Synthesis and characterization of π-bridged [A(DA`nD`)2] based small molecules with potential optoelectronic application

Abstract Alternating different donor units like ethyldioxy-thiophene (ED)/thiophenes (T) and acceptor units isoindigo (ID) /benzothiadiazle (BT) were attached together with the aid of Pd catalyzed C–H activation condition and forming [A(DA`nD`)2] based two π-bridged small molecules, ID(EDBT2TH)2 and ID(EDBT3T)2. Even the new materials have a significant high molecular weight, they are obtained with high yields and are completely soluble in organic solvents which helps the solution processability of organic devices. One of the synthesized small molecules has a terminal alkyl chain and the other is longer in conjugation length by thiophene ring extension. The alternating donor/acceptor units improves the intramolecular charge transfer across the backbone structure. The absorption spectra, electrochemical properties, hole mobility, morphology of the cast films, and photovoltaic performance are investigated considering the different in the terminal group of the synthesized materials, the presence of different donor and acceptor moieties as well as (ED-ID-ED) π-bridge unit. Small molecules under study possess broad absorption with low band gaps which encouraged us to screen the power conversion efficiencies (PCE) of their photovoltaic cells. ID(EDBT2TH)2 and ID(EDBT3T)2 showed 1.4 and 1.3 %, in PCE, respectively, for their first OPV device screening.