Ashim Gurung

8-Hydroxylquinoline as a strong alternative anchoring group for porphyrin-sensitized solar cells.

8-Hydroxylquinoline (OQ) is demonstrated for the first time as a strong alternative anchoring group porphyrin dyes to improve the long-term stability of solar cells.

Binder Free Hierarchical Mesoporous Carbon Foam for High Performance Lithium Ion Battery

A hierarchical mesoporous carbon foam (ECF) with an interconnected micro-/mesoporous architecture was prepared and used as a binder-free, low-cost, high-performance anode for lithium ion batteries. Due to its high specific surface area (980.6 m2/g), high porosity (99.6%), light weight (5 mg/cm3) and narrow pore size distribution (~2 to 5 nm), the ECF anode exhibited a high reversible specific capacity of 455 mAh/g. Experimental results also demonstrated that the anode thickness significantly influence the specific capacity of the battery. Meanwhile, the ECF anode retained a high rate performance and an excellent cycling performance approaching 100% of its initial capacity over 300 cycles at 0.1 A/g. In addition, no binders, carbon additives or current collectors are added to the ECF based cells that will increase the total weight of devices. The high electrochemical performance was mainly attributed to the combined favorable hierarchical structures which can facilitate the Li+ accessibility and also enable the fast diffusion of electron into the electrode during the charge and discharge process. The synthesis process used to make this elastic carbon foam is readily scalable to industrial applications in energy storage devices such as li-ion battery and supercapacitor.

Higher efficiency perovskite solar cells using additives of LiI, LiTFSI and BMImI in the PbI2 precursor

The efficiencies of perovskite solar cells have been significantly increased to 18%, 17.01% and 15.6% for the cells containing the additives BMImI, LiI and LiTFSI in the PbI2 precursor solutions, respectively, from 11.3% for the devices without any additives. Incorporation of these additives led to the formation of perovskites with larger grain size and higher crystallinity with reduced PbI2 residue as indicated by X-ray diffraction (XRD) and atomic force microscopy (AFM) results. Kelvin Probe Force Microscopy (KPFM) and current sensing (CS)-AFM results were in good agreement with external quantum efficiency (EQE) measurements and proved the great enhancement in short circuit current density (Jsc) as a result of doping. Transient photovoltage measurement results exhibited longer charge carrier lifetimes for the additive incorporated perovskites than those without additives, thus improving the fill factor (FF) and open circuit voltage (Voc). In addition to the improved efficiency, the incorporation of these additives led to higher stability of the CH3NH3PbI3 perovskite solar cells. The new additive BMImI, LiI and LiTFSI incorporated CH3NH3PbI3 perovskite solar cells exhibited a reduced degradation with a 57%, 60%, and 91% decrease in performance respectively after exposure to air for 70 days compared to a 93% decrease for the pristine cell after only 24 days. The lithium salt additives can serve as desiccants to absorb moisture preventing perovskite degradation. Further, the BMImI additive can prevent the formation of free radicals in perovskites upon exposure to light and heat.

Urea treated WO 3 and SnO 2 as cost effective and efficient counter electrodes of dye sensitized solar cells

A novel method was developed to convert the electro-catalytically inactive commercial WO₃ and SnO₂ into high efficient WO_3-x and SnO_2-x counter electrodes for dye sensitized solar cells (DSSs) to replace Pt. Both WO₃ and SnO₂ was treated with Urea with different Urea mass ratio concentrations and annealed under N₂ environment at 500°C. The energy conversion efficiency (PEC) was significantly improved by urea treatment with 8.57% compared to 2.91 % for non-treated CE in case of WO₃ and increases from 2.76 % for non-treated CE to 8.7 % after urea treatment in case of SnO₂. All other characterizations performed for urea treated WO₃ and SnO₂ support the hypothesis of creating oxygen vacancies inside the metal oxides by the treatment. These oxygen vacancies facilitate the redox process in iodide/trioxide electrolyte. The density of these oxygen vacancies could be controlled by controlling the urea concentration during the treatment.