Numerical Modelling and Analysis of the Spectral Response and Performance of Single-Junction InGaN Solar Cells Under Monochromatic Illumination

In this work, a comprehensive numerical study of the optoelectronic properties of a single-junction photovoltaic (PV) solar cell is presented. The influence of the indium composition, active-layer thickness, and illumination wavelength on the device performance parameters is investigated. The results show that increasing the illumination wavelength broadens the spectral response and enhances optical absorption, with the absorption coefficient reaching for x ≈ 1. However, for indium compositions above 0.5, degradation of the crystalline quality leads to an increase in Shockley–Read–Hall non-radiative recombination, reducing the effective carrier generation rate g (cm -3 ·s -1 ) despite the improved optical absorption. Analysis of the photocurrent and output power reveals an optimal base thickness of 1.5 µm, beyond which recombination losses become dominant. The external quantum efficiency exhibits a minimum value of 94.7% around x ≈ 0.2 before increasing to 97.1% for indium-rich compositions, indicating that absorption becomes increasingly concentrated within the depletion region, thereby enhancing carrier collection. Current–voltage characteristics show a gradual decrease in the open-circuit voltage from 2.793 V to 2.245 V and a slight reduction in current from 0.0679 A to 0.06658 A as x increases from 0.1 to 0.2, highlighting a fundamental trade-off between optical absorption and output voltage. A maximum power conversion efficiency of approximately 28% is achieved for x ≈ 0.13 at an illumination wavelength of λ = 0.68 µm. These findings identify the optimal operating conditions of the device and provide valuable insights for the design of high-efficiency InGaN multi-junction solar cells.