Abstract
Three conjugated polymers, in which the electron-donating (D) 5-alkylthiophene-2-yl-substitued benzodithiophene was linked to three different electron-accepting (A) moieties, i.e., benzothiadiazole (BT), diphenylquinoxaline (DPQ), and dibenzophenazine (DBP) derivative via thiophene bridge, were synthesized using the Stille coupling reaction. In particular, the strong electron-withdrawing cyano (CN) group was incorporated into the A units BT, DPQ, and DBP to afford three D–A type target polymers PB–BTCN, PB–DPQCN, and PB–DBPCN, respectively. Owing to the significant contribution of the CN-substituent, these polymers exhibit not only low-lying energy levels of both the highest occupied molecular orbital and the lowest unoccupied molecular orbital, but also reduced bandgaps. Furthermore, to investigate the photovoltaic properties of polymers, inverted-type devices with the structure of ITO/ZnO/Polymer:PC71BM/MoO3/Ag were fabricated and analyzed. All the polymer solar cells based on the three cyano-substituted conjugated polymers showed high open-circuit voltages (Voc) greater than 0.89 V, and the highest power conversion efficiency of 4.59% was obtained from the device based on PB-BtCN with a Voc of 0.93 V, short-circuit current of 7.36 mA cm−2, and fill factor of 67.1%.
Highlights
In the past few decades, polymer solar cells (PSCs) have attracted significant interest as a promising clean and renewable energy resource, owing to their advantages, such as high flexibility, facile processability, and cost-effectiveness [1,2,3,4]
Synthesis and Thermal Properties compound 1 and tributylchlorostannane were reacted in the presence of n-butyllithium to produce compound 2
The root-mean-square (RMS) values of the films based on PB–BtCN, PB–DPQCN, and PB–DBPCN are 2.72, 2.50, and 6.88 nm, respectively
Summary
In the past few decades, polymer solar cells (PSCs) have attracted significant interest as a promising clean and renewable energy resource, owing to their advantages, such as high flexibility, facile processability, and cost-effectiveness [1,2,3,4]. The alternating donor-acceptor (D–A) type copolymers between electron-donating and electron-accepting building blocks are used for PSCs, because this configuration can reduce the band gap of polymers significantly through the facile formation of the intramolecular charge transfer (ICT) state [13]. Upon addition strong electron-withdrawing withdrawing groups, the energy levels of. Three CN-substituted electron-accepting moieties, i.e., BT, possessing oneaCN group via a thiophene bridge. CN-substituted strong electron-accepting diphenylquinoxaline (DPQ), and dibenzophenazine (DBP), were used as building blocks the three moieties, i.e., BT, diphenylquinoxaline (DBP), were used for as building target polymers. Owing to the blocks for the three target polymers PB–BtCN, PB–DPQCN, and PB–DBPCN, respectively Owing to the significant contributions of diverse electron-accepting moieties, discernible optical electrochemical properties were measured from photovoltaic and electrochemical properties were measured fromthese thesepolymers.
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