In this paper we report the rationale and implementation of a new building block for organic electronics based on 4,8-di(2-thienyl)-benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) (iso-BBT-T2) and realization of two alkyl-functionalized iso-BBT-tetrathiophene (T4) alternating copolymers (P1 with alkyl = 2DT and P2 with alkyl = 2DH). Compared to the previously investigated small molecules/polymers based on the conventional 4,8-di(2-thienyl)-benzo[l,2-c:4,5-c′]bis[ l,2,5]thiadiazole (BBT-T2), the use of the iso-BBT heterocycle widens the polymer band gap to a region (∼1.4 eV) compatible for use in single junction solar cells. The influence of iso-BBT vs BBT structural variation on the molecular structure, electronic characteristics, and optical properties was accessed by DFT computations, single-crystal determination, optical absorption, and electrochemical measurements. In-plane charge transport for P1 and P2 was investigated in an organic thin-film transistor (OTFT) structure demonstrating hole mobilities approaching 1 cm2 V-1 s-1 and further enhanced by off-center spin-coating method to 1.32 cm2 V-1 s-1. Using PC61BM as acceptor, a remarkable PCE of 10.28% was achieved for P1 along with a current density > 20 mA/cm2. The substantial PCEs of these devices, despite the relatively narrow donor energy gap, is due to retention of high open circuit voltages (Voc > 0.8 V) as the result of the small energy loss (Eloss < 0.6 eV). Atomic force microscopy, transmission electron microscopy, and X-ray diffraction characterization further support the solar cell trends and rationalize structure-property correlations. These results demonstrate that iso-BBT-T2-based polymers are promising candidates for both organic electronics and photonic applications.
|Original language||English (US)|
|Number of pages||11|
|Journal||Chemistry of Materials|
|State||Published - Sep 10 2019|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Materials Chemistry
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CCDC 1955832: Experimental Crystal Structure Determination
Bianchi, L. (Contributor), Zhang, X. (Contributor), Chen, Z. (Contributor), Chen, P. (Contributor), Zhou, X. (Contributor), Tang, Y. (Contributor), Liu, B. (Contributor), Guo, X. (Contributor) & Facchetti, A. F. (Contributor), Cambridge Crystallographic Data Centre, 2019
DOI: 10.5517/ccdc.csd.cc23n6cc, http://www.ccdc.cam.ac.uk/services/structure_request?id=doi:10.5517/ccdc.csd.cc23n6cc&sid=DataCite