CL participated in the design and preparation, analyzed the results, and helped draft the manuscript. ZL and ZZ participated in the design and coordination of the study. All authors read and approved the final manuscript.”
“Background Solar cells have attracted considerable attention buy BAY 80-6946 because of their potential application in low-cost and flexible energy generation devices. Since the seminal work pioneered by O’Regan and Grätzel

in 1991, dye-sensitized solar cells have been investigated extensively all over the world [1–11]. Assembly of branched nanostructures also received intense scrutiny due to their potential effects to a number of promising applications such as solar cells, water splitting, optoelectronics, sensing, field emission, and more [12, 13]. In 2013, Roh et al. studied solar cells based on nano-branched TiO2 nanotubes, specifically, nanotubes characterized by increased surface area [14]. The results were attractive; they were able to achieve an impressive light-to-electricity conversion rate. Also of note, Roh et al. used organic dye as a sensitizer to fabricate solar devices. However, the use of dye as a sensitizer is problematic for two reasons: first, organic dye is expensive; second, and perhaps more importantly, the organic

dye proved to be unstable. As a result, using dye to sensitize solar cells is still not feasible for practical applications. Because it is critical to tailor materials to be not only cost-effective but also long-lasting, inorganic

semiconductors GSK126 such as CdSe [15, 16], PbS [17–19], CdS [20], and Sb2S3[21, 22] have several advantages over conventional dyes: first, the band gap of semiconductor nanoparticles can be tuned by size to match the solar spectrum; second, their large intrinsic dipole moments can lead to rapid charge separation and a large extinction coefficient, which is known to reduce the dark current and increase the overall efficiency; third, and Carnitine palmitoyltransferase II finally, semiconductor sensitizers provide new chances to utilize hot electrons to generate multiple charge carriers with a single photon. Hence, nano-sized, narrow band gap semiconductors are ideal candidates for the optimization of solar cells to achieve improved performance. To date, CdS-sensitized solar cells have been studied by many groups [23–26]. In most reported works, CdS quantum dots were grown on TiO2 nanotubes and TiO2 nanoporous photoanodes with hierarchical pore distribution. However, little work has been carried out on utilizing nano-branched TiO2 arrays as photoanodes. Compared to polycrystal TiO2 nanostructures, such as nanotubes and nanoparticles, nano-branched TiO2 nanorod arrays, which are grown directly on transparent conductive oxide electrodes, increase the photocurrent efficiency by avoiding the particle-to-particle hopping that occurs in polycrystalline films.