All cleaned substrates were treated with UV Ozone treatment for 15 min. Figure 1 Detailed values extracted from the UPS spectra and schematic diagram of organic solar cells. (a) Evolution of secondary electron edge of ITO and ITO/ZnOCs2CO3 and (b) energy level alignment of all materials used in this study. The solution for electron selective layer was prepared by mixing ZnO and Cs2CO3 with different blend ratios, namely, 1:1, 1:2, 1:3, 2:1, and 3:1. The solution-processed ZnO or ZnO:Cs2CO3 was GSK1210151A cell line spin-coated at 1,000 rpm for 25 s onto the cleaned substrates and later annealed at 300°C for 10 min. The photoactive layer either P3HT:PCBM or P3HT:ICBA dissolved in 1,2-dichlorobenzene

was spin-coated at 700 rpm for 25 s and subsequently annealed at 130°C for 30 min or 150°C for 10 min, respectively. GSK2118436 Later, PEDOT:PSS was spin-coated at 4,000 rpm for 25 s onto the photoactive layer and annealed at 120°C for 20 min. To complete the device, 100-nm thick of Al was thermally Selleckchem MK-0518 evaporated at rates 4 A/s through a shadow mask at a base pressure of 10−7 Torr. The active area of the complete devices is 0.04 cm2. To ensure the reproducibility of our results,

we have fabricated 83 devices throughout this work. The following are the fabricated devices based on different photoactive materials. P3HT:PCBM-based devices. Device A-ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Al Device B-ITO/ZnO:Cs2CO3/P3HT:PCBM/PEDOT:2PSS/Al P3HT:ICBA-based devices. Device C-ITO/ZnO/P3HT:ICBA/PEDOT:PSS/Al Device D-ITO/ZnO:Cs2CO3/P3HT:ICBA/PEDOT:PSS/Al Thin film and device characterizations The J-V characteristics of the conventional solar cells were measured using the Keithley 2400 source meter under a solar simulator (AM1.5) with an irradiation intensity of 100 mW/cm2. The EQE measurements were performed using an EQE system (Model 74000) obtained from Newport Oriel Instruments, Irvine, CA, USA, and the HAMAMATSU calibrated silicon cell photodiode (HAMAMATSU, Shizuoka, Japan) was used as the Rebamipide reference diode. The wavelength was controlled with a monochromator to range from 200 to 1,600 nm. AFM imaging

was achieved in air using a Digital Instrument Multimode that is equipped with a nanoscope IIIa controller. XPS measurements were performed in a PHI 5000 VersaProbe (Ulvac-PHI, Chigasaki, Kanagawa, Japan) with background pressure of 6.7 × 10−8 Pa, using a monochromatized Al Kα (hv = 1,486.6 eV) anode (25 W, 15 kV). Ultraviolet photoemission spectroscopy (UPS) measurements were carried out using the He 1 photon line (hv = 21.22 eV) of a He discharge lamp under UHV conditions (4 × 10−10 mbar). The transmittances of ZnO, and ZnO:Cs2CO3 coated on ITO-glass substrates were recorded at room temperature with a SCINCO S4100 (SCINCO, Seoul, South Korea) spectrophotometer. XRD measurements were carried out using X’PERT PRO of PANalytical Diffractometer (PANalytical, Seongnam City, South Korea) with a Cu Kα source (wavelength of 1.