Thin film solar cells with graded-bandgap photon-absorbing layer

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 Cu(In, Ga)Se2 (CIGS), Cu2ZnSn(S, Se)4 (CZTSSe), and (Al, Ga)As (AlGaAs) photon-absorbing layer for optimizing the power-conversion efficiency of thin-film CIGS, CZTSSe, and AlGaAs solar cells, respectively. The coupled optoelectronic model-predicted an efficiency of 27.7% with a 2200nm-thick CIGS photon-absorbing layer for the CIGS solar cell, 21.74% with a 870nm-thick CZTSSe layer for the CZTSSe solar cell, and 34.5% with a 2000nm-thick AlGaAs layer for the AlGaAs solar cell. Also optimized was a CIGS–CZTSSe solar cell, with bandgap graded in both the CIGS layer and the CZTSSe layer, and an efficiency of 34.45% was predicted with a 300nm-thick CIGS layer and a 870nm-thick CZTSSe layer. The model-predicted results are expected to provide impetus to devise efficacious techniques for bandgap grading for ubiquitous small-scale harnessing of solar energy, for example, to power IoT (Internet of Things) devices.