Enhanced photovoltaic performance and morphological control of the PbS counter electrode grown on functionalized self-assembled nanocrystals for quantum-dot sensitized solar cells via cost-effective chemical bath deposition

Thulasi-Varma, Chebrolu Venkata,Rao, S. Srinivasa,Ikkurthi, Kanaka Durga,Kim, Soo-Kyoung,Kang, Tae-Su,Kim, Hee-Je The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.39

<▼1><P>This study describes the synthesis of monodispersed PbS nanocrystals by a facile chemical bath deposition and cost-effective approach.</P></▼1><▼2><P>This study describes the synthesis of monodispersed PbS nanocrystals by a facile chemical bath deposition and cost-effective approach. PbS counter electrodes (CEs) were used to grow high-quality thin films containing cube-shaped nanocrystals or nanodendrites. The size and shape of the PbS nanocrystals can be easily controlled by varying the deposition time. Quantum dot-sensitized solar cells (QDSSCs) were made and showed improved performance using the PbS CEs obtained with a deposition time of 2 h. The nanocrystal structured PbS 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>sc) of 11.20 mA cm<SUP>−2</SUP>, an open circuit voltage (<I>V</I>oc) of 0.560 V, a fill factor (FF) of 0.55, and a power conversion efficiency (<I>η</I>) of 3.48%. These values are much higher than those of the Pt CE (<I>J</I>sc = 79.29 mA cm<SUP>−2</SUP>, <I>V</I>oc = 0.604, FF = 0.28, and <I>η</I> = 1.58%). The concentration of acetic acid plays an important role in deciding the size and shape of the PbS nanocrystals in the nucleation and growth process. The PbS strongly adhered to the FTO substrate due to the acetic acid, which acts as a stabilizer and a strong reagent in this one-step preparation. The performance of the PbS CE was improved by the surface morphology, which enables rapid electron transport and a lower electron recombination rate for the polysulfide electrolyte redox couple. Electrochemical impedance spectroscopy and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the PbS and Pt CEs.</P></▼2>

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>

Exploration of Ni-X (O, S, Se) for high performance supercapacitor with long-term stability via solution phase synthesis

Chebrolu Venkata Thulasi-Varma,Balamuralitharan Balakrishnan,Hee-JeKim 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-

Here, we report a simple strategy to grow NiSe architectures vertically on nickel foam (NF) via facilesolution-based deposition. The as-synthesized NSE7h core-shell nanoplate structure with a mass loadingof 6.4 mg/cm 2 can be delivered a high specific capacitance of 2234.84 Fg 1 at 10 mA cm 2 andoutstanding rate capability compared to that of NO (708.52 Fg 1), NS (968.22 Fg 1), NSE1h (1357.43 Fg 1),and NSE4h (1675.87 Fg 1). The desirable electrochemical performance was mainly attributed to thecomponent’s synergy assuring rich redox reactions, deposition of selenium on the surface of NiOnanotubes, high conductivity, great specific area and furthermore, rapid ion diffusion distance, witheffective transport pathway of electrons and electrolyte ions. The existence of selenium vacancies andversatile synthesis of NiSe architectures would open up a wide range of applications in energy storageand conversion applications including supercapacitors, electrocatalysis, and batteries.

Chemical bath deposition of NiCo₂S₄ nanostructures supported on a conductive substrate for efficient quantum-dot-sensitized solar cells and methanol oxidation

Kim, Hee-Je,Chebrolu, Venkata Thulasi-Varma The Royal Society of Chemistry 2018 NEW JOURNAL OF CHEMISTRY Vol.42 No.23

<P>Hierarchical nanostructures have recently attracted massive attention due to their remarkable performances in energy conversion, storage systems, catalysis, and electronic devices. Considering the advantage of hierarchical nanostructures, we have formulated a facile and cost-effective chemical bath deposition method to synthesize novel NiCo2S4 on a conductive substrate for quantum dot sensitized solar cells & methanol electro-oxidation. Owing to the unique nanoarchitecture, the NiCo2S4 electrodes were used to grow high quality thin films containing nanoflowers, nanoplatelets, or nanosheets. The nanoplate-structured NiCo2S4 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>sc) of 11.91 mA cm<SUP>−2</SUP>, open circuit voltage (<I>V</I>oc) of 0.602 V, fill factor (FF) of 0.50, and power conversion efficiency (<I>η</I>) of 3.53%. These values are much higher than those of the Pt CE (<I>J</I>sc = 6.98 mA cm<SUP>−2</SUP>, <I>V</I>oc = 0.579, FF = 0.36, and <I>η</I> = 1.10%). The electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry for NiCo2S4 electrodes <I>via</I> methanol electro-oxidation. Electrochemical studies reveal that the as-prepared NiCo2S4-NCS6h electrode displayed a significant enhancement in the electrocatalytic activity and stability for methanol oxidation in the presence of 2 M KOH with 0.5 M methanol. The results indicate that the hierarchical structure of NiCo2S4 offers a promising electrode material for QDSSCs and methanol electro-oxidation.</P>

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>

In situ synthesis of CuS nano platelets on nano wall networks of Ni foam and its application as an efficient counter electrode for quantum dot sensitized solar cells

Punnoose, Dinah,Kumar, Ch.S.S. Pavan,Rao, S. Srinivasa,Thulasi Varma, Chebrolu Venkata,Naresh, Bandari,Reddy, Araveeti Eswar,Kundarala, Nagabhushanam,Lee, Young-Seok,Kim, Mi-Young,Kim, Hee-Je ELSEVIER 2017 ORGANIC ELECTRONICS Vol.2017 No.42

Preparation and electrochemical performances of NiS with PEDOT:PSS chrysanthemum petal like nanostructure for high performance supercapacitors

S., Srinivasa Rao,Punnoose, Dinah,Bae, Jin-Ho,Durga, Ikkurthi Kanaka,Thulasi-Varma, Chebrolu Venkata,Naresh, Bandari,Subramanian, Archana,Raman, Vivekanandan,Kim, Hee-Je Elsevier 2017 ELECTROCHIMICA ACTA Vol.254 No.-

<P><B>Abstract</B></P> <P>This paper reports the facile synthesis of a novel architectural of NiS/PEDOT:PSS with DEG, where the complementary features of the three components (well-defined NiS black pepper like nanoparticles on nickel foam, an ultrathin layers of poly (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS), and diethylene glycol (DEG)) are deposited sequentially to a single entity to fabricate a high-performance electrode for supercapacitor applications. Owing to the high electrical conductivity of the well-defined NiS nanoparticles, in which the conductivity, and good chemical and electrochemical stability is enhanced further by the PEDOT:PSS and DEG thin layers, the as-fabricated NiS/PEDOT:PSS with a DEG chrysanthemum petal-like nanostructure exhibits good rate capability, excellent cycling stability, and high specific capacitance. The PEDOT:PSS with DEG offers extra conductive paths for each layer on NiS, yielding a lower internal resistance and charge-transfer resistance than that of the NiS/PEDOT:PSS without DEG. As a result, the NiS/PEDOT:PSS with the DEG electrode shows a tremendous pseudocapacitance of 750.64Fg<SUP>−1</SUP> at 1.11Ag<SUP>−1</SUP>, along with a high energy density of 24.52Whkg<SUP>−1</SUP> at a power density of 138.88Wkg<SUP>−1</SUP> and good cycling stability, suggesting that it is a promising candidate for energy storage. The unique performance of NiS/PEDOT:PSS with a DEG benefits from its unique chrysanthemum petal-like nanostructure, which could offer faster ion and electron transfer ability, greater reaction surface area and good structural stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> NiS/PEDOT:PSS with DEG chrysanthemum petals were prepared using a facile bar-coating method. </LI> <LI> NiS/PEDOT:PSS with DEG showed greater electrochemical properties. </LI> <LI> Improved penetration of electrolyte ions into the electrode was observed by the attachment PEDOT:PSS on NiS. </LI> <LI> The electrode exhibited a high specific capacitance of 750.64Fg<SUP>−1</SUP> at 1.11Ag<SUP>−1</SUP>. </LI> <LI> The nanocomposite displayed excellent cycling stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Reduced recombination with an optimized barrier layer on TiO₂ in PbS/CdS core shell quantum dot sensitized solar cells

Punnoose, Dinah,Pavan Kumar, CH. S. S.,Seo, Hyun Woong,Shiratani, Masaharu,Reddy, Araveeti Eswar,Srinivasa Rao, S.,Thulasi-Varma, Chebrolu Venkata,Kim, Soo-Kyoung,Chung, Sang-Hwa,Kim, Hee-Je The Royal Society of Chemistry 2016 New journal of chemistry Vol.40 No.4

<P>Fast electron transport and slow interfacial electron recombination are indispensable features for efficient photo-electrodes of quantum dot sensitized solar cells (QDSSCs). This study reports the methodology to prevent recombination losses in lead sulfide QDSSCs. TiO2 nano-particles were coated with two different insulating oxide materials (MgO and Al2O3). Single-and-double coated barrier layers are used in order to optimize the passivation effect, prevent recombination losses and to obtain high-performance stable QDSSCs when compared to bare TiO2. Metal oxides with a high isoelectric point enhance quantum dot adsorption and also increase the TiO2 conduction band edge. QDSSCs are examined in detail using a polysulfide electrolyte and a copper sulfide (CuS) counter electrode. A solar cell based on a double coating electrode (MgO/Al2O3) yielded excellent performance with an efficiency (eta) of 3.25%. The increase in electron transport and the decrease in electron recombination are responsible for the enhanced J(SC) and V-OC of QDSSCs. The electron lifetime with TiO2/MgO/Al2O3 was higher than those with bare TiO2, TiO2/MgO, TiO2/Al2O3 and TiO2/Al2O3/MgO leading to a more efficient electron-hole separation and slows down electron recombination.</P>

The influence of in situ deposition techniques on PbS seeded CdS/CdSe for enhancing the photovoltaic performance of quantum dot sensitized solar cells

Punnoose, D.,Suh, S.M.,Kim, B.J.,kim, S.k.,Kumar, Ch.S.S.P.,Rao, S.S.,Thulasi-Varma, C.V.,Reddy, A.E.,Chung, S.H.,Kim, H.J. Elsevier Sequoia 2016 Journal of Electroanalytical Chemistry Vol.773 No.-

<P>The deposition techniques of quantum dots (QDs) have great influence on the photovoltaic performances of quantum dot sensitised solar cells (QDSSCs). In this study, we report CdS/CdSe sensitised TiO2 solar cells focussing on the influence of two commonly used in situ QD deposition techniques (SILAR: successive ionic layer adsorption and reaction and CBD: chemical bath deposition). In addition to this, the QDSSC performance is enhanced due to better light harvesting capability of PbS quantum dots and makes large accumulation of photo-injected electrons in the conduction band of TiO2. When compared to power conversion efficiency (PCE) of 4.58% was obtained for PbS/CBD-CdS/CBD-CdSe cells when compared to PbS/SILAR-CdS/SILAR-CdSe. With chemical bath deposition, we achieved high surface coverage of QDs, which contributes to the increase in photocurrent,open circuit voltage and fill factor. Impedance spectroscopy revealed that the PbS/CBD-CdS/CBD-CdSe reduces recombination and increases charge collection efficiency and a long electron lifetime was achieved. To associate the assembling of QDs with the performance of QDSSCs a methodical characterization of morphology, optical and electro-chemical properties and its stability has been studied. We achieved PbS seeded CBD highlighting its robust consequences for the performance of QDSSCs. (C) 2016 Elsevier B.V. All rights reserved.</P>