All device fabrication steps were performed under CR1000 conditions. Glass slides with patterned ITO (Naranjo, 130-nm thickness, active area) were cleaned in several rinsing steps, including ultrasound treatment with Teepol industrial detergent, deionized water, and isopropanol. The following stack was used as a reference: ZnO nanoparticles were synthesized according to 19 using the hydrothermal condensation of Zn(acetate). After several rinsing steps, the nanoparticles were redispersed in acetone and applied by spin coating (1000, , 60 s). The photoactive layer was spin coated from a 2 wt.%:2 wt.% poly-(3-hexylthiophene) (P3HT, Plextronics, Plexcore Mw ):[6,6] phenyl C61-butyric acid methyl ester (PCBM, 99%, Nano-C) (P3HT:PCBM) solution in chlorobenzene (550, , 95 s). The resulting ZnO and P3HT:PCBM layer thicknesses were approximately 50 and 220 nm, respectively. PEDOT:PSS (PEDOT, Agfa, Orgacon S315) was spin coated at 2000, for 60 s to form a 50-nm thick layer. The devices were annealed at 130°C for 10 min in a atmosphere.