Ibraikulov, Olzhas A.Bechara, RonyChavez, PatriciaBulut, IbrahimTastanbekov, DiasLeclerc, NicolasHebraud, AnneHeinrich, BenoîtBerson, SolennLemaitre, NoëllaChochos, Christos L.Lévêque, PatrickHeiser, Thomas2017-12-222017-12-222015-08-01Olzhas A. Ibraikulov, Rony Bechara, Patricia Chavez, Ibrahim Bulut, Dias Tastanbekov, Nicolas Leclerc, Anne Hebraud, Benoît Heinrich, Solenn Berson, Noëlla Lemaitre, Christos L. Chochos, Patrick Lévêque, Thomas Heiser, Using pyridal[2,1,3]thiadiazole as an acceptor unit in a low band-gap copolymer for photovoltaic applications, In Organic Electronics, Volume 23, 2015, Pages 171-17815661199https://www.sciencedirect.com/science/article/pii/S1566119915001858http://nur.nu.edu.kz/handle/123456789/3016Abstract In this report, we explore the optoelectronic properties of a low band-gap copolymer based on the alternation of electron rich (thiophene and thienothiophene units) and electron deficient units (pyridal[2,1,3]thiadiazole (Py)). Initial density functional theory calculations point out the interest of using the Py unit to optimize the polymer frontier orbital energy levels. A high molecular weight (Mn=49kg/mol) solution-processable copolymer, based on Py, thiophene and thienothiophene units, has been synthesized successfully. From cyclic-voltammetry and UV–visible absorption measurements a relatively deep HOMO level (−5.1eV) and an optical band-gap (1.48eV) have been estimated. Charge transport both in horizontal and vertical directions were extracted from field-effect transistors and space charge limited current diodes, respectively, and led to a relatively high in-plane hole mobility in pure polymer films (0.7×10−2cm2V−1s−1). GIWAXS results showed almost identical in-plane lamellar morphologies, with similar average size and orientation of the polymer crystalline domains in both, pure polymer films and polymer:fullerene blends. Also, the gate-voltage dependence of the field-effect mobility revealed that the energy disorder in the polymer domains was not altered by the introduction of fullerenes. The nevertheless significantly higher out-of-plane hole mobility in blends, in comparison to pure polymer films, was attributed to the minor amorphous polymer phase, presumably localized close to the donor/acceptor interface, whose signature was observed by UV–vis absorption. Promising photovoltaic performances could be achieved in a standard device configuration. The corresponding power conversion efficiency of 4.5% is above the value achieved previously with a comparable polymer using benzo [2,1,3]thiadiazole instead of Py as acceptor unit.Polymer solar cellsEnergy disorderCharge transportField-effect mobilitySpace-charge-limited currentMorphologyArticleCopyright © 2015 Elsevier B.V. All rights reserved.