Acid-functionalized fullerenes used as interfacial layer materials in inverted polymer solar cells

다국어 초록 (Multilingual Abstract)

Two types of carboxylic acid functionalized fullerence derivatives, 4-(2-ethylhexyloxy)-[6,6]-phenyl C<SUB>61</SUB>-butyric acid (p-EHO-PCBA) and bis-4-(2-ethylhexyloxy)-[6,6]-phenyl C<SUB>61</SUB>-butyric acid (bis-p-EHO-PCBA), were synthesized and investigated as an interfacial layer for inverted polymer solar cells (iPSCs). The -COOH groups on the PCBAs chemisorb to inorganic metal oxide (TiO<SUB>X</SUB>), generating fullerene-based self-assembled monolayers (FSAMs). The devices with the mono- and bis-FSAMs exhibited substantially lower series resistance (R<SUB>S</SUB>) values of 2.10Ωcm<SUP>2</SUP> and 1.46Ωcm<SUP>2</SUP>, compared to that (4.15Ωcm<SUP>2</SUP>) of the unmodified device. The TiO<SUB>X</SUB> films modified with mono- and bis-FSAMs showed higher contact angles of 50<SUP>o</SUP> and 91<SUP>o</SUP>, respectively, than that of the pristine TiO<SUB>X</SUB> film (33<SUP>o</SUP>). The increased contact angles were attributed to the enhanced hydrophobicity, improving the wetting properties with the organic photoactive layer. In addition, a comparison of device characteristics with electroactive FSAMs and non-electroactive benzoic acid SAMs clearly indicates that the FSAMs may suggest an additional pathway for photo-induced charge transfer and charge collection to ITO. After surface modification with FSAMs, the short-circuit current density (J<SUB>SC</SUB>) and fill factor (FF) values increased substantially. The iPSCs based on poly(5,6-bis(octyloxy)-4-(thiophen-2-l)benzo[c][1,2,5]thiadiazole) (PTBT) and [6,6]phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PCBM) as an active layer showed remarkably improved power conversion efficiency up to 5.13% through incorporation of the FSAMs-based interfacial layer.