Author(s)

N. Severino, N. Bednar, N. Adamovic

Institute of Sensor and Actuator Systems, Technische Universitat Wien, Vienna, Austria.

This work investigates in-depth the effects of variation of the compositional ratio of the absorber layer in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. Electrical simulations were carried out in order to propose the most suitable gallium double-grading profile for the high efficiency devices. To keep the model as close as possible to the real behavior of the thin film solar cell a trap model was implemented to describe the bulk defects in the absorber layer. The performance of a solar cell with a standard CIGS layer thickness (2 μm) exhibits a strong dependence on the front grading height (decreasing band gap toward the middle of the CIGS layer). An absolute gain in the efficiency (higher than 1%) is observed by a front grading height of 0.22. Moreover, simulation results show that the position of the plateau (the region characterized by the minimum band gap) should be accurately positioned at a compositional ratio of 20% Ga and 80% In, which corresponds to the region where a lower bulk defect density is expected. The developed model demonstrates that the length of the plateau is not playing a relevant role, causing just a slight change in the solar cell performances. Devices with different absorber layer thicknesses were simulated. The highest efficiency is obtained for a CIGS thin film with thicknesses between 0.8 and 1.1 μm.

Solar Cell, Thin-Film, Simulation, Material Modelling

Severino, N. , Bednar, N. and Adamovic, N. (2018) Guidelines for Optimization of the Absorber Layer Energy Gap for High Efficiency Cu(In,Ga)Se₂ Solar Cells. Journal of Materials Science and Chemical Engineering, 6, 147-162. doi: 10.4236/msce.2018.64015.