YH performed click here the SERS measurements. Both authors read and approved the final manuscript.”
“Background Dye-sensitized solar cells (DSSCs) have shown promising potential as an alternative to Si thin-film solar cells because of low fabrication cost and relatively high efficiency [1, 2]. Efficient utilization of sunlight is greatly

important in photovoltaic systems for high efficiency. Therefore, there have been many studies on the scattering layer to fully utilize incident light inside solar cells by using different morphologies and sizes of scatterers in TiO2-based DSSCs [3–10]. However, few studies for the scattering layer exist in ZnO-based DSSCs [11–13], despite the advantages of

ZnO such as higher carrier mobility and fabrication easiness for various nanostructures [14, 15]. Among various nanostructures, hundred-nanometer-sized PU-H71 nanoporous spheres provide both effective light scattering and large surface area [16]. X. Tao’s group and W. Que’s group have reported on the scattering layer consisting of nanoporous spheres [17, 18]. While they have shown improvements on the scattering effect, large voids between spheres leave the possibility of providing more available surface area where dye can be attached, and better charge transport by improved percolation of large-sized spheres should be achieved. In this paper, we report the improvements of scattering layers using a mixture of nanoparticles and nanoporous spheres. VX-680 Nanoporous spheres act as effective light scatterers with the large surface area, and nanoparticles favor both efficient charge transport and an additional

surface area. Methods The ZnO nanoporous spheres were synthesized by using zinc acetate dihydrate (0.01 M, Zn(CH3COO)2 · 2H2O, Sigma-Aldrich, St. Louis, MO, USA) and diethylene glycol ((HOCH2CH2)2O, Sigma-Aldrich) in an oil bath at 160°C for 6 h [16]. After washing with ethanol, the as-synthesized ZnO nanoporous spheres check (NS) and ZnO nanoparticle (NP) (721085, Sigma-Aldrich) were mixed to the weight ratios of NP to NS of 10:0, 7:3, 5:5, 3:7, and 0:10. To fabricate bilayer-structured electrodes, a paste consisting of only ZnO nanoparticles (NP/NS = 10:0) was first spread on a fluorine-doped tin oxide substrate (FTO, TEC 8, Pilkington, St. Helens, UK) covered with a dense TiO2 blocking layer by sputtering. After solvent evaporation, the mixed pastes with various ratios of NS and NP were spread on top of the nanoparticle film by a doctor blade method. The active area was 0.28 cm2, and the as-deposited films were subsequently annealed at 350°C for 1 h. The films were sensitized with 0.5 mM of N719 dye (RuL2(NCS)2:2TBA, L = 2,2′-bipyridyl-4,4′-dicarboxylic acid, TBA = tetrabutylammonium, Solaronix, Aubonne, Switzerland) for 30 min at RT.