In order to modulate the optoelectronic properties of thiophene-based conjugated polymers

two novel conjugated polymers ( P1 and P2 ) comprising dithieno[3

2-b:2'

3'-d]phosphole oxides (DTPhos) and 2

2'-bithiophene have been designed and synthesized by Stille polycondensation

and their thermal

electrochemical and photophysical properties were studied.Both polymers are thermally stable with decomposition temperature above 400℃

and exhibit the absorption maxima of ca. 590 nm and the optical band gap of 1.76 eV.The incorporation of DTPhos units into polythiophene backbone results in a 0.15 eV reduction of optical bandgap.HOMO and LUMO energy levels of the polymers as measured by cyclic voltammetry are -5.1 and -2.9 eV

respectively.Thin-film transistors (TFT) and bulk heterojunction solar cells (BHJ-SC) were fabricated based on P1 and P2 .The performance of the devices increased with an increase of the alkyl chain length in the DTPhos units.With a bottom gate and top contact TFT device structure

P2 exhibited the hole mobility up to 0.0077 cm2V-1s-1.Under AM 1.5 G illumination (100 mW/cm2)

BHJ-SC based on P2 displayed an open-circuit voltage of 0.68 V

a short-circuit current of 7.9 mA/cm2

a fill factor of 52% and a power conversion efficiency of 2.8%.These results imply that DTPhos unit is a potential building block for high-performance polymer semiconductors.