Opto(electrical) properties of triphenylamine-based polyazomethine and its blend with [6,6]-phenyl C61 butyric acid methyl ester

Abstract

Polyazomethine (OFBF-TPA) based on triphenylamine (TPA) and octafluorobiphenyl (OFBF) moieties was tested as donor–acceptor (D-A) for bulk heterojunction polymeric solar cells. The temperatures of 5% weight loss ( T5%) of the polyazomethine range from 323 to 328°C, depending on the gas used (air and nitrogen). The conductivity of OFBF-TPA was approximately 10−10 S/cm for not annealed sample and at about 10−6 S/cm for the ones annealed at room temperature, as determined by impedance spectroscopy. Surface of the polymer and mixture polymer–[6,6]-phenyl C61 butyric acid methyl ester (PCBM) was smooth with the Rms value in the range 0.58–1.95 nm as was detected by the atomic force microscopy (AFM) technique. UV-vis spectrum of the mixture OFBF-TPA-PCBM exhibited higher absorption intensity than the UV-vis spectrum of OFBF-TPA lacking PCBM. The thin solid film of OFBF-TPA and OFBF-TPA-PCBM showed one main absorption band with a maximum peak at 414 and 411 nm, respectively. For the mixture OFBF-TPA-PCBM, the second absorption band at 333 nm was found. No influence of annealing on the absorption properties was observed. The polymer solar cell devices were fabricated by spin coating the blend solution of the OFBF-TPA and PCBM and investigated in dark and under an illumination of 100 mW/cm2, with an AM1.5 G. Electrical behavior of the device indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT)- poly(styrenesulfonate) (PSS)/OFBF-TPA-PCBM/Al was tested by impedance spectroscopy in dark and under illumination. For all measured devices, Nyquist plots were presented. The annealing significantly improved the electrical conductivity of the investigated devices. Electrical and photovoltaic properties of OFBF-TPA were compared with the properties of polyazomethine based on TPA and fluorene moieties (F-TPA).