Aqueous Solution Processed, Ultrathin ZnO Film with Low Conversion Temperature as the Electron Transport Layer in the Inverted Polymer Solar Cells

Abstract

Ultrathin ZnO layer of ca. four nm thick deposited from an aqueous zinc oxide hydrate (ZnO·xH2O) solution is developed as the electron transport layer (ETL) in the inverted polymer solar cells (PSCs). Because of the low energy metal–ammine dissociation and hydroxide condensation/dehydration chemistry, a conversion temperature (TA) as low as 80 °C is achieved. With the active layer of poly(N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-3′,2′,1′-benzothiadiazole)) doped with [6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PC71BM), the average power conversion efficiency of the devices is up to 6.48%, and the short circuit current density reaches 11.4 mA cm–2. In comparison, the devices with traditional sol–gel processed ZnO electron transport layer has a power conversion efficiency of 5.53% at an annealing temperature of 200 °C. The device performance improvement is attributed to the better charge transportation and smoother surface of the ZnO film deposited from ZnO·xH2O aqueous solution. ...