Photophysics, electronic structure and solar cell performance of a donor-acceptor poly(N-dodecyl-2,7-carbazole-alt-benzothiadiazole) copolymer
Résumé
In this contribution, we investigate the optoelectronic properties of a donor-acceptor poly(N-Dodecyl-2,7-carbazole-alt-benzothiadiazole (CBZ-BT) copolymer in solutions and thin films, by a combination of complementary optical and electronic spectroscopy techniques including stationary absorption and fluorescence, femtosecond time-resolved and ultraviolet/x-ray photoelectron spectroscopy. Absorption spectroscopy revealed two bands at 322/338 and 445/475 nm for CBZ-BT in solutions/films attributed to the carbazole and benzothiadiazole groups respectively. Photoexcitation either to the absorption band of the carbazole or benzothiadiazole group led to a broad and structureless fluorescence spectrum due to large torsional disorder in the excited state, originating from intramolecular energy transfer between carbazole and benzothiadiazole. Time resolved spectroscopy in solutions reveals a transient red-shift of the emission spectrum within less than 5 ps due to exciton migration and/or conformational relaxation of the polymer backbone. In films, this relaxation is faster accompanied by a quenching of the exciton lifetime.
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