Synthesis of new near infrared absorption polymers based on thiadiazoloquinoxaline and their solar cell applications

Two new alternating copolymers comprising 4,6,7,9-tetra(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 6,6′,12,12′-tetraoctyl-6,12-dihyroindeno[1,2-b]fluorene (PIFDQ) or 9,9-dioctyl-9H-fluorene (PFDQ) were synthesized via Suzuki polymerization reaction. The optical and electrochemical properties of polymers PIFDQ and PFDQ were found to be quite similar, and their absorption bands were extended from 250 nm to 1100 nm in film. The optical band gaps of the polymers were calculated from the onset wavelength of absorption to be 1.19 eV and 1.16 eV, respectively. The energy conversion ability of the synthesized polymers was tested by making single layer BHJ solar cells with the configuration of ITO/PEDOT:PSS/PIFDQ or PFDQ:PC70BM (1:5, wt%)/TiOx/Al. The overall photovoltaic performance of the device based on PIFDQ was found to be 0.27% with a Voc of 0.41 V, a Jsc of 2.39 mA/cm2, and a FF of 28%, while the device made from PFDQ showed power conversion efficiency (PCE) of 0.16% with a Voc of 0.43 V, a Jsc of 1.30 mA/cm2, and a FF of 28%.