Synthesis, electrochromic characterization and solar cell application of thiophene bearing alternating copolymers with azobenzene and coumarin subunits

In this study, azobenzene and coumarin functionalized thiophene comprising two copolymers (poly (4-((3"'-hexyl-[2,2 ':5 ',2 '':5 '',2"'-tetrathiophene] - 3 '-yl)methoxy) - 2H-chromen-2-one (P1) and poly (1-(4-((4"'-hexyl-[2,2 ': 5 ', 2 '': 5 '', 2"' - tetrathiophene] - 3 '-yl) methoxy) phenyl) -2-phenyldiazene) (P2)), were designed and synthesized according to the donor-acceptor (D-A) approach to investigate their electrochemical, optical and photovoltaic behaviors. Among the various copolymerization methods to obtain P1 and P2, Stille copolymerization reaction was preferred. The HOMO and LUMO values were determined via cyclic voltammetry (CV) as -5.64 eV and -3.76 eV for P1 and -5.47 eV and -3.83 eV for P2, respectively. The optical band gaps of the polymers were calculated as 1.88 eV and 1.64 eV using UV-VIS spectrophotometer for P1 and P2. Electrochemical and spectroelectrochemical studies for synthesized copolymers support their usage in organic solar cell applications. The organic solar cells (OSCs) were designed using polymer as an electron donor group and PC60BM as an electron acceptor group. Performances of OSCs based on P1 and P2 were investigated with the device structure of ITO/PEDOT:PSS/Polymer(P1/P2):PC60BM/LiF/Al. The preliminary solar cell results were reported here and studies are going on in our laboratories to increase the efficiency. The highest power conversion efficiency was obtained as 0.81% for P1 based device with 0.47 V open-circuit voltage (V-oc) and 4.92 mA/cm(2) current density (J(sc)) values. The highest efficiency for P2 comprising device was found to be 0.96% under optimum conditions with 0.60 V and 4.98 mA/cm(2), V-oc and J(sc) values, respectively.