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Venkata-Haritha, M.,V.V.M. Gopi, C.,Thulasi-Varma, C.V.,Kim, S.K.,Kim, H.J. Elsevier Sequoia 2016 Journal of photochemistry and photobiology Chemist Vol.315 No.-
<P>Quantum dot sensitized solar cells (QDSSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective and facile fabrication of solar cell with improved photovoltaic performance. QDs were directly grown on the TiO2 mesostructure by the successive ionic layer absorption and reaction (SILAR) technique. QDSSC based on CdS-CdSe photoanode achieves a power conversion efficiency of 3.42% under AM 1.5 G one sun illumination. The loading of Mn+2 metal ions was applied to a CdSe (CdS-Mn-CdSe) photoanode to enhance the absorption in QDSSCs, which greatly improved the power conversion efficiency. Without the passivation layer, the solar cell based on a CdS-Mn-CdSe QD-sensitized TiO2 photoelectrode shows higher J(sc) (14.67 mA/cm(2)), V-oc (0.590 V) and power conversion efficiency (4.42%) comparing to Mn-undoped CdS-CdSe QD sensitized TiO2 (J(sc): 11.29 mA/cm(2), V-oc: 0.568 V, and efficiency: 3.42%), which can be ascribed to superior light absorption, faster electron transport and slower charge recombination for the former. The effective electron lifetime of the device with CdS-Mn-CdSe was higher than those with CdS-CdSe, leading to more efficient electron-hole separation and slower electron recombination. The effects of Mn+2 metal ions on the chemical, physical, and photovoltaic properties of the QDSSCs have been investigated have been investigated by X-ray photon spectroscopy (XPS), UV-vis spectra, photocurrent-voltage (J-V) characteristics and electrochemical impedance spectra (EIS). (C) 2015 Elsevier B.V.All rights reserved.</P>
Kim, H.J.,Suh, S.M.,Rao, S.S.,Punnoose, D.,Tulasivarma, C.V.,Gopi, Chandu.V.V.M.,Kundakarla, N.,Ravi, S.,Durga, I.K. Elsevier Sequoia 2016 Journal of Electroanalytical Chemistry Vol.777 No.-
<P>To make quantum dot-sensitized solar cells (QDSSCs) more attractive, it is necessary for the power conversion efficiency (PCE) to be comparable to those of other emerging solar cells. Currently, copper sulfide (CuS) and nickel sulfide (NiS) are commonly used counter electrodes (CEs) in high-efficiency QDSSCs because of their low toxicity, environmental compatibility, and superior electrocatalytic activity in the presence of polysulfide electrolyte. For the first time, novel CuS/NiS electrodes were prepared by facile chemical bath deposition method. This article describes the effect of NiS layer on CuS film for preventing the recombination process to enhance the performance of QDSSCs. Under one sun illumination, the CE with the optimized CuS/NiS composite film exhibits higher short-circuit current density (J(sc)), open-circuit voltage (V-oc), and PCE of 12.47 mA cm(-2), 0.599 V, and 4.19%, respectively. These values are much higher than those of bare CuS (2.73%), NiS (1.82%), and Pt CEs (1.16%). This enhancement is mainly attributed to the improved surface morphology, higher sulfur atomic percentage with Cu vacancies, rapid electron transport, and lower electron recombination rate for the polysulfide electrolyte. Characterization with, cyclic voltammetry, and Tafel polarization was performed to study the reasons for efficient CE performance. (C) 2016 Elsevier B.V. All rights reserved.</P>
Gopi, C.V.V.M.,Venkata-Haritha, M.,Prabakar, K.,Kim, H.J. Elsevier Sequoia 2017 Journal of photochemistry and photobiology. A, Che Vol.332 No.-
Expensive and energy-consuming vacuum process of metal deposition with ambient-unstable hole transporters are incompatible with large-scale and low-cost production of perovskite solar cells (PSCs) and thus hampers their commercialization. For the first time, we demonstrate cost-effective novel carbon nanotube (CNT) paste that was applied to FTO substrate by the facile doctor blade method and processed at low temperature (100<SUP>o</SUP>C). Herein we report a new method of cost-efficient perovskite solar cells with the use of conventional hole transporters by directly clamping a selective hole extraction electrode made of CNT and a TiO<SUB>2</SUB>/perovskite photoanode. Most importantly, under optimized conditions in the absence of an organic hole-transporting material and metal contact, CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> and CNTs formed a solar cell with an efficiency of up to 7.83%. The PSC devices are fabricated in air without high-vacuum deposition which simplifies the processing and lowers the threshold of both scientific research and industrial production of PSCs. Electrochemical impedance spectroscopy demonstrates good charge transport characteristics of CEs on the photovoltaic performance of devices. The PSCs exhibited good stability over 50h. The abundance, low cost, and excellent properties of the CNT material offer wide prospects for further applications in PSCs.
Gopi, C. V.,Venkata-Haritha, M.,Lee, Y. S.,Kim, H. J. Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.21
<P>As a promising type of new-generation solar cells, the electrocatalytic activity and stability of counter electrodes (CEs) play a key role in the performance of QDSSCs (quantum-dot-sensitized solar cells) at present. Here, a facile solution-processing method for fabricating metal sulfides (CoS, NiS, CuS and PbS) on vertically aligned ZnO nanorods (NRs) has been demonstrated and used to produce efficient CEs in polysulfide electrolyte-based QDSSCs. Compared with bare metal sulfide CEs (CoS, NiS, CuS and PbS), the ZnO NR framework presents a larger surface area for loading more metal sulfide catalysts and easy accessibility of the electrolyte. Additionally, the metal sulfide catalyst with high catalytic activity plays the main role in the reduction of the oxidized polysulfide, white the ZnO NRs offer an excellent electron pathway for shuttling electrons to highly catalytic metal sulfide sites and facilitate charge transport during catalysis. Cyclic voltammetry measurements indicate that the ZnO/PbS CEs still retain good cyclability after 50 cycles, demonstrating super-stability, while the ZnO/CoS, ZnO/NiS, ZnO/CuS, and Pt CEs show obvious fluctuations. Therefore, the ZnO/PbS CE exhibits much higher catalytic activity with the polysulfide electrolyte than ZnO/CoS, ZnO/NiS, ZnO/CuS and Pt CEs. As a result, a QDSSC based on the ZnO/PbS CE achieves a power conversion efficiency (eta) of 4.76%, which is attributed to the high fill factor (FF) of 0.566, and the eta is much higher than that based on ZnO/CoS (2.75%), ZnO/NiS (3.12%), ZnO/CuS (4.10%) and Pt (1.54%) CEs. The excellent catalytic performance along with the facile preparation of ZnO NRs decorated with metal sulfide CE materials make them a distinctive choice among the various CEs studied.</P>
D. Gopi,P.R. Bhalaji,V.C.A. Prakash,A.K. Ramasamy,L. Kavitha,J.M.F. Ferreira 한국물리학회 2011 Current Applied Physics Vol.11 No.3
A method to synthesize hydroxyapatite (HAP) ceramic powders using a metal-oxalate route with calcium chloride and phosphoric acid as calcium and phosphorus precursors respectively is described. Ethylene glycol was used as a reaction medium and oxalic acid as a chelating agent. The resulting HAP powders were calcined at 600 ℃ for 6 h and subsequently sintered at 900 ℃ for 2 h. FT-IR, XRD and SEM techniques were employed for the characterization of the synthesized particles. Moreover, the influence of reaction temperature on the HAP formation was also studied. The results have shown successful formation of the crystalline, uniform sized, uniform shaped and stoichiometric HAP powders at a reaction temperature of 75 ℃ which was found to be the optimum temperature for the preparation. The grain size of the synthesized sample was 680 nm in length and 440 nm in width.
Lee, Y.S.,Gopi, C.V.V.M.,Venkata-Haritha, M.,Rao, S.S.,Kim, H.J. Elsevier Sequoia 2017 Journal of photochemistry and photobiology Chemist Vol. No.
The high stability and superior electrocatalytic activity of counter electrodes (CEs) are crucial but important issues in high performance quantum dot-sensitized solar cells (QDSSCs). To address the above issues, nanoparticle-structured nickel sulfide (NiS) thin film electrodes were prepared on F-doped SnO<SUB>2</SUB> glass (FTO glass) substrates using a facile chemical bath deposition method at different growth times and used directly as the CEs for CdS/CdSe/ZnS QDSSCs. The surface morphology and thickness of the resulting NiS films are greatly affected by the deposition time. By optimizing the growth time of the NiS CE materials, a power conversion efficiency up to 3.25% was achieved for CdS/CdSe/ZnS based QDSSCs, which was much higher than that of the Pt CE (0.79%). In addition, a preliminary durability test of the CE in QDSSCs reveals that the NiS CE exhibited good stability than the Pt CE. The improved performance of the QDSSC was attributed to the resulting electrochemical catalytic activity of the NiS CE with efficient charge transfer at the CE/electrolyte interface, which was verified by the electrochemical impedance spectroscopy and the Tafel polarization measurement results. Therefore, the excellent electrochemical performance of NiS highlights its promising application as a CE for high performance QDSSCs.
Kim, H.J.,Kim, J.H.,Pavan Kumar, CH.S.S.,Punnoose, D.,Kim, S.K.,Gopi, C.V.V.M.,Srinivasa Rao, S. Elsevier Sequoia 2015 Journal of Electroanalytical Chemistry Vol.739 No.-
In this paper, highly efficient nano peas like structure CuS film has been successfully employed in quantum dot sensitized solar cells (QDSSCs) for its highest catalytic activity at minimal cost. The CuS thin film electrode was deposited on fluorine-doped tin oxide (FTO) substrate by chemical bath deposition technique using urea at low deposition temperatures. This electrode elevated the short circuit current and fill factor in comparison to the frequently used Pt electrode. Moreover, electrochemical measurement data disclosed higher electrocatalytic activity toward polysulfide reduction. The CuS film exhibited an average particle size of 180-270nm and film thickness of 825nm. It also revealed superior J<SUB>sc</SUB> (13.87mA/cm<SUP>2</SUP>) and conversion efficiency of 4.01% which is remarkably higher than that of the Pt-based cell (1.07%). In addition, stability test conducted for both CuS and Pt-based cells for about 900min at working conditions affirmed that the long-term stability of the CuS film decreased by 16.66% (4.02-3.35%), while that of the Pt based cell got elevated by 24.29% until 700min, and consequently diminished by 8.27% from 700 to 900min.