Oriented Growth of Al2O3:ZnO Nanolaminates for Use as Electron-Selective Electrodes in Inverted Polymer Solar Cells

Atomic layer deposition is used to synthesize Al ₂O ₃:ZnO(1:x) nanolaminates with the number of deposition cycles, x, ranging from 5 to 30 for evaluation as optically transparent, electron-selective electrodes in polymer-based inverted solar cells. Al ₂O ₃:ZnO(1:20) nanolaminates are found to exhibit the highest values of electrical conductivity (1.2 × 10 ³ S cm ^-1; more than six times higher than for neat ZnO films), while retaining a high optical transmittance (â¥80% in the visible region) and a low work function (4.0 eV). Such attractive performance is attributed to the structure (ZnO crystal size and crystal alignment) and doping level of this intermediate Al ₂O ₃:ZnO film composition. Polymer-based inverted solar cells using poly(3-hexylthiophene) (P3HT):phenyl-C ₆₁-butyric acid methyl ester (PCBM) mixtures in the active layer and Al ₂O ₃:ZnO(1:20) nanolaminates as transparent electron-selective electrodes exhibit a power conversion efficiency of 3% under simulated AM 1.5 G, 100 mW cm ^-2 illumination.