Synthesis of Poly(benzothiadiazole-co-dithienobenzodithiophenes) and Effect of Thiophene Insertion for High-Performance Polymer Solar Cells

• Published in: Chemistry : a European journal 2013-09, Vol.19 (39), p.13242-13248
• Main Authors: Yun, Hui-Jun, Lee, Yun-Ji, Yoo, Seung-Jin, Chung, Dae Sung, Kim, Yun-Hi, Kwon, Soon-Ki
• Format: Article
• Language: English
• Subjects: Chemistry; copolymerization; Copolymers; Derivatives; donor-acceptor systems; Electron mobility; Energy conversion efficiency; Photovoltaic cells; photovoltaic systems; semiconductors; Solar cells; Solar energy; Synthesis; thin films; Thiophenes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300445

We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm2 V−1 s−1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model. Excellent charge transport: Novel donor–acceptor conjugated polymers with dithienobenzodithiophenes as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor can be used for high‐performance organic photovoltaics. The high charge‐carrier mobility of copolymer 1 (0.55 cm2 V−1 s−1) and its outstanding charge‐transport characteristics lead to organic solar cells with a power conversion efficiency (PCE) of 5.1 % (see figure).