CZTS / CdS / ZnO / ITO solar cell was studied using Solar Cell Capacitance Simulato-1D (SCAPS-1D) program. We performed an improvement on the theoretical cell by increasing the doping and thickness of some layers. As a result, the efficiency was shifted from 2.18% to 6.17% and several back reflection layers (BSL) were introduced on the enhanced cell until. We obtained a highest conversion efficiency of 13.99%.  The best reflection layer (CZTSSe) was combined with the best buffer layer (CdSe), with thickness of 0.9µm, on the enhanced cell. Thereby, we obtained a cell with a conversion efficiency of 16.53%. A second improvement was made to the best obtained cell, where the CZTSSe with thickness of 0.05µm and the CdSe with thickness of 0.9µm were combined. Consequently, the efficiency was increased from 16.53% to 21.76%. By comparing the experimental results with those obtained with the program, it was found that the program simulates reality, i.e. the experimental and theoretical results matched.

The ZnO/ZnS/ CNTS solar cell was studied using SCAPS-1D simulation. The cell efficiency was 9.38% and to improve the cell a back reflection layer (BSL) was added, so the conversion efficiency increased to 10.65% and we entered buffer layers, thus the cell structure became ZnO / Buffer / CNTS the conversion efficiency increased to 10.78%. It turns out that the effect of the buffer layer is greater than the reflection layer. The best cell was ZnO/CdS/CNTS/Cu2O and the conversion efficiency was 12.09%, fill factor 62.98%, short circuit current 20.01 mA/cm2 finally open circuit voltage 0.95V.