Modulation of electronic properties of π‐conjugated copolymers derived from naphtho[1,2‐b:5,6‐b′]dithiophene donor unit: A structure‐property relationship study

Abstract

A set of three donor‐acceptor conjugated (D‐A) copolymers were designed and synthesized via Stille cross‐coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2‐b:5,6‐b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT‐BT, PTNDTT‐BTz, and PTNDTT‐DPP polymers incorporated naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) as the donor and 2,2′‐bithiazole (BTz), benzo[1,2,5]thiadiazole (BT), and pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione (DPP), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X‐ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between −5.14 to −5.26 eV and −3.13 to −3.5 eV, respectively. The spin‐coated polymer thin film exhibited p‐channel field‐effect transistor properties with hole mobilities of 2.73 × 10−3 to 7.9 × 10−5 cm2 V−1 s−1. Initial bulk‐heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]‐phenyl C71 butyric acid methyl ester (PC71BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958

Bithiazole: An Intriguing Electron‐Deficient Building for Plastic Electronic Applications

“…Following the successful synthesis of small molecules M11 and M12 , Lee and co‐workers turned their attention to expanding the scope of their studies, by synthesizing the D–A conjugated copolymer P49 via Stille cross‐coupling reaction . The resulting polymer showed a narrow absorption in the range of 350–650 nm and had an optical bandgap of 1.98 eV.…”

Naphthodithiophenes: Emerging Building Blocks for Organic Electronics

“…NDT3‐based polymers with various A units were synthesized and examined as p‐type semiconducting polymers (Figure ). Among the polymers consisting of the unsubstituted NDT3 unit, e.g., P4 – P12 , except for P4 and P5 , the performances of the OPVs were not very high (PCE < 2.0%, Table ). On the other hand, very high mobility (1.32 cm 2 V −1 s −1 ) in OFETs was achieved for P6 with the DPP unit .…”

“…In particular, P5 presents its versatility as a high‐performance p‐type semiconducting material; P5 ‐based OFETs showed hole mobility as high as 0.54 cm 2 V −1 s −1 , and its BHJ solar cells with PC 61 BM afforded a PCE close to 5% (Table ). These superior characteristics demonstrated by the early NDT‐based D–A polymers prompted researchers to develop new analogues with different A units, such as thieno[3,4‐ b ]thiophene (TT), 2,5‐dihydropyrrolo[3,4‐ c ]pyrrole‐1,4‐dione (diketopyrrolopyrrole, DPP), TzTz, quinoxaline (QX), and benzo[ c ][1,2,5]oxadiazole (BOz) (Figure ) …”

Medium‐Bandgap Conjugated Polymer Donors for Organic Photovoltaics

“…P162 exhibited good solubility and high thermal stability. The OPVS based on the blend of P162 and PC 71 BM showed a PCE of 1.62%, with a V OC of 0.63 V . A summary of chemical structures and device parameters discussed in this section can be found in Figure and Table 11 , respectively.…”