Kelechi Chiemezie Nwambaekwe

This work introduces a novel Cu ₂ ZnSnS ₄ (copper zinc tin sulfide [CZTS]) kesterite/coconut shell‐derived biomass activated carbon (AC) nanocomposite material (CZTS _0.5 :AC _0.5 ) for supercapacitor application. CZTS was prepared by microwave‐assisted synthesis and combined with AC to produce CZTS _0.5 :AC _0.5 through mechanical milling and low‐temperature annealing at 350°C. X‐ray diffraction (XRD) and Raman spectroscopic analyses of CZTS _0.5 :AC _0.5 nanocomposite revealed the formation of a multiphase system consisting of residual CZTS and secondary sulfides (zinc sulfide [ZnS], CuS, and SnS), which are embedded within a highly conductive amorphous carbon matrix. High‐resolution transmission electron microscopy (HRTEM) results indicate a reduction of the particle size from 55.7 nm (for CZTS) to 21.7 nm (for CZTS _0.5 :AC _0.5 ) due to annealing. The nanostructurization of CZTS _0.5 :AC _0.5 created abundant electroactive sites that made the material an efficient charge storage system. Galvanostatic studies of AC//CZTS _0.5 :AC _0.5 in a three‐electrode configuration produced a specific capacitance ( C _sp ) of 458.2 Fg ⁻¹ at 1 Ag ⁻¹ . Two‐electrode AC//CZTS _0.5 :AC _0.5 asymmetric supercapacitor device had a maximum energy density of 12.8 Wh kg ⁻¹ and a maximum power density of 890.5 W kg ⁻¹ . The supercapacitor device exhibited excellent stability with a coulombic efficiency retention of 99.99% and a capacitance retention of 81.4% after 10,000 cycles. The results portray CZTS _0.5 :AC _0.5 nanocomposite material as a promising, sustainable electrode material for next‐generation supercapacitors.

To generate and deliver alternative sustainable energy in the face of the current energy crisis, new materials that can capture solar energy and transform it into other useful energies are required. Rare-earth (RE) oxychalcogenides are now being used more frequently as up/down-conversion materials in established photovoltaic (PV) devices to boost their PV performance. Here, through an efficient microwave assisted synthesis procedure, novel nanoplate/sheet shaped nanomaterials of yttrium oxyselenide (YOSe) and its analogues doped with Tb and Eu (YOSe:Tb and YOSe:Eu) were successfully synthesized. Analyses of the structure, stability, morphology, light absorption, and electrochemistry were performed. This work showed that the parent YOSe exhibited green (543 nm) and red (615 nm) emission luminescence when doped with Tb and Eu with a luminescence quantum yield (LQY) of 0.56 and 0.53 for YOSe:Tb and YOSe:Eu nanomaterials, respectively. The surface and material conductivity of YOSe improved with the addition of the dopant elements, with the best outcome shown in YOSe:Eu, according to electrokinetic research evidenced by the enhanced current peaks, reduced charge-transfer resistance (R_ct) and low impedance magnitude (Z_mag) through electrochemical experiments. These improvements were induced by the distinctive properties of the dopant elements. PCEs of 0.25%, 0.67%, and 1.20% were obtained for YOSe, YOSe:Tb, and YOSe:Eu-based PV devices, respectively, using the nanomaterials as novel absorber layers in a superstrate device design. Our results can initiate further exploitation of the doped host structure for effective down-conversion NIR luminescence for applications in PV devices and to boost the PV performance of existing solar cells.