Investigation of optical and electrical properties of new aromatic polyazomethine with thiophene and cardo moieties toward application in organic solar cells

Abstract New polyazomethine (25Th-cardo) based on thiophene and cardo moieties was synthesized, characterized and tested as active layer in solar cells. The structure of polymer was characterized by means of FTIR and 1 H NMR spectroscopy. The temperatures of 5% weight loss of the polyazomethine range from 435 to 455 °C in nitrogen, depending on the heating rate applied. 25Th-cardo has electrochemical energy band gap of approximately ∼1.85 eV, and HOMO energy level at −5.21 eV. Optical absorption properties of pure 25Th-cardo and of its mixtures with [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) were investigated on different substrates: glass or glass/PEDOT:PSS. Electrical properties of the two kinds of devices: ITO/25Th-cardo:PCBM/Al and ITO/PEDOT:PSS/25Th-cardo:PCBM/Al were tested by impedance spectroscopy. The investigated polymer solar cells contained different amounts of PCBM. Bulk heterojunction solar cells with the architecture ITO/PEDOT:PSS/25Th-cardo:PCBM/Al gave a power conversion efficiency 3.5 times higher for the mixture of 25Th-cardo to PCBM 1:2 (w/w) than for 1:1 (w/w) under 100 mW/cm 2 AM1.5G sunlight illumination in air. The external quantum efficiency value of 25Th-cardo:PCBM solar cell was the highest (about 0.3%) in the near UV range from 3.1 to 3.7 eV.