Hee Un Kim

Naphthalene-, Anthracene-, and Pyrene-Substituted Fullerene Derivatives as Electron Acceptors in Polymer-based Solar Cells

A series of aryl-substituted fullerene derivatives were prepared in which the aromatic moiety of [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) was modified by replacing the monocyclic phenyl ring with bicyclic naphthalene (NC61BM), tricyclic anthracene (AC61BM), and tetracyclic pyrene (PyC61BM). The PC61BM derivatives were synthesized from C60 using tosylhydrazone and were tested as electron acceptors in poly(3-hexylthiophene) (P3HT)-based organic photovoltaic cells (OPVs). The lowest unoccupied molecular orbital (LUMO) energy level of NC61BM (-3.68 eV) was found to be slightly higher than those of PC61BM (-3.70 eV), AC61BM (-3.75 eV), and PyC61BM (-3.72 eV). The electron mobility values obtained for the P3HT:PC61BM, P3HT:NC61BM, P3HT:AC61BM, and P3HT:PyC61BM blend films were 2.39 × 10(-4), 2.27 × 10(-4), 1.75 × 10(-4), and 2.13 × 10(-4) cm(2) V(-1) s(-1), respectively. P3HT-based bulk-heterojunction (BHJ) solar cells were fabricated using NC61BM, AC61BM, and PyC61BM as electron acceptors, and their performances were compared with that of the device fabricated using PC61BM. The highest power conversion efficiencies (PCEs) observed for devices fabricated with PC61BM, NC61BM, AC61BM, and PyC61BM were 3.80, 4.09, 1.14, and 1.95%, respectively, suggesting NC61BM as a promising electron acceptor for OPVs.

PL Quenching of Poly(3-hexylthiophene) by 2,2′,7,7′-Tetradiphenylamino-9,9′-Bifluorenylidene

2,2′,7,7′-Tetradiphenylamino-9,9′-bifluorenylidene, TDPABF, was synthesized by reductive dimerization using Lawessons reagent. It is soluble in common organic solvents such as dichloromethane, chloroform, and 1,2-dichlorobenzene. Its synthesis was confirmed by 1H-, 13C- NMR, MALDI-TOF, and FT-IR spectroscopy. Its HOMO and LUMO energy levels were –5.33 eV and –2.98 eV, respectively, using photoelectron spectroscopy and UV-Vis absorption spectra. Its fluorescence quenching properties were investigated through a Stern-Volmer quenching experiment. The PL intensity significantly decreased on increasing the concentration of TDPABF in a P3HT chloroform solution. The calculated Stern-Volmer quenching constant was 9.1 × 104 M−1, which is higher than that reported for PC61BM.

Synthesis and Light-Emitting Properties of New Polyfluorene Copolymers Containing 2,3-Diphenylfumaronitrile

A series of polyfluorene copolymers composed of 9,9-dioctylfluorene (DOF) and 2,3-diphenylfumaronitrile (DPFN), poly(DOF-co-DPFN)s, have been synthesized through a palladium (0)-catalyzed Suzuki coupling reaction, and their light-emitting properties have been investigated. The synthesized copolymers were soluble in common organic solvents such as chloroform, toluene, etc and formed a uniform thin film after spin coating. As the contents of 2,3-diphenylfumaronitrile in the copolymers increases, the optical band gaps of the copolymers decreased and HOMO energy levels were also slightly lowered. The absorption and PL emission spectra of the copolymers containing DPFN units shifted to longer wavelength region than those of poly(9,9-dioctylfluorene). Light-emitting devices were fabricated using these polymers as the emissive layers in an ITO/PEDOT:PSS/Polymer/Balq/LiF/Al configuration.