Effect of metal layer stacking order on the growth of Cu2ZnSnS4thin films

Abstract

In this paper we have presented an in-depth study of effect of metallic precursor stacking order on the growth of the Cu 2 ZnSnS 4 (CZTS) thin films. The CZTS films were prepared by employing a two-step process comprising of sequential sputtering of the metal precursors followed by sulfurization. An optimized stacking sequence as well as growth mechanism for obtaining the single phase CZTS has been proposed based on the results of XRD, Raman, XPS, UV-Vis and electrical studies. A combination of Raman analysis and XPS has been carried out to confirm the CZTS phase formation and to detect any minor phases, if present. The occurrence of Raman modes at around 286 and 336 cm-1 for the Zn/Cu/Sn/Cu stack sulfurized at 500 o C indicated the existence of prominent Kesterite CZTS phase. The perfect homogeneous mixing of sequential precursors together with the elemental sulfur was observed in the case of sulfurized stack order of Zn/Cu/Sn/Cu, and which yielded single phase CZTS films, which and further confirmed by high resolution core level XPS measurements. Stack dependent micro structural features and elemental analysis were also carried out using FESEM attached to EDS. The p-type charge carriers as detected using hot-probe measurement technique and the band-gap energy of ~1.52 eV as estimated from the absorbance spectrum, suggested that the Zn/Cu/Sn/Cu stack order is most appropriate for realizing single phase CZTS growth using two step method.

Fabrication of Efficient Cu2ZnSnS4 Solar Cells by Sputtering Single Stoichiometric Target

“…It demonstrates that all absorbers share a very similar pattern which agrees well with that of tetragonal kesterite CZTS (JCPDS No. 026-0575) with the preferred orientation of CZTS at (112) consistent with the literature [15,16]; the full width at half maximum (FWHM) of the main peak (112) of CZTS has a small dip down from 0.165 • to 0.158 • , then increases by 0.17 • and ends at 0.228 • with increasing the precursor deposition pressure from 5 to 12.5 mTorr. This FWHM trend is consistent with the SEM results as small FWHM reflects large grain size and a low defect level inside the film.…”

Impact of sulphurization environment on formation of $$\hbox {Cu}_{2}\hbox {ZnSnS}_{4}$$ Cu 2 ZnSnS 4 films using electron beam evaporated stacked metallic precursors

“…Su et al [15] fabricated CZTS films through sequential electrodeposition of metallic precursors and observed that the compositional ratio and stacking order have a major role in CZTS phase formation and they successfully prepared a 93% phase pure CZTS film with a glass/Zn/Sn/Cu precursor stack. Recent studies from Thota et al [20] and Olgar et al [21] also reveal that films having a Cu layer adjacent to both Sn and Zn layers have enhanced performance as an absorber layer due to the uniform diffusion of the precursor layers while annealing. Also, Thota et al [20] studied the effect of all the three constituent metallic layers as the capping layer and found that films with Cu at the top of stacking have enhanced electrical characteristics due to the minimal loss of volatile Sn and Zn from the precursor.…”

“…Recent studies from Thota et al [20] and Olgar et al [21] also reveal that films having a Cu layer adjacent to both Sn and Zn layers have enhanced performance as an absorber layer due to the uniform diffusion of the precursor layers while annealing. Also, Thota et al [20] studied the effect of all the three constituent metallic layers as the capping layer and found that films with Cu at the top of stacking have enhanced electrical characteristics due to the minimal loss of volatile Sn and Zn from the precursor. Kim and Yoo [13] also concluded that films prepared with Cu at the top have enhanced grain sizes which may lead to superior performance.…”

Electrodeposition of Tin onto Zinc for the Electrochemical Synthesis of Zn/Sn/Cu Precursor Stack for CZTS‐Based Photoconversion Devices

“…[11,12] On the other hand, almost no limitations were observed for vacuum-based processes allowing to exploit different stacking order combinations. [13][14][15][16][17][18][19][20][21][22] In this context, literature studies demonstrated the advantages that are achieved through alternative sequences. In fact, the evaporation of Zn and Sn during reactive annealing may result in the formation of voids and a significant variation in the film stoichiometry.…”

“…[23,24] The loss of the former is particularly critical since a zinc-rich copper-poor stoichiometry is associated with high-performing energy conversion devices. [24,25] Therefore, capping the zinc layer with Sn or Cu resulted in a lower evaporation rate and a more compact morphology, [13,[18][19][20] leading to a higher photoconversion efficiency. [13] Moreover, when Sn and Cu layers are adjacent, the formation of CuÀ Sn intermetallic and corresponding sulfides reduces the tin loss.…”