Modulation of optical and electronic properties of quinoxailine-based conjugated polymers for organic photovoltaic cells

Abstract

The synthesis of donor-acceptor type semiconducting copolymers is described. Quinoxaline (QX) or difluorinated quinoxaline (DFQX) derivatives serve as electron acceptors, while thiophene (T) or selenophene (Se) serve as electron donors. Alternating polymers are synthesized through Stille cross-coupling, and their thermal stability, optical and electrochemical properties, field-effect carrier mobilities, film crystallinities, and photovoltaic performances are investigated. The intramolecular charge transfer between the electron-donating and electron-accepting units in the backbone induces absorption from 450 to 750 nm. The optical band-gap energies of the polymers are between 1.65 and 1.73 eV, and depend on the polymer structure. Organic photovoltaic cells fabricated using a polymer composed of DFQX and selenophene (PSe-DFQX) exhibit a power conversion efficiency of 5.14% with an open-circuit voltage of 0.78 V, a short-circuit current density of 11.71 mA/cm(2), and fill factor of 0.57 under AM 1.5 G irradiation (100 mW cm(-2)).