Investigation of light trapping and NiOx anti-reflection layer in ultra-thin crystalline silicon by ray tracer

In this work, the optical characterizations based on ray tracing for ultra-thin crystalline silicon (c-Si) (20 μm absorber thickness) solar cells with various surface structures are investigated. Ray tracing is commonly used to analyze the microstructure of light trapping structures in ultra-thin c-Si solar cells. Various surface structures include the front nickel oxide (NiOx) anti-reflectance (AR) layer with front inverted pyramids of the ultra-thin c-Si in the spectral range of 300–1100 nm. A flat ultra-thin c-Si absorber (without a NiOx AR layer and inverted pyramids) is used as a reference. The transmittance, reflectance, and absorbance of the ultra-thin c-Si are calculated using ray tracing. The output parameters from optical simulation, such as the weighted average surface reflectance (R_w) and generation current density (J_G) are used as the metric to be optimized. The NiOx layer on inverted pyramids with ultra-thin c-Si gives the lowest R_w (0.10) and therefore illustrates the highest potential J_G of 38.11 mA/cm². This corresponds to 16.7 mA/cm² enhancement when compared to the ultra-thin c-Si reference. Then, the potential J_G from the best surface structure is compared with the Lambertian absorbance in the 20 μm ultra-thin c-Si substrate. Therefore, the inverted pyramids with the NiOx AR layer are a promising way to minimize the front surface reflectance of ultra-thin c-Si, which can be attributed to the refractive index grading effect at the air and NiOx /microtextured interface. The findings from this work illustrate the potential of ultra-thin c-Si as a promising photovoltaic (PV) technology for the future.