Synthesis and photovoltaic properties of heteroaromatic low-band gap oligomers for bulk heterojunction solar cells

Two new low band gap oligomers, TPyTDzQ-P1 and TPyTDzQ-P2, comprised of electron rich 1-(2,6-diisopropylphenyl)-2,5-di(2-thienyl)pyrrole or 1-(p-octylphenyl)-2,5-di(2-thienyl)pyrrole (TPyT) and electron deficient 6,7-di-2-methylpropane-4,9-bis-(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline (DzQ) units were synthesized using the Suzuki polycondensation reaction. The oligomers were found to harvest the solar flux from the ultraviolet (300 nm) to near infrared (1200 nm) regions. The optical bad gaps of the two oligomers were calculated to be 1.08 eV and 1.10 eV, respectively, while the electrochemical band gaps were calculated to be 1.17 eV and 1.19 eV, respectively. The two oligomers were used as electron donor materials in bulk heterojunction (BHJ) solar cells. The solution processable bulk heterojunction solar cells with ITO/PEDOT:PSS/TPyTDzQ-P1 or TPyTDzQ-P2:PC70BM/TiOx/Al configuration showed a maximum power conversion efficiency (PCE) of 0.43% with a short-circuit current density (Jsc) of 3.41 mA/cm2, open-circuit voltage (Voc) of 0.39 V and fill factor (FF) of 32%.

Heteroaromatic low-band gap oligomers utilizing electron rich thiophene-pyrrol-thiophene unit and electron deficient bis-thiophenyl-thiadiazoloquinoxaline unit were prepared and applied to bulk heterojunction solar cells.Figure optionsDownload as PowerPoint slideHighlights
► Two heteroaromatic low-band gap oligomers were prepared.
► The absorption of the oligomers was in the range of 300–1200 nm in film.
► The optical bad gaps of the oligomers were 1.08 eV and 1.10 eV, respectively.
► The oligomers were applied to bulk heterojunction solar cells.