The new low‐band gap polymers comprising C‐, Si‐, or N‐bridged dithiophene and alkoxy‐modified 2,1,3‐benzooxadiazole units for bulk heterojunction solar cells

Abstract

In this study, we used Stille coupling polymerization to synthesize a series of new low‐band gap‐conjugated polymers—PCyTBO, PCySiTBO, and PCyNTBO—comprising mainly electron‐rich C‐, Si‐, and N‐bridged dithiophene units in conjugation with electron‐deficient alkoxy‐modified 2,1,3‐benzooxadiazole moieties. The highest occupied molecular orbital energy levels of these polymers become higher as the electron‐donating ability of C‐, Si‐, or N‐bridged dithiophene units increases. These polymers also displayed excellent thermal stability and broad spectral absorptions, with PCySiTBO revealing some crystallinity. As a result, the photovoltaic device incorporating the PCySiTBO/PC71BM (1:1) blend system and 1,8‐diiodooctane (2 vol %) as an additive exhibited excellent performance, under AM 1.5 G irradiation (100 mW cm−2), with a value of Voc of 0.64 V, a short‐circuit current density of 13.8 mA cm−2, a fill factor of 0.57, and a promising power conversion efficiency of 5.0%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

All-Polymer Solar Cells Based on Fully Conjugated Block Copolymers Composed of Poly(3-hexylthiophene) and Poly(naphthalene bisimide) Segments

“…The development of organic solar cells requires donor and acceptor materials that can efficiently facilitate these four fundamental steps. A large variety of donor materials, such as low-band-gap polymers − and poly(3-hexylthiophene) (P3HT)-based rod–coil block copolymers, − have in fact been developed, thereby facilitating significant improvement of the PCEs. On the other hand, acceptor materials are, compared to donor materials, far less developed, and the fullerene derivative [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) is the only conventional acceptor material for organic solar cells .…”

Side Chain Structure Affects the Photovoltaic Performance of Two-Dimensional Conjugated Polymers

“…Scheme outlines our syntheses of the designed polymers. To ensure good solubility of the BO derivative M1 , we positioned two neighboring octyloxy chains on the BO ring as reported in previous studies. − We synthesized M2 , M3 , and M4 using methods reported in the literature. From Stille couplings of M2 , M3 , and M4 with M1 in the presence of Pd 2 dba 3 as the catalyst in CB at 130 °C for 48 h, we obtained the polymers PBDTTBO, PBDTPBO, and PBDTFBO, respectively, in yields of 60–70%.…”

“…Benzothiadiazole (BT) is one of the stronger electron-withdrawing moieties used widely in PSCs due to a combination of its electron accepting properties and its ability to adopt a quinoid structure, resulting in medium-band-gap, coplanar polymers . Benzooxadiazole (BO) is an electron-deficient heterocycle having a structure similar to that of BT, but with a lower-lying oxidation potential, − thereby potentially increasing the V oc of corresponding devices containing its blends with fullerene derivatives. Several reports describe the photovoltaic properties of 4,7-dithiophene-substituted BO-based conjugated polymers, with the highest power conversion efficiency having been 5–7%. − …”

Comprehensive study of pyrido[3,4‐b]pyrazine‐based D–π–a copolymer for efficient polymer solar cells

“…Benzo[1,2‐ b :4,5‐ b ′]‐dithiophene (BDT) is a representative donor block for high‐mobility polymer semiconductors because of its rigidity, coplanarity by fusing a benzene with two flanking thiophene units, high hole mobility, extremely extended π‐conjugation, favorable interchain π–π stacking, and proper side chain patterns for enhanced solubility . In addition, quinoxaline derivatives with two electron‐withdrawing imine nitrogen atoms are of particular interest as electron‐accepting moieties are not only easily modified but also side‐substituted to finely tune the optoelectronic properties of the resulting polymers .…”