Theoretical, spectroscopical, and experimental investigations of small azomethine molecules for organic solar cells

Abstract

Small azomethine molecules ( 4,4′-bis((2-hydroxy-4-octyloxyphenyl)methylimino)diphenylmethane (BP-DPM) and 4,4′-bis((2-hydroxy-4-octyloxyphenyl)methylimino)diphenyl ether (BP-DPE)) for photovoltaic applications were synthesized by condensation of appropriate arylaldehydes and arylendiamines and characterized using Fourier-transform infrared spectroscopy, 1H NMR, 13C NMR, and liquid chromatography–mass spectrometry. Azomethine molecules are additives in organic solar cells. The effect of a possible energy transfer between BP-DPE and P3HT on the photovoltaic performance of devices employing ternary blends of BP-DPE:P3HT: phenyl-C61-butyric acid methyl ester (PCBM) was investigated by absorption and emission spectra. The devices employing BP-DPE:P3HT:PCBM with 1:4 ratio exhibited a Jsc of 4.2 mA cm−2, Voc of 575 mV, and FF of 0.27 which led to a power conversion efficiency (PCE) of 0.65%. In addition, density functional theory calculations (DFT/B3LYP/6-31G(d)) were used to determine the optimized molecular geometry, highest occupied molecular orbital–lowest unoccupied molecular orbital energies, electronic structures, and the molecular electrostatic potential surfaces of the molecules.