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We performed an investigation on the behaviour of the electrical parameters of ultrathin Cu(In,Ga)Se 2 (CIGS) solar cells buffered with Zn(O,S). Using one-dimensional simulations and by defining a new structure, we achieved a significant reduction of the absorber and the buffer layers to evaluate the changes in the cell’s performance. The simulation results revealed that a good optimisation of the thickness and sulphur content of the Zn(O,S) buffer layer could be an ingenious way to reduce the thickness of the absorber without compromising the performance of the solar cells. A high efficiency of 16.9% is obtained for 0.5 μ m of the absorber layer when the thickness and sulphur content of the Zn(O,S) layer are 10 nm and 0.9 respectively. At this configuration, we introduced p + -CIGS and SnS layers at the CIGS/Mo interface as back surface field (BSF) to reduce interface recombinations, which are very predominant in ultrathin absorber. An improvement of 2% and 5.96% on the efficiency is obtained with the p + -CIGS and SnS layers respectively. The shape of the band diagram shows good alignment and low band bending at the CIGS/OVC/Zn(O,S) interfaces and the corresponding conduction band offset is + 0.2 eV between the CIGS and the Zn(O,S) layers. Ultrathin CIGS and Zn(O,S) layers can be helpful in improving the stability of the cell with regard to the results obtained from the electrical parameters. [ABSTRACT FROM AUTHOR]