Optoelectronic Modeling of Graded-Bandgap Thin-Film Solar Cells

Thin-film solar cells are cheap and easy to manufacture but require improvements as their efficiencies are low compared to that of the commercially dominant crystalline-silicon solar cells. A coupled optoelectronic model was formulated and implemented along with the differential evolution algorithm to assess the efficacy of grading the bandgap of the absorber layer in three thin-film solar cells. Optimal grading was predicted to yield efficiency of 21.1% with a 2200-nm- thick CIGS absorber layer for the CIGS solar cell, 21.14% with a 870-nm-thick CZTSSe layer for the CZTSSe solar cell, and 34.5% with a 2000-nm-thick AlGaAs layer for the AlGaAs solar cell. For a solar cell with two bandgap-graded absorber layers, an efficiency of 34.45% was predicted with a 300-nm-thick CIGS layer and a 870-nm-thick CZTSSe layer. For colored solar cells, efficiency loss was predicted from 10% to 20%, depending upon the percentage of incoming solar photons rejected.