Design and fabrication of silicon nanowires towards efficient solar cells

The recent rise of semiconductor nanowires opens new opportunities for realizing high efficiency photovoltaic devices at low cost due to the unique one-dimensional structure with remarkable electrical and optical properties. Particularly, silicon nanowires (SiNWs), as one of the most earth-abundant materials, have been investigated worldwide to develop cost-effective solar cells. Great efforts have been devoted to fabricating ordered/disordered SiNWs using cost-effective approaches and achieving optimized structural parameters, such as array periodicity, nanowire morphology, length and diameter. Systematic theoretical investigations along with experimental studies on optical and electrical properties of SiNWs have been carried out. These efforts have led to obtaining remarkable improvement of the power conversion efficiency of SiNW solar cells from <1% to >10% in the last few years. However, till now, the power conversion efficiency of these SiNW solar cells is far from satisfactory for any commercial applications compared with the traditional bulk silicon solar cells. Further development of SiNW solar cells requires better understanding of the optical and electrical properties of the nanowire solar cells. Improvement in fabrication of high quality nanowires in a controlled fashion also plays a significant role in nanowire solar cell design and fabrication. To guide future development of SiNW solar cells, the recent work on SiNWs is reviewed. Following that, various techniques aiming to achieve high quality nanowires at low cost are introduced. Both bottom-up and top-down techniques are discussed. Then, electrical properties and various types of solar cells based on SiNWs are discussed. Finally challenges and prospects of SiNW solar cells are presented.