Optoelectronic and Electrochemical Properties of Quantum Confined MoSe2 Grafted Graphene Nano Sheets for Energy Applications

Abstract

Next generation energy devices (batteries, super capacitors, solar cells, and LEDs) call for designing new and novel materials. Molybdenum Diselenide (MoSe2) has superior optoelectronic features among transition metal chalcogenides with high electrical conductivity and tunable size and band gap. The MoSe2/ graphene hybrids have been widely studied for Super capacitors, batteries applications but quantum confined MoSe2 Nano crystals embedded in graphene matrix have not been investigated for thin films solar cells, LEDs, and Super capacitor/batteries applications. This work explores the optoelectronic and electrochemical properties of quantum confined MoSe2 grafted graphene nanosheets for energy applications. The MoSe2 and graphene oxide were synthesized using hydrothermal and improved Hummer’s method, respectively. The CTAB concentration was varied (0.03g, 0.06g, 0.09g, 0.12g) during the hydrothermal process to control the particle size and tune the band gap of the material. The results of the Raman and photoluminescence spectroscopy, UV-Vis. spectroscopy, and CV voltammograms showed that the particle size and band gap energy can be controlled by changing the CTAB concentration. The sample with 0.06g CTAB showed the highest energy density, power density, and specific capacitance, exhibiting a battery-like charge storage mechanism and significant redox activity. The Raman Analysis of MoSe2 samples showed that by varying CTAB concentrations revealed the presence of various vibrational modes. The peaks in the spectra can be attributed to the in-plane vibration of E1g and B12g modes, as well as the J1 and J2 modes. The formation of 1T-MoSe2 and 2H-MoSe2 phases were observed in the samples, with MoSe2-(0.12g CTAB) showing dominant peaks of the 2H phase. The peaks above 450cm-1 were due to the formation of α-MoO3. The photoluminescence spectroscopy (PL) of MoSe2-GO and CTAB samples showed visible luminescence range in all samples. The PL intensity was found to be related to the recombination mechanism of photo-generated electron-hole pairs. MoSe2-GO (0.12g CTAB) showed high recombination which could be due to the CTAB capping agent covering the defect states, leading to non-radiative recombination and PL quenching. MoSe2-GO (0.06g CTAB) showed the lowest PL intensity, likely due to the highest charge separation efficiency. UV-Vis spectroscopy showed that the band gap of MoSe2 increased with increasing CTAB concentration, indicating quantum confinement in MoSe2 Nano sheets. The estimated band gaps were 1.66eV, 2.02eV, 2.37eV, and 2.64eV in MoSe2 (0.03g CTAB), MoSe2 (0.06g CTAB), MoSe2 (0.09g CTAB), MoSe2 (0.12g CTAB) respectively. The absorption spectra of MoSe2-GO composites showed a characteristic absorption peak of GO at 261nm, 274nm, 276nm, and 275.8nm and a broad absorption region assigned to MoSe2 nanosheets decorated on the GO network. The CV voltammograms of different samples were recorded at various scan rates and showed an increase in current density with an increase in scan rate. The sample with intermediate concentration of CTAB showed higher specific capacitance values. The sample with 0.09g CTAB showed efficient charge separation and poor charge recombination mechanism. The sample with 0.06g CTAB showed the highest energy density, power density, and specific capacitance. The samples exhibited battery-like charge storage mechanism and significant redox activity. The GCD curves of the samples exposed a triangular shape attributed to super capacitors. The study concludes that the CTAB hydrothermal process is very effective in controlling the properties of MoSe2/graphene nanosheets and holds a great potential for energy storage and conversion applications.