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Investigation of Optical and Dielectric Constants of Benzobis(thiazole)- based Copolymer Films



Copolymer PBB-T with benzo[1,2-d:4,5-d']bis(thiazole) (BBT) as the
accepting unit and benzodithiophene (BDT) as the donor unit is a promising candidate for highperformance
non-fullerene polymer solar cells (PSCs). So far optical and dielectric constants of the
PBB-T are not fully known.


 PBB-T was synthesized and thin films of PBB-T were prepared. By using the Kramers-Kronig
relations and the transmission spectra of the PBB-T films, the optical and dielectric constants, including
in absorption coefficient (α(λ)), extinction coefficient (κ(λ)), refractive index (n(λ)), dielectric constant
(ε1(λ),ε2(λ)), band gap (Eg) and mobility of the PBB-T films were calculated and analyzed.


At 500 nm, α, κ, n, ε1 and ε2 are 1.65×105 cm-1, 0.46, 1.8163, 3.0 and 1.65 respectively.
Eg is 2.111 eV. The hole mobility of PBB-T are 2.41×10-5 cm2 V-1 s-1 and 1.71×10-4 cm2 V-1 s-1 for
the as-cast film and for the solvent vapor annealed film respectively. The results show that these
optical and dielectric constants of the PBB-T films are almost independent on the thicknesses of
the films, indicating our results are reliable. The features of the optical and dielectric constants
show the PBB-T films are very promising candidates for high-performance non-fullerene PSCs
and potential cut-off filter only permitting red and near-infrared light passing.


 These results are significant for designing optoelectronic devices related to the PBBT
thin films.