Synthesis by direct arylation reaction of photovoltaic D–π–A polymers based on fluorene-thiophene- fragment and fluorinated benzothiadiazole derivatives

Synthesis of three photovoltaic polymers PFBT-HH, PFBT-HF and PFBT-FF based on benzothiadiazole derivatives and fluorene ring was carried out by direct arylation reaction. The polymers were designed to have a donor–π–acceptor –(D–π–A)_n– structure, PFBT derivatives were synthetized employing similar reaction conditions to evaluate the effect of fluorine atoms into the acceptor moiety. For synthesis of PFBT-polymers via direct arylation reaction, the presence of fluorine atoms promotes materials with lower molecular weight and with deep HOMO and LUMO energy levels. An expected increment of photochemical stability with the substitution of fluorine atoms on polymers was observed for its pristine films, and the reduction of polymers photodegradation due to presence of PC₆₁BM fullerene derivative. Photovoltaic characteristics of PFBT-polymers were evaluated into Polymer Solar Cell with bulk- heterojunction architecture fabricated under the configuration glass/ITO/PEDOT:PSS/polymer:PC₆₁BM/PFN/FM. Devices were fabricated at room atmospheric conditions, using an easy-to-manufacture superior electrode (FM = Field’s metal) which was free vacuum deposited by melting it about 90 °C, average power conversion efficiencies of 2.3, 1.1 and 1.2% were reached for high molecular weight fractions of polymers PFBT-HH, PFBT-HF and PFBT-FF, respectively.