Counter Electrode For Quantum Dot-sensitized Solar Cells Research Articles

Phosphorus doped CuS as an advanced counter electrode for quantum dot-sensitized solar cells

Developing an efficient material as a counter electrode (CE) with excellent catalytic activity and low cost is essential for the commercial application of quantum dot-sensitized solar cells (QDSSCs). Transition metal phosphides and sulfides have been demonstrated as outstanding multifunctional catalysts in a broad range of energy conversion technologies. Herein, we exploited an advanced phosphorus doped copper sulfide (P-doped CuS) as CEs in QDSSCs. P-doped CuS was synthesized by a hydrothermal process and subsequently a process for phosphatizing CuS in a tube furnace at 270 °C with NaH2PO2 as the phosphorus source. The morphology, composition and crystalline phase of P-doped CuS have been studied by X-ray and electron-based characterizations (XRD, SEM, TEM and XPS). The photovoltaic parameters of QDSSCs based on P-doped CuS CEs show an obvious dependence on the P-doping concentration, and QDSSCs based on the P-doped CuS CE with 1.9% P-doping yield a maximum power conversion efficiency of 3.45%, a 36% improvement over the QDSSCs based on the CuS CEs. Electrochemical impedance spectroscopy, Tafel polarization and cyclic voltammetry measurements showed that the electrocatalytic activity of P-doped CuS CEs in the S2−/Sn2− redox reaction was higher than that of CuS CEs, which supported the results of enhanced short-circuit current density, open circuit voltage and filling factor.

High‐performance counter electrode based on nitrogen‐doped porous carbon nanoribbons for quantum dot‐sensitized solar cells

Nitrogen-doped porous carbon nanoribbons (NPCNs) are facilely prepared by carbonization of polypyrrole (PPy) nanotubes followed by a chemical activation process. NPCN counter electrodes are subsequently fabricated by depositing NPCNs onto Ti mesh for quantum dot-sensitized solar cells (QDSCs). Electrochemical tests are carried out to evaluate the electrocatalytic performance of obtained NPCN electrode. The data of electrochemical tests suggest that the NPCN electrode has a superior electrocatalytic ability towards polysulfide (S22−/S2−) electrolyte regeneration reaction and displays a high stability in polysulfide electrolyte. The excellent electrocatalytic performance of NPCN electrode can be ascribed to their large surface area, 2D porous nanoribbon morphology, and nitrogen atom doping, which provides abundant electrocatalytic active sites and facilitates the electrolyte diffusion. Consequently, a power conversion efficiency of 3.27% is obtained by using NPCN electrode as the counter electrode for QDSC. This efficiency is close to the QDSC assembled with commonly used PbS electrode (4.0%).

Cu2S decorated MoSe2 nanosheets as counter electrode for quantum dot sensitized solar cells

The power conversion efficiency of quantum dot sensitized solar cells (QDSCs) is limited by poor redox activity of the sulfide/polysulfide electrolyte toward the counter electrodes. Here, we demonstrate the use of MoSe2-Cu2S nanoheterostructures as an efficient counter electrode in QDSCs. The QDSC based on MoSe2-Cu2S counter electrode displays an efficiency of 3.6%, which is ∼17% higher as compared to Cu2S counter electrode. The improvement is resulting from the efficient shuttling of charge carriers across the two dimensional network of MoSe2 nanosheets owing to the decrease of charge transfer resistance.

A new insight into solar paint concept: regeneration of CuS nanoparticles for paintable counter electrodes in QDSSCs

Copper sulfide (CuS) counter electrodes (CEs) fabricated by chemical bath deposition (CBD) are commonly employed CEs in quantum-dot-sensitized solar cells (QDSSCs). This article focuses on regenerating crystalline CuS nanoparticles (NPs) from residual solution of CBD and then utilizing them for paintable CEs. Our strategy eliminates the underuse of CuS NPs in conventional CBD and provides a simplistic and economically viable approach to develop efficient CEs from regenerated CuS NPs. Affirmatively, we transformed regenerated CuS NPs into paint with and without binder to make CEs having substantial electrochemical performance. Such paintable CEs revitalize the concept of a solar paint that was previously limited to photoanodes only. While demonstrating the feasibility of paintable CEs, we also prepared CEs via spin coating and drop casting using the same regenerated CuS NPs to draw a comparison with originally produced CE from CBD. The higher surface roughness, homogeneous porosity, and hydrophilicity offered by the CE prepared by paint without binder made it electrochemically more active with least charge transfer resistance (Rct), and hence, a significant power conversion efficiency of ~ 0.7% was obtained for a QDSSC having painted photoanode as well as CE.

In suit growth of CuSe nanoparticles on MXene (Ti3C2) nanosheets as an efficient counter electrode for quantum dot-sensitized solar cells

This paper reports a one-step hydrothermal method of in-situ growing copper selenide (CuSe) nanoparticles on the 2D materials-MXene (Ti3C2) nanosheets to form CuSe/Ti3C2 composite with three-dimensional structure. The CuSe/Ti3C2 slurry prepared via a solvothermal method was screen-printied onto graphite sheet to form a counter electrode (CE) in quantum dot-sensitized solar cells (QDSCs). The CuSe/Ti3C2 CE shows the better electrical conductivity for electron transfer, and a larger specific surface area to provide more active sites for polysulfide electrolyte reduction, as compared to the pristine CuSe CE and Ti3C2 CE. Hence, the device with CuSe/Ti3C2-30 mg CE achieves an efficiencies of 5.12%, which much better than that of CuSe CE (3.47%) and Ti3C2 CE (2.04%). The symmetrical dummy cells consisting of two CEs are further designed to confirm the best electrocatalytic activity and the excellent stability of composite CE towards polysulfide electrolyte. Therefore, CuSe/Ti3C2 is very promising as CE for QDSCs and this strategy provides a facile route for the design of the composite with MXene as a CE for QDSCs.

Optimizing multi-walled carbon nanotubes as a low-cost and highly electrocatalytic counter electrode for QDSCs

The development of multi-wall carbon nanotubes (MWCNTs) counter electrodes (CEs) is limited due to its poor electrocatalytic activity in quantum dot sensitized solar cells (QDSCs). In this work, nanographite and CuS quantum dots (QDs) are introduced into acid-treated MWCNTs to form 3D structural composite CE for the purpose of improving the catalytic activity. The morphology and microstructure of CEs are observed with SEM and TEM images. Either the introduced nanographite or CuS QDs have attached to MWCNTs, which makes composite CE in the higher specific surface area. The electrical property and catalytic activity of CEs is analyzed through EIS and Tafel curves. The result shows that catalytic activity of MWCNTs CEs can be optimized through introducing either nanographite or CuS QDs to increase active sites. And the catalytic activity of nanographite-based CE is worse than that of CuS QDs-based one, whose performance is close to that of Pt CE in QDSCs. The photovoltaic parameters of QDSCs based on different CEs are investigated through J-V curves. Even if the power conversion efficiency (PCE) of QDSCs with the Pt CE is slightly higher than that of MWCNTs composite, the short circuit current density of cell with nanographite/MWCNTs composite CEs (10.510 mA cm−2) is higher than that of Pt CE (10.222 mA cm−2) and the open-circuit voltage of cell of CuS QDs/MWCNTs CEs (0.874 V) is higher than that of Pt CE (0.756 V). CuS QDs/MWCNTs composite can substitute Pt material commercially as a low-cost and high efficient CEs in QDSCs.

Zeolitic-imidazolate frameworks derived Pt-free counter electrodes for high-performance quantum dot-sensitized solar cells.

Zeolitic-imidazole frameworks (ZIFs), as novel porous materials, are attracting much attention in several fields due to their special advantages such as large specific surface area, versatile porosity and well-connected networks. Here, we develop a porous ZIF-derived catalytic thin film, which was coated on the conducting glass as a counter electrode (CE) to substitute costly platinum for quantum dot-sensitized solar cells (QDSSCs). A ZIF layer is first prepared by coating ZIF-67 powders on the conducting glass, followed by the careful calcination treatments in sulfur vapour (sulfuration) or nitrogen gas (carbonization). The structure and morphologies of the derived porous film are characterized by the measurements of XRD, SEM and BET, and the electrochemical properties in the polysulfide solution are evaluated by the measurements of Tafel curves and electrochemical impedance spectroscopies. The derived porous film is used as a CE to fabricate QDSSC with CdSe quantum dot-sensitized TiO2 nanocrystalline thin film and the polysulfide solution. Compared with the photovoltaic performance of CdSe QDSSCs based on the CE prepared by the different sulfuration conditions, QDSSC based on the CE derived by the sulfuration for 30 min shows an excellent light-to-electric conversion efficiency of 3.77%, it is even higher than that of QDSSC based on Pt CE (2.98%). This work will open a new avenue to design a facile, low-cost and renewable CE for QDSSC.

A simple chemical route to synthesis the CuSe and CuS counter electrodes for titanium oxide based quantum dot solar cells

This study reveal a simple chemical route method for preparation of low cost copper selenide (CuSe) and copper sulphide (CuS) films which are used as counter electrode in quantum dot sensitized solar cells (QDSSCs). This work investigate the improvement in efficiency of Titania based QDSSCs using CuSe and CuS counter electrode. CuSe counter electrode based QDSSCs exhibit power efficiency (ɳ) of 1.68% which is higher than the 1.38% efficiency of CuS and 0.69% efficiency of Platinum (Pt) counter electrode. The improvement in efficiency of QDSSCs with CuSe counter electrode was mainly due to the low charge transfer resistance at the counter electrode–electrolyte interface. Electrochemical impedance spectroscopy (EIS) study the electron transport in the device at various interfaces. CuSe counter electrode has shown more electrocatalytic response for the reduction of redox species of the electrolyte than CuS and Pt counter electrode. Therefore CuSe counter electrode regarded as a promising alternative to the CuS and Pt counter electrode in QDSSCs.

Graphene/CuS/PbS nanocomposite as an effective counter electrode for quantum dot sensitized solar cells

In this paper, we introduce graphene/CuS/PbS nanocomposite as an effective counter electrode (CE) for quantum dot sensitized solar cells (QDSCs). The result indicated that the catalytic performance of CuS/PbS CEs was enhanced by pre deposition of graphene (G) sheets on the fluorine doped tin oxide (FTO) coated glass substrates. Here, various CEs are made by the simple successive ionic layer adsorption and reaction (SILAR) method. The result indicates that the fill factor of the cells with FTO/G/CuS/PbS CEs enhances in compare with the FTO/CuS/PbS CEs. Here, for the CdS/CdSe QD sensitized cells and G/CuS/PbS CEs, the cells' efficiency and fill factor is obtained 3.21% and 0.51 respectively which is enhanced compared to the CuS/PbS CEs with 2.54% efficiency and 0.36 fill factor. The present results indicate that the compact structure of the CuS/PbS CEs, replaces with a porous structure after graphene pre deposition which is expected to enhance the electrolyte/CE interface and consequently the fill factor. According to the obtained results, in spite of the poor catalytic activity of the graphene in the polysulfide electrolyte, it simply modifies the morphology of the CuS/PbS CEs for enhancing their performance. The results also demonstrated that G pre deposition can be systematically applied to enhance the performance of CEs in QDSCs.

Electrochemical growth of NiS nanoparticle thin film as counter electrode for quantum dot-sensitized solar cells

Abstract 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 2 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.

Graphitic porous carbon derived from human hair as ‘green’ counter electrode in quantum dot sensitized solar cells

One of the challenging issues in quantum dot sensitized solar cells (QDSCs) is to develop robust and green counter electrodes (CEs) that can replace the transition metal chalcogenides which frequently poison the photoanode during device operation. Herein, electrochemically active graphitic porous carbon (GPC), synthesized on a large scale from human hair bio-waste was successfully applied as a highly efficient, low-cost and metal-free CE in QDSC for the very first time. The GPC has uniformly distributed mesopores and graphitic edge sites which facilitate better electrolyte diffusion and charge transfer processes across the electrode/electrolyte interface. The synergistic effect of porosity and structurally ordered graphitic domains on the overall electrocatalytic performance was rationalized through variables such as carbonization time and temperature. Proof of concept QDSCs based on CdS/CdSe co-sensitized TiO2 photoanode and GPC CE registered impressive power conversion efficiencies (PCE) superior to commercial activated charcoal (AC) CE and comparable to the commonly used CEs composed of transition metal chalcogenide, CuxS.

Synthesis of novel Cu2S nanohusks as high performance counter electrode for CdS/CdSe sensitized solar cell

An important component of quantum dot sensitized solar cells (QDSSC) is the counter electrode which mediates the regeneration of oxidized quantum dots by reducing the polysulphide electrolyte. However, design and synthesis of an efficient counter electrode material is a challenging task. Herein, we report the synthesis of a unique Cu2S nanohusks directly on FTO coated glass substrates by electrodeposition and used as a counter electrode in QDSSC. When these electrodes are used for the reduction of polysulfide electrolyte in QDSSC, they exhibit higher catalytic activity and photovoltaic performance as compared to the Platinum counter electrode. The power conversion efficiency of about 4.68% has been achieved by optimizing the deposition time of Cu2S.

A Player Often Neglected: Electrochemical Comprehensive Analysis of Counter Electrodes for Quantum Dot Solar Cells.

The role played by the counter electrode (CE) in quantum dot sensitized solar cells (QDSSCs) is crucial: it is indeed responsible for catalyzing the regeneration of the redox electrolyte after its action to take back the oxidized light harvesters to the ground state, thus keeping the device active and stable. The activity of CE is moreover directly related to the fill factor and short circuit current through the resistance of the interface electrode-electrolyte that affects the series resistance of the cell. Despite that, too few efforts have been devoted to a comprehensive analysis of this important device component. In this work we combine an extensive electrochemical characterization of the most common materials exploited as CEs in QDSSCs (namely, Pt, Au, Cu2S obtained by brass treatment, and Cu2S deposited on conducting glass via spray) with a detailed characterization of their surface composition and morphology, aimed at systematically defining the relationship between their nature and electrocatalytic activity.

Facile fabrication of highly efficient carbon nanotube thin film replacing CuS counter electrode with enhanced photovoltaic performance in quantum dot-sensitized solar cells

An ideal counter electrode (CE), with high electrocatalytic activity, high performance stability, cost-efficient and applicable fabrication simplicity, is necessary to give full play to the advantages of quantum dot-sensitized solar cells (QDSSCs). Herein, we report a facile one-step preparation for carbon nanotubes (CNTs) have been explored as an electrocatalyst and low-cost alternative to platinum (Pt) and cuprous sulfide (CuS) CEs for polysulfide reduction in QDSSCs. QDSSC using this newly prepared CNT as a CE achieves a higher power conversion efficiency of 4.67% than those with a CuS (3.67%) or Pt CE (1.56%). Besides, a preliminary stability test reveals that the new CNT CE exhibits good stability. The results of Tafel polarization and electrochemical impedance spectroscopy measurements revealed that the CNTs had higher electrocatalytic activity for the polysulfide redox reaction and a smaller charge transfer resistance (8.61 Ω) at the CE/electrolyte interface than the CuS (21.87 Ω) and Pt (54.99 Ω) CEs. These results indicate that the CNT CE has superior electrocatalytic activity and can potentially replace CuS and Pt as CEs in QDSSCs. The preparation method of the CNT CE is simple and shows much promise as an efficient, stable, cost-effective and environmentally friendly CE for QDSSCs.

Low-cost solution processed nano millet like structure CoS2 film superior to pt as counter electrode for quantum dot sensitized solar cells

Cobalt Sulfide (CoS2) counter electrodes (CE) with uniform size distribution were obtained on fluorine-doped tin oxide (FTO) substrate as counter electrodes for polysulfide redox electrolyte in CdS/CdSe/ ZnS quantum dot-sensitized solar cells (QDSSCs) by chemical bath deposition (CBD) technique. In this study, we optimized the cobalt source, deposition temperature and time in the preparation of CoS2 thin film to achieve greater conversion efficiency with strong adhesion on FTO. Relative to the platinum (Pt) electrodes, the CoS2 electrode shows a higher catalytic activity, faster electron transport and lower chargetransfer resistance, which can play a role in rendering higher power conversion efficiency. As a result, QDSSCs with the optimized CoS2 CE achieved a higher short-circuit current density of 13.08 mA cm-2, open-circuit voltage of 0.47 V, fill factor of 0.34 and overall photovoltaic conversion efficiency of 2.17% obtained under one sun illumination (100 mW cm-2). Therefore, CoS2 CE can be used as a promising CE in QDSSCs with efficiency exceeding that of high-cost Pt-based cells (1.64%). Open image in new window

Copper selenide as a new counter electrode for zinc oxide nanorod based quantum dot solar cells

This work investigates the improvement in efficiency of quantum dot sensitized solar cells (QDSSCs) using copper selenide (Cu2Se) as a new counter electrode. Cu2Se counter-based QDSSC exhibits power conversion efficiency (η) of 2.28%, which is higher than the 1.17% efficiency of copper sulfide (CuS) counter electrode. Electrochemical impedance spectroscopy results show that by the changing counter electrode from CuS to Cu2Se, the charge transfer resistance at the counter electrode/electrolyte interfaces is reduced and, consequently, causes current density rise from 6.02mA/cm2 to 11.26mA/cm2. Also, open circuit voltage decay and dark current density–voltage results show that the lifetime of electron in the Cu2Se counter-based QDSSC is higher than that of QDSSC with CuS counter electrode. Therefore, Cu2Se counter electrode can be regarded as a promising alternative to the noble CuS counter electrode in QDSSCs.

ZnO/PbS core/shell nanorod arrays as efficient counter electrode for quantum dot-sensitized solar cells

To improve the electrochemical catalytic activity of the counter electrode (CE) to polysulfide electrolyte that commonly applied in quantum dot-sensitized solar cells (QDSSC), combination of catalysts with nanostructured materials is equally important as it is in the case of photoanodes. Here, we design and fabricate a new catalytic electrodes by combining PbS nanoparticles catalyst with ZnO nanorods arrays (NRs) for use as CEs in QDSSC. The ZnO/PbS core/shell CEs are prepared via the combination of chemical bath deposition and successive ionic layer adsorption and reaction methods. Compared with planar CEs, the ZnO NRs framework presents larger surface area for loading more PbS catalysts and easy accessibility of electrolyte. Additionally, the ZnO NRs core offers an excellent electron pathway for shuttling electrons to highly catalytic PbS sites due to the high electrical conductivity of ZnO nanorods. Therefore, the ZnO/PbS composite CEs exhibit much higher catalytic activity for polysulfide electrolyte than conventional Pt CE. As a result, the power conversion efficiency of QDSSC with the optimized ZnO/PbS CEs increase by nearly 120% and 78% compared to that with planar Pt and bare PbS CE, respectively.

Novel single pot synthesis of metal (Pb, Cu, Co) sulfide nanomaterials -Towards a quest for paintable electrode materials that supersedes Pt electrode

Novel single pot selective stoichiometric synthesis of cobalt, copper and lead sulfide nanomaterials has been carried out in an energy and time efficient manner by using combustion synthesis for the first time without using surfactants, capping agents and inert atmospheric conditions. X-ray diffraction and transmission electron microscope revealed the formation of respective nanocrystalline metal sulfides with different stoichiometry, whereas, electrochemical impedance analyses confirmed the low charge transfer resistance of all metal sulfide counter electrodes when compared to the Pt counter electrode, indicating their potential to be used as electrode materials. The efficiency of metal sulfide counter electrodes was tested in quantum dot sensitized solar cells (QDSSC) by applying the metal sulfide paint on fluorine doped tin oxide (FTO) plates. Current-voltage characteristics ratified the solar conversion efficiencies of 0.85, 1.3, 0.91 and 0.25, respectively for PbS (2), CuS (3), CoS (2) and Pt counter electrodes with CdS/TiO2 (1:1) working electrode and Na2S electrolyte. Thus the present study furnishes a novel method for the synthesis of metal sulfides as efficient paintable counter electrodes that can overcome Pt as counter electrode in QDSSC.

Facile pyrolytic synthesis of copper zinc tin sulfide thin films for efficient counter electrodes in quantum dot sensitized solar cells

Facile pyrolytic synthesis of copper zinc thin sulfide (Cu2ZnSnS4) thin films are first introduced into quantum dot sensitized solar cells (QDSCs) for the counter electrode. The pore size of the pyrolytic synthesis Cu2ZnSnS4 thin films is from 100nm to 300nm, and its charge transfer resistance is 37.10Ω. The assembled QDSCs with the pyrolytic synthesis Cu2ZnSnS4 thin films give short circuit photocurrent density (Jsc) of 13.33mAcm−2, open circuit voltage (Voc) of 0.52V, and fill factor (FF) of 0.45, corresponding to the photoelectric conversion efficiency (η) of 3.14%, while the QDSCs with platinized conducting glass give Jsc of 13.38mAcm−2, Voc of 0.51V, and FF of 0.34, corresponding to the η of 2.32%. Because the pyrolysis procedure is a facile, low cost and vacuum-free process, and has the advantage of obtaining various porous microstructure thin films and allowing deposition over large areas, the pyrolytic synthesis Cu2ZnSnS4 thin films can be a promise alternative to the noble Pt counter electrode in QDSCs.

Quantum dot-sensitized solar cells incorporating nanomaterials

Quantum dot-sensitized solar cells (QDSSCs) are interesting energy devices because of their (i) impressive ability to harvest sunlight and generate multiple electron/hole pairs, (ii) ease of fabrication, and (iii) low cost. The power conversion efficiencies (η) of most QDSSCs (typically <4%) are, however, less than those (up to 12%) of dye-sensitized solar cells, mainly because of narrow absorption ranges and charge recombination occurring at the QD-electrolyte and TiO(2)-electrolyte interfaces. To further increase the values of η of QDSSCs, it will be necessary to develop new types of working electrodes, sensitizers, counter electrodes and electrolytes. This Feature Article describes the nanomaterials that have been used recently as electronic conductors, sensitizers and counter electrodes in QDSSCs. The nature, size, morphology and quantity of these nanomaterials all play important roles affecting the efficiencies of electron injection and light harvesting. We discuss the behavior of several important types of semiconductor nanomaterials (sensitizers, including CdS, Ag(2)S, CdSe, CdTe, CdHgTe, InAs and PbS) and nanomaterials (notably TiO(2), ZnO and carbon-based species) that have been developed to improve the electron transport efficiency of QDSSCs. We point out the preparation of new generations of nanomaterials for QDSSCs and the types of electrolytes, particularly iodide/triiodide electrolytes (I(-)/I(3)(-)), polysulfide electrolytes (S(2-)/S(x)(2-)), and cobalt redox couples ([Co(o-phen)(3)(2+)/(3+)]), that improve their lifetimes. With advances in nanotechnology, we foresee significant improvements in the efficiency (η > 6%) and durability (>3000 h) of QDSSCs.