ABSTRACT
Wire-like nano-and microstructures are increasingly of great interest for photovoltaics. This geometry provides several distinct advantages for PV that may in the future lead to low-cost, high-efficiency modules. For example, it has been shown that nanowire/tube arrays possess excellent antireflective and light-trapping/absorption properties compared to planar thin-film or bulk materials (Tsakalakos et al. 2007a; Xi et al. 2007). Nanowires/tubes also provide a direct path for transport of minority and majority charge carriers, hence providing the potential to minimize losses associated with surface/interface recombination (Haraguchi et al. 1992; Chung et al. 2000). Doping of nanowires can be controlled during their synthesis (Cui et al. 2000), and both homojunctions and heterojunctions have been shown (Haraguchi et al. 1992; Peng et al. 2004; Dick et al. 2007; Paladugu et al. 2008). Regarding nanowire synthesis, it is indeed possible to grow nanowire arrays over large areas using well-established, scalable processes such as chemical vapor deposition (including plasma enhanced and metal-organic based), wet etching, and solution-based chemical synthesis. The above features make (quasi-) one-dimensional nanostructures such as nanorods, wires, and tubes particularly attractive for photovoltaics. The elongated geometry also allows the nanorod/tube structures to be dispersed in an interpenetrating network such that they may be used as transparent conducting layers. These applications of nanorods (NRs), nanowires (NWs), and nanotubes (NTs) will be explored in more detail below.
