Analytical model for photocurrent density in linearly graded band gap Sb2Se3 solar cells

Abstract

This study introduces a model to estimate the photocurrent density in Sb₂Se₃ solar cells with a linearly graded band gap, adaptable for various grading profiles. The model incorporates both carrier generation and recombination processes, along with an effective absorption coefficient, to more accurately compute the photocurrent density. Our results show that band gap grading leads to higher photocurrent densities compared to non-graded cells, offering design flexibility for improved device performance. Specifically, the graded band gap reduces sensitivity to band-gap changes, allowing for enhanced built-in voltage and back surface field effects. We identify an optimal grading strength that maximizes photocurrent density, while excessive grading reduces absorption efficiency. Additionally, longer diffusion lengths contribute to higher photocurrent densities, though recombination in the depletion region has a more pronounced effect than in the absorber. These findings suggest that controlled band gap grading in Sb₂Se₃ solar cells can significantly enhance their efficiency.