5,10-Dihydroindolo[3,2‑b]indole-Based Copolymers with Alternating Donor and Acceptor Moieties for Organic Photovoltaics

• Published in: Macromolecules Vol. 46; no. 4; pp. 1350 - 1360
• Main Authors: Owczarczyk, Zbyslaw R, Braunecker, Wade A, Garcia, Andres, Larsen, Ross, Nardes, Alexandre M, Kopidakis, Nikos, Ginley, David S, Olson, Dana C
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26-02-2013
• Subjects: Applied sciences; Energy; Exact sciences and technology; Natural energy; Organic polymers; Photovoltaic conversion; Physicochemistry of polymers; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Solar cells. Photoelectrochemical cells; Solar energy; Terpolymer; Stille coupling; Chemical solution; Short circuit currents; Pyrrole derivative copolymer; Electrical properties; Fullerene compounds; Solution polycondensation; Lactam; Thiophene copolymer; Organic solar cells; Experimental study; Fill factor; Absorption spectrum; Open circuit voltage; Electrochemical properties; Electronic structure; Conjugated copolymer; Microwave conductivity; Preparation; Aromatic copolymer; Charge carrier generation; Indole derivative copolymer; Thiophene derivative copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma301987p

A series of new donor–acceptor π-conjugated copolymers incorporating 5,10-dihydroindolo[3,2-b]indole (DINI) as an electron donating unit have been designed, synthesized, and explored in bulk heterojunction solar cells with diketopyrrolopyrrole and thienopyrroledione as the electron accepting units. A significant effect of the size and shape of the pendant alkyl substituents attached to the DINI unit on the optical and electronic properties of the copolymers is described. Our study reveals a good correlation between the theoretical calculations performed on the selected materials and the experimental HOMO, LUMO, absorption spectra, and band gap energies of the corresponding copolymers. The band gaps of the conjugated copolymers can be tailored over 0.4 eV by the electron-withdrawing nature of the different acceptor units to provide better overlap with the solar spectrum, and the energy levels can be tuned ∼0.2 eV depending on the alkyl substituents employed. For the polymers in this study, a nonoptimized power conversion efficiency as high as 3% was observed.