## 4 Conclusions  
To solve the problems associated with the conventional selenization method of toxicity, high cost, and an environmentally unfriendly process for preparing an absorber layer of CIGS thin-film photovoltaics, several investigations were conducted on CIGS thin films fabricated through an annealing process after the sputtered precursors. However, even though the RTA process was performed, the thin-film properties were degraded because of the deterioration of crystallinity due to the lattice defects caused by the highly volatile Se. Therefore, the purpose of this study was to improve the crystallinity by compensating for the stoichiometry of the CIGS thin films through the RTA process after the co-sputtering of Te with CIGS. In the prepared CIGS:Te thin films, the compositional ratio did not increase linearly with the co-sputtering time, and the relative atomic ratio and compositional ratio of Te in the CIGS:Te thin films were small, and the amount of change was not large. However, significant changes were observed in the crystallinity in the XRD analysis and the surface properties in FESEM; when the deviation parameter (\(\Delta\)s) from the stoichiometry and normalized stoichiometric deviations were examined in this study, the results were largely consistent with the behaviors of thin-film properties. Under conditions where \(\Delta\)s was small and/or the normalized stoichiometric deviations of Se + Te and In + Ga were close to stoichiometric, the crystallinity of the CIGS:Te thin films was excellent, such as large grain size and clear grain boundaries, and the microstrain/dislocation density was the lowest, resulting in the largest volume of the unit cell. The optical properties of the CIGS:Te thin films as an absorber were also excellent compared to those of the CIGS thin film, with \(E_{g}\) = 1.548 eV. These were able to compensate for Se vacancies with appropriate co-sputtering of Te, which was confirmed through Hall-effect analysis to be the result of achieving the smallest number of defects while securing the best stoichiometry with the lowest carrier concentration (Se vacancies). Thus, the manufacturing improved-crystallinity CIGS:Te thin films without selenization using the proposed method can improve the efficiency of CIGS thin-film photovoltaics and advance their commercialization. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13074284/s1](https://www.mdpi.com/article/10.3390/app13074284/s1)]([https://www.mdpi.com/article/10.3390/app13074284/s1](https://www.mdpi.com/article/10.3390/app13074284/s1)), Figure S1. (a) Schematic diagram of the co-sputtering deposition process with different Te co-sputtering times of (1) 0, (2) 270, (3) 510, (4) 750, (5) 945, and (6) 1140 s to prepare CIGS:Te thin films with a total thickness of 400 nm considering the deposition rates of Te and CIGS. All precursors were transferred to a rapid thermal annealing (RTA) system and subjected to heat treatment at 400 \({}^{\circ}\)C for 20 min under ambient N\({}_{2}\). (b) Temperature-time profile of the RTA process for 20 min at 400 \({}^{\circ}\)C. Figure S2: Cross-sectional field emission scanning electron microscopy (FESEM) images of the CIGS:Te thin films with Te co-sputtering times of: (a) 0, (b) 270, (c) 510, (d) 750, (e) 945, and (f) 1140 s, corresponding to (a) 414, (b) 417, (c) 409, (d) 405, (e) 401, and (f) 397 nm, respectively. Note the different magnification of the images from (a). Conceptualization, S.P., Y.J.R. and N.-H.K. ; investigation, S.P. and Y.J.R. ; data curation, S.P., Y.J.R. and K.-Y.L. ; writing--original draft preparation, S.P., Y.J.R. and S.K. ; writing--review and editing, S.K., K.-Y.L. and N.-H.K. ; project administration, N.-H.K. ; funding acquisition, N.-H.K. All authors have read and agreed to the published version of the manuscript. This study was supported by a research fund from Chosun University, 2022. Not applicable. Data Availability Statement: Data are contained within the article or supplementary material.