Influence of Mn⁺² incorporation in CdSe quantum dots for high performance of CdS-CdSe quantum dot sensitized solar cells

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>

Performance enhancement of quantum dot-sensitized solar cells based on polymer nano-composite catalyst

Seo, Hyunwoong,Gopi, Chandu V.V.M.,Kim, Hee-Je,Itagaki, Naho,Koga, Kazunori,Shiratani, Masaharu Elsevier 2017 ELECTROCHIMICA ACTA Vol.249 No.-

<P><B>Abstract</B></P> <P>Polymer nano-composite composed of poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) and TiO<SUB>2</SUB> nano-particles was deposited on fluorine-doped tin oxide substrate and applied as an alternative to Au counter electrode of quantum dot-sensitized solar cell (QDSC). It became surface-richer with the increase in nano-particle amount so that catalytic reaction was increased by widened catalytic interface. Electrochemical impedance spectroscopy and cyclic voltammetry clearly demonstrated the enhancement of polymer nano-composite counter electrode. A QDSC based on polymer nano-composite counter electrode showed 0.56V of V<SUB>OC</SUB>, 12.24mAcm<SUP>−2</SUP> of J<SUB>SC</SUB>, 0.57 of FF, and 3.87% of efficiency and this photovoltaic performance was higher than that of QDSC based on Au counter electrode (3.75%).</P> <P><B>Highlights</B></P> <P> <UL> <LI> We studied polymer nano-composite containing TiO<SUB>2</SUB> nano-particles as a catalyst. </LI> <LI> Polymer nano-composite was applied for quantum dot-sensitized solar cells. </LI> <LI> Polymer nano-composite catalyst was considerably improved with TiO<SUB>2</SUB> nano-particles. </LI> <LI> Polymer nano-composite showed higher photovoltaic performance than conventional Au. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigation on novel CuS/NiS composite counter electrode for hindering charge recombination in quantum dot sensitized solar cells

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>

Reply to ''Comment on ''Facile chemical bath deposition of CuS nano peas like structure as a high efficient counter electrode for quantum-dot-sensitized solar cells'' by H.-J. Kim, J.-H. Kim, CH. S. S. Pavan Kumar, D. Punnoose, S.-K. Kim, C. V. V. M. Gop

Kim, H.J.,Kim, J.H.,Pavan Kumar, C.H.S.S.,Punnoose, D.,Kim, S.K.,Gopi, C.V.V.M.,Rao, S.S. Elsevier Sequoia 2015 Journal of Electroanalytical Chemistry Vol.756 No.-

Highly effective nickel sulfide counter electrode catalyst prepared by optimal hydrothermal treatment for quantum dot-sensitized solar cells

Gopi, Chandu V.V.M.,Srinivasa Rao, S.,Kim, Soo-Kyoung,Punnoose, Dinah,Kim, Hee-Je Elsevier 2015 Journal of Power Sources Vol.275 No.-

<P><B>Abstract</B></P> <P>Nickel sulfide (NiS) thin film has been deposited on a fluorine-doped tin oxide substrate by a hydrothermal method using 3-mercaptopropionic acid and used as an efficient counter electrode (CE) for polysulfide redox reactions in quantum dot-sensitized solar cells (QDSSCs). NiS has low toxicity and environmental compatibility. In the present study, the size of the NiS nanoparticle increases with the hydrothermal deposition time. The performance of the QDSSCs is examined in detail using polysulfide electrolyte with the NiS CE. A TiO<SUB>2</SUB>/CdS/CdSe/ZnS-based QDSSC using the NiS CE shows enhanced photovoltaic performance with a power conversion efficiency (PCE) of 3.03%, which is superior to that of a cell with Pt CE (PCE 2.20%) under one sun illumination (AM 1.5, 100 mW cm<SUP>−2</SUP>). The improved photovoltaic performance of the NiS-based QDSSC may be attributed to a low charge transfer resistance (5.08 Ω) for the reduction of polysulfide on the CE, indicating greater electrocatalytic activity of the NiS. Electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the NiS and Pt CEs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nickel sulfide is used as counter electrode of quantum dots-sensitized solar cell. </LI> <LI> Nickel sulfide shows superior electro-catalytic activity than Pt. </LI> <LI> The content of sulfur in nickel sulfide thin film depends on the deposition time. </LI> <LI> The QDSSC using NiS CE yield a high PCE value of 3.03%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Low-temperature easy-processed carbon nanotube contact for high-performance metal- and hole-transporting layer-free perovskite solar cells

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.

A strategy to improve the energy conversion efficiency and stability of quantum dot-sensitized solar cells using manganese-doped cadmium sulfide quantum dots

Gopi, Chandu V. V. M.,Venkata-Haritha, M.,Kim, Soo-Kyoung,Kim, Hee-Je The Royal Society of Chemistry 2015 Dalton Transactions Vol.44 No.2

<P>This article describes the effect of manganese (Mn) doping in CdS to improve the photovoltaic performance of quantum dot sensitized solar cells (QDSSCs). The performances of the QDSSCs are examined in detail using a polysulfide electrolyte with a copper sulfide (CuS) counter electrode. Under the illumination of one sun (AM 1.5 G, 100 mW cm<SUP>−2</SUP>), 10 molar% Mn-doped CdS QDSSCs exhibit a power conversion efficiency (<I>η</I>) of 2.85%, which is higher than the value of 2.11% obtained with bare CdS. The improved photovoltaic performance is due to the impurities from Mn<SUP>2+</SUP> doping of CdS, which have an impact on the structure of the host material and decrease the surface roughness. The surface roughness and morphology of Mn-doped CdS nanoparticles can be characterised from atomic force microscopy images. Furthermore, the cell device based on the Mn-CdS electrode shows superior stability in the sulfide/polysulfide electrolyte in a working state for over 10 h, resulting in a highly reproducible performance, which is a serious challenge for the Mn-doped solar cell. Our finding provides an effective method for the fabrication of Mn-doped CdS QDs, which can pave the way to further improve the efficiency of future QDSSCs.</P> <P>Graphic Abstract</P><P>Better stability and higher performance of Mn-doped CdS QDSSCs (PCE = 2.85%) than those of CdS QDSSCs (PCE = 2.11%). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4dt03063j'> </P>

Improved photovoltaic performance and stability of quantum dot sensitized solar cells using Mn-ZnSe shell structure with enhanced light absorption and recombination control

Gopi, Chandu V. V. M.,Venkata-Haritha, M.,Kim, Soo-Kyoung,Kim, Hee-Je The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.29

<P>To make quantum-dot-sensitized solar cells (QDSSCs) competitive, photovoltaic parameters comparable to those of other emerging solar cell technologies are necessary. In the present study, ZnSe was used as an alternative to ZnS, one of the most widely used passivation materials in QDSSCs. ZnSe was deposited on a TiO2-CdS-CdSe photoanode to form a core-shell structure, which was more efficient in terms of reducing the electron recombination in QDSSCs. The development of an efficient passivation layer is a requirement for preventing recombination processes in order to attain high-performance and stable QDSSCs. A layer of inorganic Mn-ZnSe was applied to a QD-sensitized photoanode to enhance the adsorption and strongly inhibit interfacial recombination processes in QDSSCs, which greatly improved the power conversion efficiency. Impedance spectroscopy revealed that the combined Mn doping with ZnSe treatment reduces interfacial recombination and increases charge collection efficiency compared with Mn-ZnS, ZnS, and ZnSe. A solar cell based on the CdS-CdSe-Mn-ZnSe photoanode yielded excellent performance with a solar power conversion efficiency of 5.67%, Voc of 0.584 V, and Jsc of 17.59 mA cm(-2). Enhanced electron transport and reduced electron recombination are responsible for the improved Jsc and Voc of the QDSSCs. The effective electron lifetime of the device with Mn-ZnSe was higher than those with Mn-ZnS, ZnSe, and ZnS, leading to more efficient electron-hole separation and slower electron recombination.</P>

Improving the performance of quantum dot sensitized solar cells through CdNiS quantum dots with reduced recombination and enhanced electron lifetime

Gopi, Chandu V. V. M.,Venkata-Haritha, Mallineni,Seo, Hyunwoong,Singh, Saurabh,Kim, Soo-Kyoung,Shiratani, Masaharu,Kim, Hee-Je The Royal Society of Chemistry 2016 Dalton Transactions Vol.45 No.20

<P>To make quantum dot-sensitized solar cells (QDSSCs) competitive, we investigated the effect of Ni2+ ion incorporation into a CdS layer to create long-lived charge carriers and reduce the electron-hole recombination. The Ni2+ -doped CdS (simplified as CdNiS) QD layer was introduced to a TiO2 surface via the simple successive ionic layer adsorption and reaction (SILAR) method in order to introduce intermediateenergy levels in the QDs. The effects of different Ni2+ concentrations (5, 10, 15, and 20 mM) on the physical, chemical, and photovoltaic properties of the QDSSCs were investigated. The Ni2+ dopant improves the light absorption of the device, accelerates the electron injection kinetics, and reduces the charge recombination, which results in improved charge transfer and collection. The 15% CdNiS cell exhibits the best photovoltaic performance with a power conversion efficiency (eta) of 3.11% (J(SC) = 8.91 mA cm(-2), VOC = 0.643 V, FF = 0.543) under one full sun illumination (AM 1.5 G). These results are among the best achieved for CdS-based QDSSCs. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) measurements confirm that the Ni2+ dopant can suppress charge recombination, prolong the electron lifetime, and improve the power conversion efficiency of the cells.</P>

Time Varied Morphology Controllable Fabrication of NiS Nanosheets Structured Thin Film and its Application as a Counter Electrode for QDSSC

Thulasi-Varma, Chebrolu Venkata,Gopi, Chandu V. V. M.,Rao, S. Srinivasa,Punnoose, Dinah,Kim, Soo-Kyoung,Kim, Hee-Je American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.21

<P>A novel strategy has been successfully developed for highly efficient nanosheet-structured NiS counter electrodes. The NiS was deposited on FTO substrate with different deposition times using the simple and cost-effective chemical bath deposition technique. The NiS CEs were used to grow high quality thin films containing nanoparticles, nanosheets, or nanorods. The nanosheet-structured NiS CE in QDSSCs under one-sun illumination (AM 1.5, 100 Mw cm<SUP>–2</SUP>) yielded a high short circuit current density (<I>J</I><SUB>sc</SUB>) of 13.53 mA cm<SUP>–2</SUP>, open circuit voltage (<I>V</I><SUB>oc</SUB>) of 0.570 V, fill factor (FF) of 0.450, and power conversion efficiency (η) of 3.47%. These values are much higher than those of the Pt CE (<I>J</I><SUB>sc</SUB> = 7.85 mA cm<SUP>–2</SUP>, <I>V</I><SUB>oc</SUB> = 0.611, FF = 0.243, and η = 1.170%). The NiS was strongly adhered on the FTO substrate by acetic acid which acts as stabilizer and strong reagent in this one step preparation. The performance of NiS CE was improved by the surface morphology, which enable rapid electron transport and a lower electron recombination rate for the polysulfide electrolyte redox couple. In the present study NiS has obtained higher electrocatalytic activity which plays a crucial role in the QDSSC. Electrochemical impedance spectroscopy and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the NiS and Pt CEs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-21/acs.jpcc.5b01771/production/images/medium/jp-2015-01771s_0001.gif'></P>