Abstract. This work explores the photovoltaic performance of a high efficiency heterostructure based on CIGS solar cells using SCAPS. Various electrical specifications were explored at various thicknesses and doping densities. Initially, photovoltaic characteristics of the ITO/GaSe/CIGS heterostructure are investigated. The results show an optimized PCE of 22.59%. Then, a thin film strongly doped p-type is employed
(CIGS-p⁺) to the structure. The engagement of the CIGS-p⁺ layer increases the PCE to 31.94%. The proposed CIGS-p⁺ layer is interpreted to serve as a back surface field. The structure is further improved by adding a third interfacial layer of p-MoS₂ transition metal dichalcogenide material between the absorber and the Mo back contact. Adding a third interfacial layer implied an efficiency increase of 34.55%. The results reveal that the MoS₂ layer at the CIGS/Mo interface adapts it creating Schottky-type contact to quasi-ohmic contact. The results confirm the beneficial influence of the interface layers on the CIGS heterostructure. Additionally, the performance of the photovoltaic cell against the defect intensity of the absorber layers is found to degrade behind a level of 1 ×
10¹⁸ cm^–3. An ITO/GaSe/CIGS/CIGS-p⁺ based structure exhibited the highest stability in performance against the temperature change among the three examined systems.

Key words: SCAPS simulation, CIGS, CIGS-p⁺, TFSCs, defect density.