Synthesis of nitrogen-doped carbon dots/polymer composites for their application in organic-based solar cells

Abstract

This study reports the synthesis, application and investigation of fluorescence properties of nitrogen-doped carbon dots (NCdots). The NCdots were synthesised using different precursors such as: citric acid (CA) with ethylenediamine (EDA), and fumaronitrile (FN) via microwave-irradiation method. The as-synthesized NCdots from CA with EDA (NCdots-CAEDA) and FN (NCdots-FN) were both spherical in shape and the average sizes were around 3-5 nm. Both types of NCdots demonstrated excellent fluorescence properties with excitation-dependent fluorescence behaviours. The composition of the as-synthesized NCdots was explored by X-ray photoelectron spectroscopy (XPS), showing different amount of carbon, hydrogen, nitrogen and oxygen contents. The most dominant nitrogen configuration in NCdots-CAEDA was pyridinic and in NCdots-FN was pyrrolic nitrogen. The surface functional groups of both types of NCdots were confirmed by fourier transformation infrared microscopy (FTIR). Both types of NCdots were applied in organic solar cells, modifying the active layer. The results demonstrated that the device modified with NCdots-FN outperformed the device modified with NCdots-CAEDA. In order to investigate the fluorescence properties of NCdots, various reaction conditions such as: the amount of EDA, solvent, reaction time and microwave power were varied. The results showed that 1.0 ml EDA, water, 10 min and 500 W were the optimal synthesis conditions for the preparation of the NCdots-CAEDA with good fluorescence properties. The fluorescence properties of NCdots play a crucial role in organic photovoltaics (OPVs). The functional groups on the surface of the NCdots-CAEDA were also removed by annealing the sample at 500 ℃ for 2 h at a heating rate of 10 ℃/min to further investigate the fluorescence properties of NCdots. The fluorescence properties of the NCdots-CAEDA were destroyed after annealing the sample.