Photophysical, electrochemical and photovoltaic properties of thiophene-containing arylene-ethynylene/arylene-vinylene polymers

Abstract This work reports the properties of two types of thiophene-containing poly(arylene-ethynylene)- alt -poly(arylene-vinylene)s polymers, whose repeating units (–Ph–C≡C–Th–CH=CH–Ph–CH=CH–) n , 1 , and (–Th–C≡C–Ph–C≡C–Th–CH=CH–Ph–CH=CH–) n , 2 , consist respectively of a 1 : 2 and a 2 : 2 ratio of –C≡C–/–CH=CH– moieties. Although similar electrochemical data (HOMO: − 5.43 eV, LUMO: ∼− 3.15 eV, E g ec  = 2.28 eV) as well as identical thin film absorption behaviour ( λ a  = 501 nm, E g opt  = 2.10 eV) were obtained for both types of materials, significant differences in their thin film photoluminescence behaviour and photovoltaic properties were observed. While polymer 1 shows a fluorescence maximum at λ e  = 568 nm (with a fluorescence quantum yield of Φ f  = 7%), a total fluorescence quenching was observed in 2 . Solar cells (set up: ITO/PEDOT : PSS/active layer/LiF/Al; active layer consisting of 1 or 2 as donor and PCBM as acceptor in a 1 : 3 ratio by weight) designed from 1 (best cell: V OC  = 900 mV, I SC  = 2.51 mA·cm − 2 , FF = 53.7%, η AM1.5  = 1.21%) show far better photovoltaic performance than those from 2 (best cell: V OC  = 500 mV, I SC  = 1.44 mA·cm − 2 , FF = 37.1%, η AM1.5  = 0.27%).