Efficient inverted polymer solar cells using low-temperature zinc oxide interlayer processed from aqueous solution

In this work, an aqueous solution method that entails processing at low temperatures is utilized to deposit a ZnO interlayer in poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C-61 butyric acid methyl ester-based inverted polymer solar cells (PSCs). The effect of ZnO annealing temperature from 50 to 150 degrees C on PSC performance is systemically studied and it is found that the transition point is approximately 80 degrees C. When the ZnO annealing temperature is higher than 80 degrees C, PSCs show similar current density-voltage (J-V) characteristics and achieve a power conversion efficiency higher than 3.5%. Transmittance spectrum, PL spectrum, and surface morphology studies show that an annealing temperature above 80 degrees C is sufficient for ZnO to achieve a relatively good quality, and that a higher temperature only slightly improves ZnO quality, which is confirmed from statistical results. Furthermore, flexible PSCs based on PET substrates show a comparable power conversion efficiency and good flexibility. (c) 2015 The Japan Society of Applied Physics