## 3 Results and Discussion  
Before the simulation of the textured layers, the flat-layered solar cells with different thicknesses of CIGS absorbers were simulated. The decrease of the optical absorption in the absorbers with thicknesses ranging from standard 2000 nm to ultra-thin 250 nm is presented in Figure 2. As expected, the largest absorption decrease is present in the higher wavelength region, since the absorption of the CIGS material is the lowest in this spectral region. Figure 1: Used model geometry; (**left**) triangular and (**right**) convex texture features, with two variable parameters: texture height (_h_) and width (_d_). Figure 2: Absorption in the Cu(In,Ga)Se\({}_{2}\) (CIGS) absorber layer with the varying thickness. In all of the following simulations a 500 nm thick absorber layer was considered. An example of triangular texturing, with the texture period \(d=400\) and variable height \(h\) is presented in Figure 3. Based on Equation (1) the absorption within the CIGS layer was calculated and presented in Figure 3a,b for TE and TM polarized excitations, respectfully. It can be observed that the absorption was significantly increased over the majority of the wavelength spectrum in the case of TM polarization. Especially high is the enhancement at 550 nm. The absorption increases with the rise of texture aspect ratio. For the wavelengths in the range between 830 and 1000 nm there is no visible change of absorption. In the case of TE polarization the enhancement was observed for the longer wavelengths in the range of 800-1050 nm, as well as in the narrow window between 400 and 470 nm. In the wavelength range between 470-750 nm a decrease of the absorption can be observed. This may be contributed to the increased absorption within the transparent conductive oxide (TCO) layer due to the elevated interference in that specific wavelength range. While the absorption rises with the aspect ratio also in the case of TE polarization, in the window of 470-750 nm the decrease of the absorption is more prominent at the higher aspect ratios. Figure 3: Absorption of the CIGS absorber layer with the use of triangular structuring, with texture period of 400 nm and variable height. (**a**) transverse-electric (TE) polarization; (**b**) transverse-magnetic (TM) polarization; (**c**) average polarization; (**d**) average polarization scaled to AM1.5 solar irradiance spectrum. The average value of the absorption was calculated as \(P_{\mathrm{absAVG}}=(P_{\mathrm{absTE}}+P_{\mathrm{absTM}})/2\). Figure 3c shows the average absorption in the absorber layer of the considered textured device. The practical contribution of the light trapping can be seen on the absorption enhancement diagram scaled to the referent AM1.5 solar irradiance spectrum presented in Figure 3d. It can be seen that the highest impact of the textured layers is on the absorption within the range of 400-600 nm. Large absorption enhancement is also present in the high wavelength range 1000-1100 nm. However, due to the poor absorption capabilities of CIGS material in these wavelengths, the contribution of the absorption enhancement in this range does not have such significant effect on the total enhancement of absorption. Figure 4 presents the electric field strength within the layers of the cell with the texture dimensions \(h=300\) nm and \(d=400\) nm. In order to better assess the origin of absorption enhancement in the CIGS layer, the absorption in the other layers was also investigated. Figure 5 presents absorption in all device's layers, excluding the buffer layer since it was observed that the texturing of the device does not have a noticeable effect on the absorption within this layer. The total device's reflection was comparatively presented in the same figure. Besides the flat device, two textured devices' layers absorption properties were shown: \(d=400\) nm and \(h=200\) nm, and \(d=200\) nm and \(h=100\) nm. Both of these devices possess the same texture aspect ratio.