-compatible method.

Study of optical and structural properties of CZTS thin films using copper capping layer and sulfurization to correct stoichiometry

“…The measurement revealed that all samples are p type and possess a positive Hall coefficient. The charge carrier concentration for the samples S-2, S-3, and S-4 was of the order of 10 , 21 as shown in table 5, which is much higher than any reported values. High carrier concentration is owing to addition of copper capping layer.…”

“…There are two ways that researchers have reported for sputter deposition of CZTS thin films; either from a composite target [18,19], or multilayer thin films using multiple targets [20]. The sputter deposited layer stack of CTS and ZnS was used by Zaki et al [21] to produce CZTS thin films. Authors found that, in CTS layer when copper is used as a capping layer, produced better CTS films than SnS 2 on top.…”

Recent Progress and Challenges in Controlling Secondary Phases in Kesterite CZT(S/Se) Thin Films: A Critical Review

“…On the other hand, the identification of SnS and SnS 2 secondary phases in CZTS films is facilitated through various SEM and EDS observations. Zaki et al, detected the presence of larger white particles, exceeding the size of CZTS grains, corresponds to the SnS 2 secondary phase, as confirmed by EDS mapping and shown in Figure 11 [65]. In other studies, SEM images reveal sheet-like structures identified as SnS 2 on the surface of CZTS films, EDX mapping further substantiates the presence of Sn and S elements in the identified sheet-like grains [108,109].…”

“…On the other hand, the SnS 2 is easily distinguished with a peak at around 2θ = 50 • in the films annealed in Sn+S atmosphere, due to excess in Sn. Contrarily, the CuS (2θ = 31.97 • ) phase was observed in one of the sulfurized (annealed in S only) CZTS films, due to the Sn-poor composition of the film as observed in Figure 7 [65]. The case of copper sulfides such as CuS and Cu 2 S is different, since they can be easily identified through XRD, as their unique diffraction peaks (2θ = 31.88 .…”

“…In certain studies, researchers have employed a two-step deposition strategy, involving the sequential deposition of Cu 2 SnS 3 or Cu 2 SnSe 3 followed by a layer of ZnS or ZnSe as presented if Figure 11a-c). Various techniques, including hydrothermal [126], spray pyrolysis [127], chemical bath deposition [128], sonochemical reactions [129], and magnetron sputtering [65,87], have effectively employed a two-step synthesis process. This innovative approach is effective in mitigating secondary phases when the process is meticulously optimized.…”