A low-cost, sulfurization free approach to control optical and electronic properties of Cu2ZnSnS4 via precursor variation

Abstract

Thin films of Cu2ZnSnS4 (CZTS) were synthesized via a low cost, wet chemical technique of chemical bath deposition (CBD). In the first part of this study, the chemical composition ratio S/(Cu+Zn+Sn) was varied keeping Cu/(Zn + Sn) and Zn/Sn ratios constant to study the effect of sulfur variation. Detailed electrical and optical characterization has been carried out using UV-Vis spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy and Kelvin probe force microscopy (KPFM) techniques. The results of the present study confirm that near ideal stoichiometry could be achieved in CZTS by adding excess thiourea in a controlled manner which eliminates the need for the normally used post-synthesis and high temperature sulfurization step. Using the stoichiometric sample as the basis, in the second part of the study Cu/(Zn+Sn) and Zn/Sn was varied and it was found that the electronic properties of CZTS in terms of band gap, work function and valence band edge position could be controlled by precursor variation. The Cu-poor, Zn-rich samples showed a better photoresponse which has been attributed to a decrease in the CuZn type defects. The study thus demonstrates a scalable and low-cost technique to grow CZTS absorber layers for solar cells with control over its electronic properties which is important for effective device operation.

Achieving Low VOC-deficit Characteristics in Cu2ZnSn(S,Se)4 Solar Cells through Improved Carrier Separation

“…26 However, decreased Sn concentration in V3 and V4 (Figure 4c,d) reduces this number of clusters. 27,28 This trend is consistent with the previous literature. 27 Figure S8 shows the average CPD at GBs and GIs and the CPD difference between GBs and GIs extracted from CPD spatial maps.…”

“…27,28 This trend is consistent with the previous literature. 27 Figure S8 shows the average CPD at GBs and GIs and the CPD difference between GBs and GIs extracted from CPD spatial maps. Figure 4f shows the histogram plots of clusters from each sample.…”

“…Considering the work function of CZTSSe, CPD peaks shift to lower CPD values of −0.11, −0.13, −0.15, and −0.22 V for samples V1–V4, respectively (Figure e). It indicates that the decreased Sn concentration from V1 to V4 increases the work function of the sample (Φ sample = Φ tip (5.1 eV) + CPD), owing to excess Cu and reduced Zn, which in turn contributes to shifting the Fermi level into the valence band. , This trend is consistent with the previous literature Figure S8 shows the average CPD at GBs and GIs and the CPD difference between GBs and GIs extracted from CPD spatial maps.…”

Ambient-Air Sulfurization Process for Cu2ZnSnS4 Thin Film Solar Cells: Self-Creating Inert Atmosphere Using Sulfur Vapor

“…It indicates that CZTS thin films can absorb most of the light in visible range. The band gap of the CZTS thin film was further calculated by linear extrapolation of (αhν) 2 versus hν from the transmittance spectrum, 10 resulting in a band gap of 1.57 eV (Figure 6(b)).…”

Novel Evaporation Process for Deposition of Kesterite Thin Films Synthesized by Solvothermal Method

“…Some of these deposition methods already reported are roll to roll process [6] and spray coating [7]. (3) Finally, research about methods used for simultaneous synthesis and deposition of several materials over the substrate [8][9][10]. In the present work are reported CZTS compounds synthesized by using the solvothermal method and deposited over a substrate by thermal evaporation.…”