Bandgap Engineering and Distinct Gradings in Cu(In, Ga)Se ₂ Thin Films for Enhanced Photovoltaic Performance

This study investigates the role of compositional grading in enhancing the performance of Cu(In, Ga)Se 2 (CIGS) thin‐film photovoltaic devices. Owing to its tunable bandgap (1.04–1.68 eV), CIGS enables controlled bandgap engineering through variation of the Ga/In ratio across the absorber layer. Such grading introduces internal electric fields that facilitate efficient charge separation and suppress carrier recombination, thereby improving device efficiency. To systematically analyze these effects, seven distinct profiles, such as linear, parabolic, parabolic‐2, logarithmic, power‐law, beta function, and exponential, were simulated using SCAPS‐1D. The results demonstrate that such distinct grading effectively minimizes thermalization and transmission losses while enhancing spectral response by optimizing the bandgap distribution throughout the absorber. Among the studied profiles, the power‐law grading exhibited the highest efficiency enhancement (~33.31%) under high shallow acceptor density, the exponential profile achieved the maximum open‐circuit voltage (~1.04 V), and the parabolic‐2 profile delivered the highest fill factor (>82%) along with an improved short‐circuit current density compared to the ungraded device. These findings highlight bandgap grading as a promising strategy for advancing high‐efficiency CIGS‐based tandem photovoltaics.