Browsing by Author "Kumari, J.M.K.W."

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    Application of Thermally Reduced Graphene Oxide-based Counter Electrode for Dye- sensitized Solar Cells: A Comparative Study on Sintering Temperature
    (Uva Wellassa University of Sri Lanka, 2021) Kumari, J.M.K.W.; Dissanayake, M.A.K.L.; Senadeera, G.K.R.
    A counter electrode (CE) fabricated with thermally reduced graphene oxide synthesized from Sri Lankan graphite is proposed for promising Platinum-free dye sensitized solar cells (DSSC). As it is well known, Sri Lankan natural graphite has become more attractive and demanding in the world due to its high purity and high crystallinity. In a DSSC, a thin film of Platinum (Pt) is generally used as the catalytic material on the CE due to its high conductivity and superior electro-catalytic activity. However, there is a considerable attention to replace Pt based CEs due to their high cost and limited supply. Recently, extensive research has been performed on using carbon materials for the CEs due to their low cost, high conductivity and good catalytic activity. In this study, reduced graphene oxide (RGO) was synthesized and deposited on FTO conducting glass substrate by spray method. To investigate the effect of sintering temperature of the CE on the performance of DSSCs, a series of RGO based CEs were prepared with different sintering temperatures from 100 oC to 300 oC by increasing the temperature by 50 oC intervals. Results confirmed that the DSSCs prepared with sintered CEs exhibit a better photovoltaic performance compared to the DSSCs made with un- sintered CEs essentially due to the enhanced adhesion to the FTO glass substrate in the sintered composite material. DSSCs with CEs sintered at 250 oC have exhibited the highest efficiency of 4.52 % compared to the DSSC with un-sintered CEs (efficiency=1.35 %). This low cost RGO CE exhibits good stability and acceptable efficiency compared to Pt CE (7.82 %) in DSSCs operating under similar conditions. Synthsized RGO sheets were characterized using scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The electro-catalytic activity of RGO CE was determined by cyclic voltammetry. Results suggested that this CE can be one of the alternatives to the Pt CEs in DSSCs with further modifications. Keywords: Dye sensitized solar cells; Counter electrode; Reduced graphene oxide; Sintering temperature
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    Effect of 4-tertbutyl pyridine and guanidinium thiocyanate Co-Additives on Performance of Dye-Sensitized Solar Cells Fabricated with Non-Volatile Liquid Electrolyte
    (Uva Wellassa University of Sri Lanka, 2021) Umair, K.; Dissanayake, M.A.K.L.; Senadeera, G.K.R.; Kumari, J.M.K.W.
    Dye-sensitized solar cells (DSSCs) are emerging as potential candidates to substitute for expensive silicon solar cells because of reasonably high efficiency, easy fabrication method, lower production cost and transparency. Electrolyte modifications of DSSC are an easy way to enhance the photovoltaic performance. The conventional liquid electrolyte system is composed of iodide/triiodide single salt in the volatile, acetonitrile solvent. In this work, the non-volatile ethylene carbonate (EC) and propylene carbonate (PC) were used with tetrapropyl ammonium iodide (Pr4NI) salt to prepare the reference electrolyte. The effect of the co- additives 4-tert butylpyridine (TBP) and Guanidinium thiocyanate (GuSCN) on the photovoltaic performance of DSSCs was also studied. The addition of TBP as an additive into the iodide electrolyte system increased the photovoltage (VOC) by 13.8%, but it reduced the photocurrent density (JSC) by 7.2%. However, the JSC was increased by about 8.7% by the addition of GuSCN as the additive. The addition of the combination of TBP and GuSCN binary additives in the optimized ratio of 65:35 enhanced the cell efficiency from 5.63% to 6.83%. The overall efficiency enhancement has been explained by the shifting of the conduction energy band edge of TiO2 due to the adsorption of species from the two co-additives by TiO2 leading to the enhancement of both, the photocurrent density as well as the photovoltage. TBP improves the VOC by a negative shift of the band-edge and also prevents the electron recombination to I3- due to the blocking effect on the dye-absent active site of the TiO2 surface. The addition of GuSCN to TBP-added electrolyte restored the JSC by the positive shift of the band-edge. The net effect is to increase the overall performance of DSSCs due to the synergistic effect of the two co-additives. Keywords: Photovoltaic effect; Co-additives; Band-edge shift; Non-volatile; VOC improver
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    Enhanced Photovoltaic Properties of Cadmium Sulfide Quantum Dot Sensitized TiO2 Solar Cells with Novel SnO2 Based Counter Electrode
    (Uva Wellassa University of Sri Lanka, 2021) Sandamali, W.I.; Senadeera, G.K.R.; Dissanayake, M.A.K.L.; Jaseetharan, T.; Kumari, J.M.K.W.; Umair, K.; Perera, V.P.S.; Rajendra, J.C.N.; Karthikeyan, N.
    Quantum dot sensitized solar cells (QDSSCs) have gained increased attention due to the unique properties of the semiconductor quantum dots (QDs), as light captivating materials. QDs facilitates multiple exciton generation, tunable bandgaps, high absorption coefficient, and low power consumption. Many studies have been carried out towards producing affordable QDSSCs with high power conversion efficiencies, utilizing these properties. As a critical component of QDSSCs, counter electrodes hold significant importance among these studies. Platinum (Pt), a widely used counter electrode with QDSSCs, is being disfavored due to high cost, diminishing material supply, and reduced catalytic activity, when used with polysulfide electrolyte which is the most common electrolyte for QDSSCs, due to surface, adsorbed sulphur. Therefore, substantial investigations have been carried out in searching for an alternative, affordable and effective counter electrode in these devices. Among the suitable materials, tin oxide (SnO2), a wide bandgap semiconductor, has become a promising candidate for counter electrode due to its high chemical stability, high electron mobility, low cost and environmentally friendly nature. In this study, counter electrodes were fabricated by depositing SnO2 films on fluorine-doped tin oxide (FTO) glass substrates by using a simple spray pyrolysis technique. These counter electrodes were characterized by scanning electron microscopic and Raman techniques. Photovoltaic properties of CdS quantum dots sensitized TiO2 solar cells with polysulfide electrolyte were tested by using this novel counter electrode. QDSSCs fabricated with optimized SnO2 counter electrode showed 1.47% power conversion efficiency under the illumination of 100 mW cm-2, whereas the devices fabricated with conventional Pt coated counter electrodes showed 1.08% under the same conditions. Therefore, about 36% enhancement in power conversion efficiency could be obtained by employing this novel low-cost counter electrode in these QDSSCs. Keywords: Counter electrode; SnO2; CdS; Quantum dot sensitized solar cell