## 3 Results and Discussion
In the case of Cu, negative values were observed under all conditions except (6), and the deviation was in the range of \(-\)3.58-0.79. The deviations for In + Ga and Se + Te were in the ranges of +3.52 to +4.74 and \(-\)0.06 to \(-\)5.49, respectively, under all conditions where Te was sputtered, as shown in Figure 2b. The effects were more clearly investigated when each deviation was normalized for the ideal stoichiometry, as plotted in Figure 2e. The CIGS thin film prepared via RTA after sputtering had many Se vacancies in a Se-poor state, as shown in Figure 2e; however, the normalized stoichiometric deviation for Se + Te was close to ideal stoichiometry under condition (3) once stoichiometric compensation was performed by Te co-sputtering, while it was the largest under condition (6). Although it could not be confirmed in Figure 2b,d, the normalized stoichiometric deviation for In + Ga also changed dramatically, as shown in Figure 2e. Under all conditions, In + Ga was in a surplus state and showed the largest deviation in the CIGS thin film (condition (1)), but after the Te co-sputtering, even the In + Ga changed more closely to stoichiometry in all the CIGS:Te thin films. In particular, In + Ga was in the smallest excess state under condition (3) and changed to the most non-stoichiometric deviation under condition (6) of the CIGS:Te thin films. The normalized stoichiometric deviation of each element group showed a similar tendency to change, with CIGS thin films being the most non-stoichiometric, while the most stoichiometric and non-stoichiometric compositions were obtained under conditions (3) and (6) of the CIGS:Te thin films, respectively. Figure 3a shows the XRD patterns of the RTA-treated CIGS:Te thin films at different co-sputtering times for the Te target in the 2\(\theta\) range of 10\({}^{\circ}\)-90\({}^{\circ}\). The XRD patterns exhibited an enhanced crystalline quality in the CIGS:Te thin films without selenization after 20 min of RTA treatment at 400 \({}^{\circ}\)C, which did not contain any appreciable amounts of elemental phases or secondary phases such as Te and InTe after the RTA treatment [25]. This is believed to be because Te atoms replace Se vacancies, and all samples show (Se + Te)-poor conditions,  
Figure 2: Energy dispersive X-ray spectroscope (EDX) analyses of the CIGS:Te thin films with different Te co-sputtering times of (1) 0, (2) 270, (3) 510, (4) 750, (5) 945, and (6) 1140 s. (**a**) Thickness ratio and atomic percent, (**b**) relative atomic percentage, (**c**) compositional ratio, (**d**) deviation parameters from the molecularity and the stoichiometry, \(\Delta m\) and \(\Delta s\), and (**e**) normalized stoichiometric deviations. leaving no extra Se or Te atoms to appear in the form of elemental phases or secondary phases. The CIGS:Te thin films showed major diffraction peaks corresponding to the CIGS chalcopyrite phases with preferred orientations of (112), (220/204), and (312) at 2\(\theta\) = 26.71\({}^{\circ}\), 44.28\({}^{\circ}\), and 52.47\({}^{\circ}\), respectively. The major diffraction peaks became sharper and stronger under condition (3). Closest to the stoichiometric composition under condition (3), the normalized stoichiometric deviation for Se + Te was observed to have a greater impact on the crystallinity. The major diffraction peaks were also observed to become less sharp under condition (6), which has the highest (Se + Te)-vacancy and the highest In + Ga surplus. As shown in Figure 2b,c, the change in the relative atomic percentage and compositional ratio was not significant under condition (6). The diffraction peaks of the CIGS:Te thin films under these conditions indicated that grain growth and crystallinity of the thin films occurred along the (112)-, (220/204)-, and (312)-oriented crystallographic CIGS planes. This confirms that Te co-sputtering can achieve good crystallographic quality and grain growth because Te fills the Se vacancies to reduce crystal defects.