An interdigitated back-contacted (IBC) configuration is proposed for submicron cop-per indium gallium (di)selenide (CIGS). In a modelling platform, the structure wasopto-electrically optimized for maximum efficiency. The results are compared with areference front/back-contacted (FBC) solar cell with similar absorber thickness andexhibiting 11.9% efficiency. The electrical passivation at the front side is accom-plished by an Al2O3layer, which is endowed with negative fixed charges. The resultsindicate that with an optimal geometry and engineered bandgap grading, the effi-ciency of the new IBC structure can reach 17%. Additionally, with a reasonably lowdefect density in the absorber layer, efficiencies as high as 19.7% and open-circuitvoltage comparable with that of the record solar cell are possible with the IBCstructure.