The suppressing of excitonic effects in Cu-chalcogenides for solar cell applications.

• Excitonic effects in Cu-chalcogenides are explicitly calculated by the Bethe-Salpeter equation (BSE) • Electronic mechanism of the moderate-strength excitonic binding. • Justification of a simple single-particle approach for reproducing the experimental observations. Excitonic effect can usually significantly enhance the optical absorption coefficient in wide-gap insulators. Cu-chalcogenides are widely used as thin-film solar cell absorbers due to their high light utilization efficiency. Theoretical investigations on the excitonic absorption in Cu-chalcogenides are rare because of the complicated two-particle nature of an exciton. Here, we theoretically evaluate the continuum-excitonic effect in CuGaS 2 and CuInS 2 by solving the Bethe-Salpeter equation. Despite the large bandgap of 2.4 eV for CuGaS 2 , the excitonic effect induces moderate absorption enhancement when compared with the single-particle scenario. Moreover, the experimental results are better reproduced using the latter approach, indicating that the intrinsic excitonic effect is nearly suppressed in the practical experiments. The moderate intrinsic excitonic effect and its further suppressing in the experiments are explained by strong electronic screening effects in these materials. Justification of the simple single-particle approach would be convenient for future theoretical studies, which otherwise require more complex methods with more expensive computational efforts. [ABSTRACT FROM AUTHOR]