The optimization of optical properties for increased performance in a monolithic tandem dye-sensitized/Cu(In, Ga)Se2 solar cell

Tandem solar cells are an attractive solution to increase the performance of one or more low efficiency, low cost technologies into a more efficient device. This has been demonstrated previously using a physically stacked dye-sensitized and Cu(In, Ga)Se₂ or CIGS solar cell. The subsequent move to a monolithic design proved to be successful, however only delivering an efficiency of 12.2 % compared to the 15.1 % of the physical stack. This may have been due to optical losses and liquid electrolyte based instabilities on the ZnO:Al layer at the bottom CIGS cell interface. Besides this, shading is known to reduce the photocurrent and voltage in thin film solar cells. In a DSC/CIGS monolithic tandem, the shading caused from measuring the cell accurately with a mask to determine the precise DSC area, reduced the V_oc from 1221 mV to 848 mV, with a reduction in efficiency from 12.44 % to 7.75 %. It was discovered that the reduction of the CIGS active area in the tandem cell by altering the fabrication process led to a reduction in the difference between V_oc and efficiencies, with the masked tandem producing a V_oc of 1221mV and an efficiency of 9.38 % compared to a V_oc of 1287 mV and efficiency of 12.30 % when unmasked.