ITO-free inverted organic solar cells fabricated with transparent and low resistance ZnO/Ag/ZnO multilayer electrode

Inverted organic solar cells (OSCs) based on poly (3-hexylthiophene) (P3HT):[ 6,6]-phenyl-C61 butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ) were fabricated with optimized ZnO/Ag/ZnO multilayer and conventional indium-tin oxide (ITO) cathode electrodes and their performance was compared. The ZnO/Ag/ZnO multilayer films showed sheet resistances in the range 3.6-3.9 Omega/sq, while ITO exhibited 14.2 Omega/sq. On the one hand, the carrier concentration gradually decreased from 1.74 x 10(22) to 4.33 x 10(21) cm(-3) as the ZnO thickness increased from 8 to 80 nm, respectively. The transmittance of the ZnO(40 nm)/Ag(19 nm)/ZnO(40 nm) films was similar to 95% at 550 nm, which is comparable to that of ITO (similar to 96%). The multilayer films were smooth with a root mean square (RMS) roughness of 0.81 nm. OSCs fabricated with the ZnO(40 nm)/Ag(19 nm)/ZnO(40 nm) film showed a power conversion efficiency (2.63%) comparable to that of OSCs with a conventional ITO cathode (2.71%). (C) 2015 Elsevier B.V. All rights reserved.