Self-assembled oleamide layer applied for cathode buffer layer of bulk heterojunction solar cells based on PTB7:PC71BM

Abstract

In this work, bulk heterojunction solar cells based on poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl]] and phenyl-C71-butyric-acid-methyl-ester were fabricated using 1,2-dichlolobenzene solutions containing different weight ratios of oleamide. The oleamide layers were self-assembled on the active layer surfaces during the solidification of the active layer after spin coating. A significant increase in open-circuit voltage was observed after the introduction of oleamide at the expense of short-circuit current density. The optimal performance of the solar cell was obtained by spin coating the active layer at 1000 rpm for 60 s using a 1,2-dichlolobenzene solution containing 3% oleamide. The solar cell exhibited a short-circuit current density, an open circuit voltage, a fill factor, and a power conversion efficiency of 13.95 mA/cm2, 0.79 V, 0.47, and 5.22%, respectively. These solar cell behaviors are discussed on the basis of results of morphological analysis by optical microscopy, atomic force microscopy, and surface energy analysis.