Photophysics, electronic structure and solar cell performance of a donor-acceptor poly(N-dodecyl-2,7-carbazole-alt-benzothiadiazole) copolymer

Abstract

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.

The effect of protonation on the excited state dynamics of pyrimidine chromophores

“…Initially, a femtosecond time resolved upconversion (FU) system, described in details in the past has been used. 65,66 The FU system is based on a Ti:Sapphire femtosecond laser (80 fs pulse duration, 80 MHz repetition frequency, 800 nm) which, after passing through a Second Harmonic Generator (SHG) crystal, is frequency doubled at 400 nm and is used for the excitation of the samples. The excitation power was below J o u r n a l P r e -p r o o f 2 mW while the samples were continuously rotating to avoid thermal effects.…”