Comparative study of one-pot and facile methods to synthesize codoped CQDs with low band gap and photovoltaic properties

Three different one-pot methods of electrochemical, solvothermal, and pyrolysis were applied for the synthesis of nitrogen-doped carbon quantum dots (N-CQDs), N-F codoped carbon quantum dots (CQDs), and N-S codoped CQDs from monoethanolamine and citric acid precursors. Ammonium fluoride and/or thiourea were used as the precursors of the second dopant corporation. The effective synthesis parameters were studied on the basis of the factorial experimental design methodology to maximize absorption edge and reduce band gap in UV-visible spectroscopy. Among the best results, the synthesized N-F/CQDs prepared from ammonium fluoride and citric acid in monoethanolamine revealed the highest absorption edge of 650 nm, the band gap of 1.91 eV, and the particle size of 24 +/- 7 nm using the pyrolysis method. The X-ray photoelectron spectroscopy (XPS) analysis indicated simultaneous doping of F and N atoms in the CQDs structure, and the photoluminescence (PL) analysis revealed excitation-dependent properties, which are effective for optical sensor and solar cell applications.

Automated summary

In this study, nitrogen-doped carbon quantum dots (N-CQDs), N-F codoped carbon quantum dots (CQDs), and N-S codoped CQDs were synthesized using three different methods, including electrochemical, solvothermal, and pyrolysis, with monoethanolamine and citric acid precursors. Ammonium fluoride and/or thiourea were used as the precursors for the second dopant. Factors affecting the synthesis parameters were examined to optimize the absorption edge and reduce the band gap in UV-visible spectroscopy. The best results were obtained with the pyrolysis method, which yielded N-F/CQDs with the highest absorption edge of 650 nm, a band gap of 1.91 eV, and a particle size of 24 +/- 7 nm. X-ray photoelectron spectroscopy (XPS) analysis confirmed the simultaneous doping of F and N atoms in the CQDs structure, and photoluminescence (PL) analysis revealed excitation-dependent properties suitable for optical sensor and solar cell applications.