title: Work-Function and Surface Energy Tunable Cyanoacrylic Acid Small-Molecule Derivative Interlayer on Planar ZnO Nanorods for Improved Organic Photovoltaic Performance.
abstract: The issue of work-function and surface energy is fundamental to "decode" the critical inorganic/organic interface in hybrid organic photovoltaics, which influences important photovoltaic events like exciton dissociation, charge transfer, photocurrent (Jsc), open-circuit voltage (Voc), etc. We demonstrate that by incorporating an interlayer of cyanoacrylic acid small molecular layer (SML) on solution-processed, spin-coated, planar ZnO nanorods (P-ZnO NRs), higher photovoltaic (PV) performances were achieved in both inverted organic photovoltaic (iOPV) and hybrid organic photovoltaic (HOPV) devices, where ZnO acts as an "electron-transporting layer" and as an "electron acceptor", respectively. For the tuned range of surface energy from 52.5 to 33 mN/m, the power conversion efficiency (PCE) in bulk heterojunction (BHJ) iOPVs based on poly(3-hexylthiophene) (P3HT) and phenyl-C60-butyric acid methyl ester (PC60BM) increases from 3.16% to 3.68%, and that based on poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2-6-diyl)] (PTB7:Th):[6,6]-phenyl C71butyric acid methyl ester (PC71BM) photoactive BHJ increases from 6.55% to 8.0%, respectively. The improved PV performance in iOPV devices is majorly attributed to enhanced photocurrents achieved as a result of reduced surface energy and greater electron affinity from the covalent attachment of the strong electron-withdrawing cyano moiety, while that in HOPV devices, where PCE increases from 0.21% to 0.79% for SML-modified devices, is ascribed to a large increase in Vocbenefitted due to reduced work function effected from the presence of strong dipole moment in SML that points away from P-ZnO NRs.
authors.affiliation: School of Semiconductor and Chemical Engineering, Chonbuk National University , 664-14, 1-ga Deokjin-dong, Deokjin-gu, Jeonju, Jeonbuk 561-756, Republic of Korea.
authors.forename: Swapnil B
authors.initials: SB
authors.lastname: Ambade
authors.affiliation: School of Semiconductor and Chemical Engineering, Chonbuk National University , 664-14, 1-ga Deokjin-dong, Deokjin-gu, Jeonju, Jeonbuk 561-756, Republic of Korea.
authors.forename: Rohan B
authors.initials: RB
authors.lastname: Ambade
authors.affiliation: School of Semiconductor and Chemical Engineering, Chonbuk National University , 664-14, 1-ga Deokjin-dong, Deokjin-gu, Jeonju, Jeonbuk 561-756, Republic of Korea.
authors.forename: Sushil S
authors.initials: SS
authors.lastname: Bagde
authors.affiliation: School of Semiconductor and Chemical Engineering, Chonbuk National University , 664-14, 1-ga Deokjin-dong, Deokjin-gu, Jeonju, Jeonbuk 561-756, Republic of Korea.
authors.forename: Soo-Hyoung
authors.identifier: http://orcid.org/0000-0002-2730-5723
authors.initials: SH
authors.lastname: Lee
keywords: dipole moment; hybrid organic photovoltaic cell; interfacial modifier; inverted organic photovoltaic cell; planar ZnO nanorods; surface energy; work function