Black silicon (b-Si) is considered as an ideal material for optoelectronic devices due to its better optical, electrical, and intrinsic properties, such as high surface-to-volume ratio, ultralow light reflection, high chemical activity, and super hydrophobicity. In addition, b-Si materials demonstrate lower band reflection and hence, are used in solar cells as anti-reflective surfaces. Thermal annealing in optoelectronic device processing is known to be standard and crucial fabrication steps; there is a trade-off with device characteristics, which is the case for b-Si. In this experimental investigation, we report the influence of thermal annealing treatment on the optical and structural properties of the b-Si layers fabricated using the plasma-based reactive ion etching method. The results demonstrate that structural properties, i.e., average height, surface enhancement factor, and root mean square roughness of b-Si layers after annealing at different temperatures changed quite significantly. This leads to deterioration of optical properties like reflection and absorption of b-Si layers. Finally, a new fabrication process of b-Si solar cells is proposed and tested. According, the b-Si layer is grown after the high-temperature diffusion process. The results of this study show that the new b-Si solar cell performance parameters are improved compared to that of the conventional solar cell. This can increase b-Si material extension to other applications.