## 3 Dielectric-Based Passivation Layers
### Solar Simulator Results  
In this sub-section, change in open circuit voltage (\(V_{oc}\)), current density (\(J_{sc}\)) and power conversion efficiency (\(\eta\)) values of the CIGS solar cells, before and after the implementation of the passivation approaches, will be given in detail. The \(V_{oc}\) and \(J_{sc}\), and the efficiency values of the studies given in Table 1 with respect to the thickness of the absorber layer are indicated in Figures 3 and 4, for both reference and passivated devices. Figure 3: (**a**) Current density (\(J_{sc}\)) and (**b**) open circuit voltage (\(V_{oc}\)) values, before and after introducing the passivation layer, with respect to thickness of the absorber layer. The yellow boxes are given to guide the eye. The green and blue stars represent the average values of passivated and reference devices in the given interval, respectively. For thick CIGS absorber layers (\(>\)800 nm), except for one study [24], the \(V_{\alpha c}\) was enhanced for all studies after the implementation of the passivation layer. For \(J_{sc}\) on the other hand, there were slight differences between reference and passivated devices for thick absorber layers (Figure 3). For the thickest CIGS absorber layer, i.e., 1.89 \(\upmu\)m, the difference between passivated and reference devices are hardly noticeable for \(V_{\alpha c}\) and \(J_{sc}\), but there is still an improvement [16]. On the other hand, for the thinnest CIGS absorber layer, i.e., 240 nm, there are clear improvements in both \(V_{\alpha c}\) and \(J_{sc}\), as expected [18]. The effects of the passivation mechanism are more observable for thinner CIGS absorber layers, as explained earlier. In order to address these effects, there are two yellow boxes in Figure 3. These boxes point out the interval between 0.3 \(\upmu\)m and 0.5 \(\upmu\)m. To make the outcomes of the studies in this interval clearer, the average of the \(V_{\alpha c}\) and \(J_{sc}\) of the reference and passivated devices is given with the star icons. The green stars belong to the passivated devices and the blue stars belong to the reference devices (Figure 3). According to the difference between blue (reference) and green (passivated) star icons in Figure 3a, introducing the passivation layer boosted the \(J_{sc}\) for thin/ultra-thin CIGS solar cells. Displayed as blue (reference) and green (passivated) star icons in Figure 3b, the gain in \(V_{\alpha c}\) can easily be observed for thin and ultra-thin CIGS solar cells. There are few outliers in the graphs that can be discussed. The first one is [17]. In this study, for the device which has a 600 nm thick absorber layer, they used low In and flat Ga. Hence, the \(J_{sc}\) is low for both the reference and the passivated device (\(\sim\)15 mA/cm\({}^{2}\) and \(\sim\)18 mA/cm\({}^{2}\), respectively). Although the \(J_{sc}\) was improved significantly after the implementation of the passivation layer, it was still lower than almost all of the other studies given in Table 1. The second outlier we want to discuss is [24], which used a 1 \(\upmu\)m CIGS absorber layer. In this study, the \(V_{\alpha c}\) values before and after the addition of the passivation layer were slightly lower than other studies that had thicker absorber layers, due to the lack of Na. In [24], for the reference sample, there was not an additional Na supply to enhance \(V_{\alpha c}\). For the passivated device, additional Na supply and Al\({}_{2}\)O\({}_{3}\) as a passivation layer were not sufficient to enhance \(V_{\alpha c}\) (Figure 3b). On the contrary, they were sufficient enough to enhance the \(J_{sc}\) (Figure 3a). Figure 4: Average power conversion efficiency (%) of CIGS solar cells with respect to thickness of the absorber layer before and after the addition of passivation layer. The green and purple ovals are given to guide the eye. After examining Figure 3, it can be concluded that after introducing a passivation layer with point contact openings, the electrical and/or optical properties of the CIGS solar cells were improved.