Triphenylamine Based Random Copolymers: The Effect of Molecular Weight on Performance of Solar Cell and Optoelectronic Properties

Two low band gap triphenylamine based random copolymers are synthesized via Pd-catalyzed Stille polycondensation reaction to investigate the role of molecular weight on device performance and optoelectronic properties. 1H NMR spectroscopy, UV−vis absorption spectroscopy, cyclic voltammetry, and gel permeation chromatography (GPC) are used for characterization of polymers. The polymerization conditions are optimized to achieve high molecular weight polymers with enhanced optoelectronic properties. PBTP1 reveals broad absorption in the wavelength range of 300–670 nm whereas PBTP2 has absorption in the wavelength range of 300–660 nm. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are calculated as −5.43 and −3.20 eV for PBTP1 and −5.33 and −3.02 eV for PBTP2. The photovoltaic device containing donor PBTP1 and acceptor PCBM[70] in 1:3 weight ratio reveals the highest power conversion efficiency of 2.27%, with Voc of 0.63 V, Jsc of 8.19 mA cm−2, and fill factor of 44% under illumination of AM 1.5 G, 100 mW cm−2. Organic photovoltaics (OPV) cells fabricated with PBTP2 demonstrate improved photovoltaic results due to higher molecular weight and enhanced optoelectronic properties. Photon-to-current efficiency of 3.65% with a current density of 14.73 mA cm−2, Voc of 0.69 V, and fill factor of 36% are obtained.