Dithienocarbazole- and benzothiadiazole-based donor-acceptor conjugated polymers for bulk heterojunction polymer solar cells

Abstract

Donor-acceptor (D-A)-conjugated polymers P(BT-C1) and P(BT-C2), with dithieno[2,3-b;7,6-b]carbazole (C1) or dithieno [3,2-b;6,7-b]carbazole (C2) as D-unit and benzothiadiazole (BT) as A-unit, were synthesized. The optical bandgaps of the polymers are similar (1.84 and 1.88 eV, respectively). The structures of donor units noticeably influence the energy levels and backbone curvature of the polymers. P(BT-C1) shows a large backbone curvature; its highest occupied molecular orbital (HOMO) energy level is 5.18 eV, whereas P(BT-C2) displays a pseudo-straight backbone and has a HOMO energy level of 5.37 eV. The hole mobilities of the polymers without thermal annealing are 1.9×10 3 and 2.7×10 3 cm 2 V 1 s 1 for P(BT-C1) and P(BT-C2), respectively, as measured by organic thin-film transistors (OTFTs). Polymer solar cells using P(BT-C1) and P(BT-C2) as the donor and phenyl-C 71 -butyric acid methyl ester (PC 71 BM) as the acceptor were fabricated. Power conversion efficiencies (PCEs) of 4.9% and 5.0% were achieved for P(BT-C1) and P(BT-C2), respectively. The devices based on P(BT-C2) exhibited a higher V oc due to the deeper HOMO level of the polymer, which led to a slightly higher PCE. conjugated polymer, dithienocarbazole, benzothiadiazole, polymer solar cells, power conversion efficiency

Organic Donor‐Acceptor Complexes As Potential Semiconducting Materials

“…Later, two new DA conjugated polymers ( 83 a , b ) were reported that were made of dithieno[2,3‐ b ;7,6‐ b ]carbazoles (D) and BT (A) [153] . However, DFT calculations at the B3LYP/6–31+G level confirmed that these two polymers, although having similar optical bandgaps, exhibited a noticeable change in energy levels and backbone curvature, stemming from the presence of differently oriented donor units.…”

Dithienonaphthalene-Based Non-fullerene Acceptors With Different Bandgaps for Organic Solar Cells

“…Organic solar cells (OSCs) have attracted increasing attention over the past decade due to their light-weight, mechanical flexibility, and potential low-cost (Facchetti, 2011 ; Liu et al, 2014 ; Rong et al, 2015 ). Bulk heterojunction (BHJ) OSCs featuring with an active layer of an electron acceptor material blended with an electron donor material, are widely used (Wu et al, 2011 ; Chen et al, 2013 ; Wang et al, 2014 ; Xu et al, 2015 ).…”