## 5 Conclusions  
We numerically investigated the effect of the incoherent encapsulation layer and oblique sunlight incidence on the reflectance spectra and J-V curves of surface-textured CIGS solar cells. The optical modeling of the two incoherent encapsulation layers was performed based on the proposed ADETAM, which provided the incident-angle-dependent reflectance spectra of the mixed coherent-incoherent planar and surface-textured CIGS solar cells. The calculation accuracy of the ADETAM was verified in a planar CIGS solar cell through a very good agreement with exact analytical results obtained by the GTMM. In addition, The J-V curve of the CIGS solar cell was calculated based on the 2D FEM-based numerical solution of the drift-diffusion model. To investigate the effect of the front incoherent encapsulation layers on output performance of the CIGS solar cell, the angular dependences of reflectance spectrum and J-V curves were calculated and compared in both planar and surface-textured CIGS solar cells with and without the inclusion of the two front encapsulation layers. The calculated reflectance of the planar CIGS solar cell with the front encapsulation layers was greater than that of the planar CIGS solar cell without the front encapsulation layers because the refractive-index difference between the air and the cover glass was less than the refractive-index difference between the air and the AZO TCO. In contrast, the calculated reflectance of the surface-textured CIGS solar cell with the front encapsulation layers was lower than that of the surface-textured CIGS solar cell without the front encapsulation layers. This was ascribed to the fact that the reflectance of the surface-textured CIGS solar cell with the front encapsulation layers, which was determined by the incoherent multiple optical reflections, was greater than that of the surface-textured CIGS solar cell without the front encapsulation layers, where the significant reflectance reduction caused by light scattering effect occurred at the surface-textured interface between the air and the AZO TCO. Correspondingly, the improvement percentages of J\({}_{\text{SC}}\) in the surface-textured CIGS solar cell over the planar CIGS solar cell with the front encapsulation layers are lower than that of the surface-textured CIGS solar cell with the front encapsulation layers. Figure 11: Calculated J–V characteristics of the surface-textured CIGS solar cell without and with the inclusion of the front incoherent layers. For reference, the J–V characteristics of the planar CIGS solar cell are also calculated. The incidence angle of the AM 1.5 sunlight is \(\theta_{0}\) = (**a**) 0\({}^{\circ}\), (**b**) 30\({}^{\circ}\), (**c**) 45\({}^{\circ}\), and (**d**) 60\({}^{\circ}\), respectively. in the surface-textured CIGS solar cell over the planar CIGS solar cell without the front encapsulation layers. Thus, the output performance of the surface-textured CIGS solar cell over the planar CIGS solar cell can be over-predicted when the thick encapsulation layers are not considered in the optoelectronic modeling. We expect that the proposed ADETAM, together with comprehensive numerical modeling and analysis, will give a deeper understanding on the simultaneous effect of the thick front encapsulation layers and oblique sunlight incidence on output performance of the CIGS solar cells and help to provide a more efficient optical design of thin-film CIGS solar cells in the consideration of realistic deployment situations. Conceptualization, J.K. ([PERSON]); methodology, G.L. and J.K. ([PERSON]); software, G.L., J.K. ([PERSON]) and S.K. ; validation, G.L., J.K. ([PERSON]), S.K. and J.K. ([PERSON]); formal analysis, G.L., S.K. and J.K. ([PERSON]); investigation, G.L. and J.K. ([PERSON]); writing--original draft preparation, J.K. ([PERSON]); writing--review and editing, G.L., J.K. ([PERSON]), S.K. and J.K. ([PERSON]); visualization, G.L. and J.K. ([PERSON]); supervision, S.K. and J.K. ([PERSON]); project administration, S.K. and J.K. ([PERSON]); funding acquisition, S.K.