Laser-assisted Nano-texturing for Flexible Ultrathin Crystalline Si Solar Cells

Abstract Ultrathin crystalline Si wafers, which are more flexible than conventional ones, can apply to curved surfaces, enabling a wide range of applications such as building integrated photovoltaics, vehicle integrated photovoltaics and wearable devices. Thinner wafers require more effective light trapping; thus, surface texturing in microscale is a common approach to compensate for the reduced thickness by enhancing the light pathlength. Microscale textures, however, deteriorate the mechanical flexibility due to stress concentration in the valley of the micro-textures. In this study, we propose a laser-assisted nano-texturing process for enhanced flexibility of the ultrathin Si solar cells with a 50-µm thickness while maintaining light trapping performances. A nano-lens array was used to focus laser onto the Si wafers, inducing the formation of nanoparticle etch masks for nano-pyramid texturing in an alkaline solution. The origin of the enhanced flexibility of the nano-textured Si wafers was discussed by a micro-mechanics simulation study. We applied our nano-texturing technique to ultrathin Si based PERC cells and demonstrated the enhanced flexibility of the cells with a 26 mm critical bending radius. Also, we show that the nano-texture Si wafer provide a higher efficiency of 18.68%, whereas the micro-texture one exhibits 18.10%.