Wide band-gap organic molecules containing benzodithiophene and difluoroquinoxaline derivatives for solar cell applications

• Published in: Molecular Crystals and Liquid Crystals 2019-05, Vol.685 (1), p.29-39
• Main Authors: Agneeswari, Rajalingam, Kong, Minsung, Lee, Jihoon, Kwon, Ji Hyeon, Tamilavan, Vellaiappillai, Park, Seong Soo, Park, Sung Heum, Jin, Youngeup
• Format: Article
• Language: English
• Subjects: benzodithiophene-based molecules; Butyric acid; Chemical synthesis; Electrons; Energy conversion efficiency; Energy gap; Energy levels; Maximum power; Molecular orbitals; Organic chemistry; organic solar cells; Photovoltaic cells; quinoxaline-based molecules; Quinoxalines; small molecule solar cells; Solar cells; Thermal stability; Weight loss; wide band-gap molecules
• ISSN: 1542-1406; 1563-5287; 1527-1943
• DOI: 10.1080/15421406.2019.1645458

Two new semiconducting organic small molecules, namely BDTQ-BDT(EH) and BDTQ-BDT(OC), were prepared by attaching electron accepting 2,3-didodecyl-6,7-difluoro-5,8-di(thiophen-2-yl)quinoxaline (DTQ) unit on 2,6-position of electron donating 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene (BDT(EH)) and 4,8-bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene (BDT(OC)) units. Molecule BDTQ-BDT(EH) showed higher thermal stability (5% weight loss temperature, T d "349 о C), slightly lower band-gap (E g "2.10 eV) and deeper highest occupied molecular orbital energy level (HOMO "-5.36 eV) level compared to those (T d "336 о C, E g "2.11 eV, and HOMO "-5.30 eV, respectively.) of the molecule BDTQ-BDT(OC). The organic solar cells (OSCs) made with the synthesized molecules as an electron donor and [6,6]-phenyl C 71 butyric acid methyl ester (PC 70 BM) as an electron acceptor gave a maximum power conversion efficiency (PCE) of 1.20% and 0.83%, respectively, for BDTQ-BDT(EH) and BDTQ-BDT(OC). This study confirmed that the substituents attached on the 4,8-position of BDT unit greatly alter the properties of the resulting molecules.