Search

• Composite MXene/CoS based CE is first time used in QDSSCs. • The novel MXene/CoS CE shows better charge transfer and catalytic properties.. • The QDSSC with MXene/CoS CE exhibit a high efficiency of 8.09%. • A better photovoltaic performance than most of reported similar composite CEs. Low electrocatalytic activity and/or high charge transfer resistance of counter electrodes (CEs) in quantum-dot-sensitized solar cells (QDSSCs) are the main reasons for the low photovoltaic performance. Herein, the CoS nanoparticles are anchored on the MXene (Ti 3 C 2 T x) via a simple in-situ hydrothermal reaction process. It is the first attempt to use the MXene/CoS as a highly electrocatalytic CE for QDSSCs. The QDSSCs with a MXene/CoS CE shows a significant enhancement in cell performances and yields a promising power conversion efficiency (PCE) of 8.09% compared with that of the QDSSCs with bare CoS (5.77%) and bare MXene (4.25%) CEs. The significant enhancement of PCE value is mainly attributed to the synergistic effects of the unique layered morphology of conductive MXene nanosheets and its cocatalysis with CoS nanoparticles. The coupling of layered MXene with small CoS nanoparticles (~15 nm) provides abundant catalytic active sites. The improved mesoporous morphology contributes a high specific surface area and fast electron transfer channels for S x 2− reduction. Consequently, the MXene/CoS nanocomposite can be utilized as an effective agent to boost up the photovoltaic performance of QDSSCs. [ABSTRACT FROM AUTHOR]

Highlights • The p-type CuS thin film exhibits high electrical conductivity. • CuS acts a hole transporting layer (HTL) facilitating smooth transfer of hole. • After introducing a HTL, the PCE improved by 55% with 0.6% PCE for TiO 2 /Bi 2 S 3 (4)/CuS. Abstract To search a viable way to enhance the photoconversion efficiency (PCE) of Quantum dot-sensitized solar cells (QDSSCs), we have designed a method of introducing a hole transporting layer (HTL) of p-type CuS to form the TiO 2 /Bi 2 S 3 /CuS composite electrodes. The morphology, crystal structure, optical properties and PEC performance of TiO 2 /Bi 2 S 3 /CuS composite electrodes were investigated in detail. The results showed that the photocurrent density of TiO 2 /Bi 2 S 3 /CuS was eight times higher than that of single TiO 2 and 1.51 times higher than that of TiO 2 /Bi 2 S 3 NRs. Therefore, this study provides helpful insights into rational design and fabrication of novel and efficient method for improving PEC performance of the QDSSCs. [ABSTRACT FROM AUTHOR]

Abstract In present work, Au nanoparticle-decorated TiO 2 nanorod array composite structure is designed and fabricated as the working electrode of CdS sensitized quantum dot-sensitized solar cells (QDSSCs). The results reveal that the intensity and range of sunlight absorption, photo-generated carriers transport efficiency and overall photoelectric conversion efficiency (PCE) were significantly enhanced due to followed reasons: Hot electrons of Au NPs excited by plasmon effect can offer extra electrons; plasmonic effect can contribute to the extraction and separation of light-generated electrons; the deposition of Au nanoparticles could effectively optimize the interface between TiO 2 nanorod and CdS QDs. As a result, an overall PCE of 3.29% has been obtained, which shows 19.6% enhancement compared with pure TiO 2 nanorod photoanode. Graphical abstract In present work, we developed a strategy to improve the performance of quantum dot-sensitized solar cells (QDSSCs) by using Au nanoparticle-decorated TiO 2 nanorod array as scaffold of photoanode. Image 1025 Highlights • A facile strategy was developed to prepare Au nanoparticle-decorated TiO 2 nanorod composite structure for efficient QDSSCs. • The Au nanoparticles are used to introduce plasmonic effect into photoanode. • Au nanoparticles are used to introduce plasmonic effect into photoanode. [ABSTRACT FROM AUTHOR]

Abstract A novel bidirectional (up and down)-conversion luminescence agent (GdBO 3 :Yb3+/Tb3+), that can convert ultraviolet lights and near-infrared lights into visible lights, is employed to enhance the light capture capability of CdSe 0.4 S 0.6 quantum dot-sensitized solar cells (QDSSCs). In this study, the GdBO 3 :Yb3+/Tb3+@TiO 2 photoanode is fabricated by sol-gel drop-coating method. And then, the CdSe 0.4 S 0.6 quantum dots (QDs) are deposited on the prepared photoanode surface by successive ionic layer adsorption and reaction (SILAR) technique at room temperature. The photoelectric measurements show that the light capture capability of the CdSe 0.4 S 0.6 QDSSCs device can be obviously enhanced after adding GdBO 3 :Yb3+/Tb3+ nanoparticles and the CdSe 0.4 S 0.6 /GdBO 3 :Yb3+/Tb3+@TiO 2 photoanode with 1.0% adding amount of GdBO 3 :Yb3+/Tb3+ displays the highest photovoltaic performance. The presence of GdBO 3 :Yb3+/Tb3+ nanoparticles makes CdSe 0.4 S 0.6 QDs indirectly utilize ultraviolet lights and near-infrared lights in solar lights. In addition, the scattering effect of GdBO 3 :Yb3+/Tb3+ nanoparticles in TiO 2 films can cause the reflection of the incident lights. The reflected lights can also be absorbed by the CdSe 0.4 S 0.6 QDs, increasing light capture capability. The research results demonstrate a potential applied value of bidirectional (up and down)-conversion luminescence agent in QDSSCs. Graphical abstract A novel bidirectional (up and down)-conversion luminescence agent (GdBO 3 :Yb3+/Tb3+), that can convert ultraviolet light and near-infrared light into visible light, is employed to improve the light capture capability of CdSe 0.4 S 0.6 quantum dot-sensitized solar cells (QDSSCs). The photoelectric measurements show that the light capture capability of the CdSe 0.4 S 0.6 QDSSCs devices can be obviously enhanced after adding GdBO 3 :Yb3+/Tb3+ nanoparticles and the CdSe 0.4 S 0.6 /GdBO 3 :Yb3+/Tb3+@TiO 2 photoanode with 1.0% adding amount of GdBO 3 :Yb3+/Tb3+ displays the highest photovoltaic performance. The presence of GdBO 3 :Yb3+/Tb3+ nanoparticles make CdSe 0.4 S 0.6 QDs indirectly utilize ultraviolet light and near-infrared light in solar light. In addition, the scattering effect of GdBO 3 :Yb3+/Tb3+ nanoparticles in TiO 2 films can cause the reflection of the incident light, which can be absorbed by the CdSe 0.4 S 0.6 QDs and also conduce to the increase of light capture capability. The research results demonstrate a potential of bidirectional (up and down)-conversion luminescence agent in QDSSCs. Image 1 Highlights • Bidirectional (up and down)-conversion luminescent agent is used in QDSSCs firstly. • GdBO 3 :Yb3+/Tb3+ can enhance the light capture capability of QDSSCs. • GdBO 3 :Yb3+/Tb3+ in photoanode have the function of scattering incident light. • Emitted light of GdBO 3 :Yb3+/Tb3+ locate in light absorption range of CdSe 0.4 S 0.6. [ABSTRACT FROM AUTHOR]

Polymer nano-composite composed of poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) and TiO 2 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 0.56 V of V OC , 12.24 mA cm −2 of J SC , 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%). [ABSTRACT FROM AUTHOR]

In the present work, {001}-faceted TiO 2 nanosheets were prepared via a one-step hydrothermal method and used as backbone scaffold of photoanodes of solar cells. The graphitic carbon nitride (g-C 3 N 4 ) was obtained by simple solid-state heat treatment and applied to modify the {001}-faceted TiO 2 nanosheet photoanodes. Compared with the photoanodes prepared from pure {001}-faceted TiO 2 nanosheets, the power conversion efficiency (PCE) of g-C 3 N 4 modified {001}-faceted TiO 2 nanosheet photoanodes was enhanced due to the suitable band-alignment between g-C 3 N 4 and TiO 2 . With 20% loading of g-C 3 N 4 in the photoanode, a maximum PCE of 4.23% with an open circuit voltage of 0.58 V, a short circuit current density of 15.5 mA/cm 2 , and a fill factor (FF) of 0.48 was achieved, giving 24.7% enhancement in the cell efficiency. Various characterizations were performed to understand the role of g-C 3 N 4 on the device performance, and the mechanisms that account for the improvement are suggested. [ABSTRACT FROM AUTHOR]

Herein, a TiO 2 nanoparticle/nanorod composite architecture was suggested for improving performance of quantum dot sensitized solar cells (QDSSCs), which was fabricated on transparent conductive glass substrates (FTO) via hydrothermal method followed by spin-coating, and further used as photoanode of QDSSCs. Compared with the TiO 2 nanorod photoanode, the power conversion efficiency (PCE) of the QDSSCs with this architecture was obviously improved. The champion efficiency of 4.42% was achieved, showing a 33.5% enhancement in PCE. The improved PCE mainly resulted from the increase of J sc , which increased from 9.80 (nanorod architecture) to 15.48 mA/cm 2 (nanoparticle/nanorod composite architecture). The advantages of the composite structure photoanode consist in the superior light scattering capability, faster electron transport and increased photogenerated electron concentration. [ABSTRACT FROM AUTHOR]

We report on the interfacial passivation mechanism in CdSe quantum dot-sensitized ZnO nanocrystalline thin film, where different sulfide semiconductors (such as ZnS and CdS) and sulfide ions are used to modify ZnO nanocrystalline thin film before deposition of CdSe quantum dots (QDs). It is noticed that the highest light-to-electric conversion efficiency of CdSe quantum dot-sensitized ZnO nanocrystalline thin film solar cell is attained up to 4.18 % after CdS interfacial modification. Meanwhile, a simple treatment of ZnO nanocrystalline thin film in NaS solution can also increase the conversion efficiency of CdSe quantum dot-sensitized solar cell up to 3.45 %. The electron transfer and recombination processes occurred in the interface of QD-sensitized nanocrystalline thin films with and without the different interfacial modifications are detected by measuring intensity modulated photovoltage spectroscopy and electrochemical impedance spectroscopy of solar cells. These results indicate that adsorption of S ions on the surface active sites of ZnO nanoparticles is the main reason for the conversion efficiency improvement due to the interfacial passivation of sulfide semiconductors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Black rutile TiO 2 nanoparticles (NPs) is fabricated by fs laser filament processing. • CdS/CdSe quantum dot sensitized solar cells (QDSSCs) with black TiO 2 -NPs are assembled. • A power conversion efficiency of 9.1 % in QDSSCs is achieved. • The increase in PCE is ascribed to the formed amorphous shell on the surface of TiO 2 -NPs. The research deals with fabrication of CdS/CdSe-sensitized quantum dot sensitized solar cells (QDSSCs) with laser-engineered black rutile TiO 2 nanoparticles (TiO 2 -NPs) as the photoanode material. Three QDSSC devices with pristine and two types of black rutile TiO 2 -NPs engineered respectively in water and ethanol by intense femtosecond laser propagating in the filamentation regime were prepared in the same architecture. Extremely different power conversion efficiencies (PCE) of 1.43 %, 3.68 % and 9.11 %, in which the black TiO 2 -NPs-based devices show respectively a two-fold and six-fold PCE higher than the pristine TiO 2 -NPs, were obtained. The absorption and electrochemical impedance spectroscopy analyses revealed that the device with the highest PCE has the highest absorption efficiency in the wide spectral range from UV to mid-infrared and shunt resistance (R sh) of 1364.9 Ω, but the smallest series resistance (R s) of 190.3 Ω, which are attributed to the surface modification on the structural and optical properties of TiO 2 -NPs by femtosecond laser pulses. [ABSTRACT FROM AUTHOR]

TiO 2 nanoparticles are typically employed to construct the porous films for quantum dot-sensitized solar cells (QDSCs). However, undesirable interface charge recombination at grain boundaries would hinder the efficient electron transport to the conducting substrate, giving rise to the decline of open-circuit voltage ( V oc ). In this work, vertically aligned architectures of oriented one-dimensional (1D) TiO 2 nanorod arrays hydrothermally grown on substrates pave a way in designing highly efficient QDSCs with efficient radial-directional charge transport. SEM, TEM, XRD, and Raman spectroscopy were employed to characterize the as-prepared TiO 2 nanorods, showing the rutile phase with single-crystalline structure. The homogeneous deposition of CdS/CdSe QDs on the surface of TiO 2 nanorods has been achieved by in-situ grown strategies (i.e., successive ionic layer absorption and reaction, and chemical bath deposition). An extremely high V oc value up to 0.77 V has been achieved for CdS/CdSe QDSCs based on the well-ordered 1D nanorod arrays. To the best of our knowledge, it is the highest V oc reported for TiO 2 -based QDSCs. Dependencies of photovoltaic performance, optical absorption, and interfacial charge behavior on the length of nanorods were systematically investigated. A 1.7 μ m nanorod-array photoelectrode-based QDSC delivers a remarkable power conversion efficiency up to 3.57% under simulated AM 1.5 100 mW cm −2 illumination, attributed to the balance of competition between the increase of QD loading and suppression of interfacial recombination. This work highlights the combination of QDs with high absorption coefficient 1D architectures possessing efficient charge transport for constructing high efficiency solar cells. [ABSTRACT FROM AUTHOR]

Currently, most of CuS counter electrodes (CEs) used in quantum dot-sensitized solar cells (QDSSCs) are provided with a thickness of hundreds of nanometers or even several microns. Considering the CE with low thickness having many advantages, thin CuS films with thickness ranging from 47 nm below to 115 nm have been synthetized in this paper via chemical bath deposition (CBD) method with different bath concentrations. A power conversion efficiency (PCE) of 3.25% has been achieved utilizing CuS thin films a thickness of only 64 nm as CEs in QDSSCs without any structural optimization, which is higher than the value of the cell employing CuS CE with thickness of 2.8 μm. Electrochemical impedance spectroscopy, Tafel polarization, and two-point current-voltage measurements are used to investigate the electrocatalytic and conductive performance of CuS CEs with different thickness. Owing to the highest electrocatalytic capacity and good conductivity of the 64 nm-thick CuS CE, QDSSC assembled with this CE has reached relatively high PCE under one sun illumination (100 mW cm −2 , AM 1.5). In addition, cyclic voltammetry measurements indicate that the thin CuS CE has a good stability against the polysulfide electrolyte. [ABSTRACT FROM AUTHOR]

A low-cost, stable and efficient FeS thin film counter electrode (CE) was fabricated for quantum dot-sensitized solar cells (QDSSCs) by a facile chemical bath deposition method using different acidic hydroxyl solvents (ethanol, isopropanol, and tert-butanol) and triethanolamine. The choice of solvents greatly affected the surface morphology and thickness of FeS CEs. Apart from surface morphology, the increase in the atomic percentage of sulfur in tert-butanol and triethanolamine-mediated FeS also plays a crucial role in increasing the electrocatalytic activity of the CE. The QDSSC’s power conversion efficiency was 2.15%, which is attributed to the high fill factor (FF) of 0.443. The obtained PCE is far better than the previously reported value of 1.76% for FeS in QDDSC’s. Excellent stability of the photoelectric performance of the FeS CE is also demonstrated. The enhanced electrochemical performance of the interwoven FeS networks can be attributed to their unique morphology, which possesses a shorter diffusion length of the ions and easier transportation of the electrons. [ABSTRACT FROM AUTHOR]

A series of novel PbS/TiO 2 nanotubes was fabricated as counter electrodes (CEs) through a combination of anodic oxidation and successive ionic-layer adsorption and reaction methods. The photovoltaic-conversion efficiency of ZnO nanorods sensitized with CdS quantum dots using the optimized PbS(6)/TiO 2 CE increased by nearly 440.8% and 227.5% compared with the efficiency of nanorods using planar Pt and bare TiO 2 CE, respectively. Thus, the novel PbS/TiO 2 composite CE was a promising catalytic electrode with excellent electrocatalytic activity for the reduction of charge carriers in polysulfide electrolyte. [ABSTRACT FROM AUTHOR]

Copper sulfide (Cu 2 S) films were deposited on F-doped SnO 2 (FTO) substrates via the electrodeposition (ED) of copper (Cu) nanoparticles followed by sulfurization. The Cu nanoparticles were deposited on FTO substrates for various ED times ranging from 10 to 30 min at a constant −0.4 V. The FTO/Cu films consisted of flower-like nanoparticles comprised of randomly-clustering nanoflakes. The Cu nanoparticles electrodeposited for 10 min (FTO/Cu (10 min)) were dispersed sparsely over the FTO substrate, whereas the FTO/Cu (20 and 30 min) provided increased coverage. Unlike FTO/Cu 2 S (10 min), the FTO/Cu 2 S (20 and 30 min) consisted of vertically-standing large Cu 2 S nanosheets with numerous small nanosheets in between. This was attributed to the sufficient number of Cu seed nanoflakes, which not only facilitate ion transport of the redox couple but also increased the surface area, leading to significantly enhanced electrocatalytic activity. The quantum dot-sensitized solar cell (QD-SSC) with FTO/Cu 2 S (20 min) exhibited a significantly improved cell efficiency of 4.58%, compared to those with Pt and FTO/Cu 2 S (10 min). The QD-SSC with the FTO/Cu 2 S (30 min) showed similar cell efficiency to that with the FTO/Cu 2 S (20 min), despite the larger surface area because of its amorphous crystallographic structure offsetting the electrocatalytic activity. [ABSTRACT FROM AUTHOR]

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 Cu 2 S 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 Cu 2 S. [ABSTRACT FROM AUTHOR]

Yttrium-doped ZnO nanorod arrays were applied to photoanodes of quantum dot-sensitized solar cells (QDSCs). The introduction of yttrium to ZnO nanostructures facilitates the growth of ZnO nanorods and increases the amount of QD deposition with a large surface area. Furthermore, lower electrical resistance and longer electron lifetime were achieved with yttrium-doping owing to fewer defects and trap sites on the surface of yttrium-doped ZnO nanorods. As a result, the conversion efficiency of 3.3% was achieved with the optimized concentration of yttrium. [ABSTRACT FROM AUTHOR]

Pursuit of an efficient strategy for quantum dot-sensitized photoanode has been a persistent objective for enhancing photovoltaic performances of quantum dot-sensitized solar cell (QDSC). We present here the fabrication of the indium sulfide (In 2 S 3 ) quantum dot-sensitized titanium dioxide (TiO 2 ) photoanode by combining successive ionic layer adsorption and reaction (SILAR) with solvothermal processes. The resultant QDSC consists of an In 2 S 3 sensitized TiO 2 photoanode, a liquid polysulfide electrolyte, and a Co 0.85 Se counter electrode. The optimized QDSC with photoanode prepared with the help of a SILAR method at 20 deposition cycles and solvothermal method yields a maximum power conversion efficiency of 1.39%. [ABSTRACT FROM AUTHOR]

Quantum dot-sensitized solar cells ( QDSSCs) were synthesized using CdS and CdSe quantum dots ( QDs) incorporated onto one-dimensional ZnO nanorods by successive ionic layer adsorption. In order to get the highest performance of the synthesized cell, the concentration of precursor QD solution and the number of deposition cycles in the QD solution were varied together. The photovoltaic performance of each cell was compared with the ultraviolet/visible absorption spectra and incident photon to current efficiency graphs. QDSSCs incorporating single-walled carbon nanotubes ( SWNTs), sprayed onto the substrate before deposition of the next layer, exhibited enhanced or decreased photocell efficiency compared to that of the pristine cell. In particular, a maximum rate increase of 17% was obtained with the solar cell containing SWNTs in CdSe QDs. [ABSTRACT FROM AUTHOR]

Quantum dot-sensitized solar cells ( QDSSCs) were synthesized using CdS and CdSe quantum dots ( QDs) incorporated onto one-dimensional ZnO nanorods by successive ionic layer adsorption. In order to get the highest performance of the synthesized cell, the concentration of precursor QD solution and the number of deposition cycles in the QD solution were varied together. The photovoltaic performance of each cell was compared with the ultraviolet/visible absorption spectra and incident photon to current efficiency graphs. QDSSCs incorporating single-walled carbon nanotubes ( SWNTs), sprayed onto the substrate before deposition of the next layer, exhibited enhanced or decreased photocell efficiency compared to that of the pristine cell. In particular, a maximum rate increase of 17% was obtained with the solar cell containing SWNTs in CdSe QDs. [ABSTRACT FROM AUTHOR]

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 180–270 nm and film thickness of 825 nm. It also revealed superior J sc (13.87 mA/cm 2 ) 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 900 min 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 700 min, and consequently diminished by 8.27% from 700 to 900 min. [ABSTRACT FROM AUTHOR]

As an upconverter, lanthanide-doped NaYF 4 (Ln-NaYF 4 ) has been integrated into the photoanodes for quantum-dot sensitized solar cells. Compared with the solar cells with pure TiO 2 , the upconverter based solar cells exhibited a 17.6% increase in the photocurrent and a 20% increase in the power conversion efficiency. Furthermore, when the integrated Ln-NaYF 4 is pretreated by annealing, the resulting photoanode demonstrates an obvious improvement in the photocurrent generation and the power conversion efficiency due to the annealing-induced enhancement of the upconversion emission as well as the elimination of the defects allowing for efficiently reducing charge recombination. The best photovoltaic performance with a short-circuit current of 14.36 mA/cm 2 and a power conversion efficiency of 4.37% has been obtained with the solar cells containing the annealed upconverters. Both the solar cells integrated with the Ln-NaYF 4 pretreated by annealing or not demonstrate obvious photocurrent responses under the illumination of the NIR light. This finding demonstrates the feasibility of the combination of the up-converting materials with quantum dot-sensitized solar cells to extend the exploitation of the solar light to a wider range thus enabling the fabrication of highly efficient solar cells. [ABSTRACT FROM AUTHOR]

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 2 /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 −2 ). 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. [ABSTRACT FROM AUTHOR]

Vacuum thermal evaporated Cu x S (VTE-Cu x S) film on fluorine-doped tin oxide substrate has been investigated as counter electrode (CE) for quantum dot-sensitized solar cells (QDSCs) with polysulfide electrolyte. The photovoltaic parameters of QDSCs show an obvious dependence on the annealing time of Cu x S film, and the maximum power conversion efficiency of 3.16 ± 0.05% under one sun illumination (100 mW cm −2 , AM 1.5 G) was obtained when the VTE-Cu x S CE was annealed at 270 °C for 300 s (VTE-Cu x S-300s CE). Electrochemical impedance spectroscopy, Tafel polarization, and cyclic voltammetry measurements have been employed to investigate the electrocatalytic activity of VTE-Cu x S-300s CE. The electrocatalytic activity of the VTE-Cu x S-300s CE is much higher than that of Pt CE, and is slightly higher than that of Cu 2 S CE in situ prepared on brass sheet. In particular, VTE-Cu x S-300s CE holds high diffusion velocity of S 2− /S n 2− in polysulfide electrolyte, and the stability of its electrocatalytic activity in polysulfide electrolyte is better than that of Pt and Brass-Cu 2 S CEs obviously. [ABSTRACT FROM AUTHOR]

Quantum dot-sensitized solar cells (QDSCs) have been attracting much attention due to their unique characteristics such as multiple exciton generation and a tunable band gap. Supporting materials of photoelectrodes for QDSCs like TiO 2 and ZnO are some of the most important parts because they absorb sensitizers and also function as photo-injected electron pathways. Particularly, ZnO has many advantages for the photoelectrodes of QDSCs. In this study, we investigated the effect of ammonia treatment on ZnO nanoflower-based QDSCs by varying the concentration of ammonia. The influence of ammonia treatment is discussed with respect to the power conversion efficiency from the J-V curve, electrochemical impedance spectroscopy (EIS), and other analyses. [ABSTRACT FROM AUTHOR]

Mesoporous TiO 2 microspheres with large surface area are synthesized by a hydrothermal reaction of titanium glycolate, and then introduced into CdS quantum dot-sensitized solar cell (QDSC). These mesoporous TiO 2 microspheres can not only increase the adsorption amount of quantum dots (QDs), but also possess effective light scattering ability due to the proper size, in comparison with traditional TiO 2 (P25). An overall power conversion efficiency of 2.63% is achieved by using these mesoporous TiO 2 microspheres as electrode in QDSC, significantly higher than that derived from P25 TiO 2 electrode. In addition, the photovoltaic behaviors of the materials are studied by surface photovoltage measurement to explain the excellent performance of QDSCs. [ABSTRACT FROM AUTHOR]

A PbS:Hg quantum dots-sensitized solar cell (QDSC) combined with a dye-sensitized solar cell (DSC) to harvest panchromatic solar spectrum from the visible light to the near IR is demonstrated. We use the filter to split the solar energy and access the total conversion efficiency. The DSC performing 12.4% under AM1.5G sunlight was able to generate 9.1% with a short-wave pass filter cutting off photons of wavelength longer than 650 nm. On the other hand, QDSC performing 5.58% generated 3.42% with the use of a long-wave pass filter transmitting beyond 630 nm. Calculated on the basis of transmitted light, DSC and QDSC performed 24.0% and 5.90%, leading to almost 13.1% of estimated total power conversion efficiency by harvesting the solar energy from visible light to the NIR. [ABSTRACT FROM AUTHOR]

We fabricated quantum dot-sensitized solar cells (QDSSCs) using cadmium sulfide (CdS) and cadmium telluride (CdTe) quantum dots (QDs) as sensitizers. A spin coated TiO2 nanoparticle (NP) film on tin-doped indium oxide glass and sputtered Au on fluorine-doped tin oxide glass were used as photo-anode and counter electrode, respectively. CdS QDs were deposited onto the mesoporous TiO2 layer by a successive ionic layer adsorption and reaction method. Pre-synthesized CdTe QDs were deposited onto a layer of CdS QDs using a direct adsorption technique. CdS/CdTe QDSSCs had high light harvesting ability compared with CdS or CdTe QDSSCs. QDSSCs incorporating single-walled carbon nanotubes (SWNTs), sprayed onto the substrate before deposition of the next layer or mixed with TiO2 NPs, mostly exhibited enhanced photo cell efficiency compared with the pristine cell. In particular, a maximum rate increase of 24% was obtained with the solar cell containing a TiO2 layer mixed with SWNTs. [ABSTRACT FROM AUTHOR]

Abstract: CdS/CdSe quantum dot-sensitized solar cells (QDSCs) based on TiO2 nanoparticles were examined. TiO2 nanoparticles were coated with three different insulating oxide materials, Al2O3, MgO and BaTiO3, as a barrier layer to prevent recombination losses. In this study, a single and double coated barrier layer is fabricated to optimize the passivation effect. The optimized double coating structure increased the electron transport rate and electron lifetime and showed improved conversion efficiency. [Copyright &y& Elsevier]

Abstract: The Cu2ZnSnS4 (CZTS) thin films with uniform and porous surface feature with the pore size of 100-200nm were successfully prepared by pyrolysis procedure using the methanol solution containing copper chloride dihydrate (0.06mol dm−3), zinc chloride (0.03mol dm−3), stannous chloride dihydrate (0.03mol dm−3), thiourea (0.48mol dm−3) and deionized water (1.92mol dm−3) as precursor solution at 380°C in air atmosphere. Electrochemical impedance spectroscopy was applied to evaluate the electrochemical catalytic activity of the pyrolysis CZTS thin films for redox couple of Sn 2-/S2− and the charge transfer resistance was 64.08Ω using the pyrolysis CZTS thin film obtained by repeating the procedure of dipping the FTO substrate into the precursor solution and heating at 380°C for 7 cycles. The assembled quantum dot-sensitized solar cells gave an open-circuit photovoltage of 0.52V, a short-circuit photocurrent density of 12.96mAcm−2, and a fill factor of 0.38, corresponding to the photoelectric conversion efficiency of 2.56%. Because the pyrolysis procedure was a facile, low cost and vacuum-free process, and had the advantage of obtaining various porous microstructure thin films and allowing deposition over large areas, the pyrolysis CZTS thin films can serve as an effective counter electrode for QDSCs. [Copyright &y& Elsevier]

Abstract: A sandwich structural CoS/graphene sheet (CoS/GS) electrode was prepared by repeating electrophoretic deposition of graphene sheets and deposition of CoS nanoparticles. We found the graphene sheets play a key role in controlling the morphology of the nanostructure. The obtained CoS/graphene nanocomposite counter electrode has a high specific surface area and displays an excellent electrochemical activity toward the polysulfide electrolyte. Consequently, the quantum dot-sensitized solar cell based on CoS/GS counter electrode shows an improved photovoltaic performance. [Copyright &y& Elsevier]

Highlights: [•] ZnO pyramid arrays assembled by thin nanoswires are synthesized and its photovoltaic properties are investigated. [•] Performs of the CdS QDSSCs based on the ZnO nanorod arrays, nanotube arrays, forest, and pyramid arrays are compared. [•] Pyramid arrays can achieve high photoelectric performs due to its anti-reflection, high specific area and direct electron transmission channels. [Copyright &y& Elsevier]

Abstract: Quantum dots (QDs) have been attractive recently with their multiple exciton generation characteristics. QD solar cells can more effectively use the incident energy because one or more electrons are generated with the photon of high energy. They have less heat loss and higher theoretical efficiency (44%) than single exciton generation solar cells (33%). This work focused on Si as alternative to conventional QD materials. Si has QD's unique characteristics such as the quantum size effect and quantum confinement with non-toxicity and abundance. Si QDs were fabricated by the multi-hollow discharge plasma chemical vapor deposition and applied to QD-sensitized solar cells (QDSCs). Contrary to the good characteristics of Si QDs, Si QDSCs had poor performance as compared with conventional QDSCs because of the weak combination between Si QDs and TiO2. Small amounts of adsorbed Si QD on TiO2 made low photocurrent and TiO2 surface widely exposed to redox electrolyte caused charge recombination, the decrease of open-circuit voltage, and low fill factor. For improving their combination, Si QDs were functionalized. The electron transfer from Si to TiO2 and the bonding with TiO2 were improved and more Si QDs were adsorbed by the functionalization. In the functionalization process, the linking source is one of the key parameters. Therefore, 4-vinylbenzoic acid was controlled and its effect was analyzed. The change in the photovoltaic parameters according to the concentration of 4-vinylbenzoic acid and the performance dependence were investigated. In order to verify their characteristics, the effects in terms of the photovoltaic performance, electrochemical impedance, and optical properties were examined. [Copyright &y& Elsevier]

CdS/CdSe co-sensitizers on TiO2 films were annealed using a two-step procedure; high temperature (300 °C) annealing of TiO2/CdS quantum dots (QDs), followed by low temperature (150 °C) annealing after the deposition of CdSe QDs on the TiO2/CdS. For comparison, two types of films were prepared; CdS/CdSe-assembled TiO2 films conventionally annealed at a single temperature (150 or 300 °C) and non-annealed films. The 300 °C-annealed TiO2/CdS/CdSe showed severe coalescence of CdSe QDs, leading to the blocked pores and hindered ion transport. The QD-sensitized solar cell (QD-SSC) with the 150 °C-annealed TiO2/CdS/CdSe exhibited better overall energy conversion efficiency than that with the non-annealed TiO2/CdS/CdSe because the CdSe QDs annealed at a suitable temperature (150 °C) provided better light absorption over long wavelengths without the hindered ion transport. The QD-SSC using the two-step annealed TiO2/CdS/CdSe increased the cell efficiency further, compared to the QD-SSC with the 150 °C-annealed TiO2/CdS/CdSe. This is because the 300 °C-annealed, highly crystalline CdS in the two-step annealed TiO2/CdS/CdSe improved electron transport through CdS, leading to a significantly hindered recombination rate. [ABSTRACT FROM AUTHOR]

Abstract: Quantum dot-sensitized solar cell (QDSC) based on multiple exciton generation of QD has been expected to realize high efficiency. This work focused on Si QD instead of conventional QD materials because of their toxicity and scarcity. Si QDs were fabricated by multi-hollow discharge plasma chemical vapor deposition. General QDSCs use polysulfide electrolyte because it is suitable for stabilizing QDs and its redox reaction is the best as compared with other redox systems. The improvement of redox reaction which is one of the slowest reactions in the kinetic analysis is closely connected with the enhancement of performance. For the enhancement on the overall performance of Si QDSC, the performance dependence on electrolyte composition was investigated. The concentrations of Na2S and S were varied for the activation of redox reaction and KCl concentration was optimized for the improvement of electrolyte characteristics. Consequently, the best performance of Si QDSC was obtained with 1M Na2S, 2M S, and 0.4M KCl polysulfide electrolyte. [Copyright &y& Elsevier]

Abstract: Highly conductive hydrogel polysulfide electrolyte is first fabricated using dextran as gelator and used as quasi-solid-state electrolyte for quantum dot-sensitized solar cells (QDSSCs). The hydrogel electrolyte with gelator concentration of 15wt% shows almost the same conductivity as the liquid one. Moreover, its liquid state at elevated temperature allow for the well penetration into the pores in electrodeposited CdS/CdSe co-sensitized TiO2 photoanode. This gel electrolyte based QDSSC exhibits power conversion efficiency (η) of 3.23% under AG 1.5G one sun (100mWcm−2) illumination, slightly lower than that of liquid electrolyte based cell (3.69%). The dynamic electron transfer mechanism of the gel and liquid electrolyte based QDSSC are examined by electrochemical impedance spectroscopy (EIS) and controlled intensity modulated photocurrent/photovoltage spectroscopy (CIMPS/IMVS). It is found that the electron transport in gel electrolyte based cell is much faster than the liquid electrolyte based cell but it tends to recombine more easily than the latter. However, these differences fade away with increasing the light intensity, showing declining electron collection efficiency at higher light intensity illumination. As a result, a conversion efficiency of 4.58% is obtained for the gel electrolyte based quasi-solid-state QDSSC under 0.12 sun illumination. The high conductivity and the good permeation of gel electrolyte may contribute mainly to its excellent photovoltaic performance. [Copyright &y& Elsevier]

Abstract: A quantum dot-sensitized solar cell (QDSSC) is fabricated using a composite layer, consisting of ZnO nanowires and ZnO nanoparticles (CL-ZnO) as its semiconductor film. The diameter and the thickness of each ZnO nanowire (ZNW) are ∼100nm and ∼6μm, respectively. The structure and morphology of the films with ZnO nanoparticles (ZNPs), ZNWs, and CL-ZnO are characterized by X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images. Cadmium sulfide quantum dots (CdS QDs) are deposited on the ZNWs, ZNPs, and CL-ZnO by a successive ionic layer adsorption and reaction (SILAR) cycle. The highest efficiency (η) for the QDSSC sensitized by CdS (CdS-QDSSC) is obtained in the case of CL-ZnO photoanode, and this is attributed to significant improvement in the short-circuit photocurrent density (J SC) of the pertinent cell, which is 2.81- fold higher than that of the cell with ZNWs. Moreover, cadmium selenide quantum dots (CdSe QDs) are used as co-sensitizer along with the CdS QDs for the CL-ZnO semiconductor layer (film designated as CL-ZnO/CdS/CdSe), and the pertinent QDSSC showed much higher efficiency than the one obtained in the case of the cell using only CdS QDs as the sensitizer. Finally, a passivation layer of ZnS was deposited on the film of CL-ZnO/CdS/CdSe, and the cell with this film (CL-ZnO/CdS/CdSe/ZnS) showed an efficiency of 0.55%, the highest in this research. Electrochemical impedance spectra (EIS), UV–vis absorbance spectra, transmission electron microscopy (TEM), and incident photon-to-current conversion efficiency (IPCE) curves are used to substantiate the explanations. [Copyright &y& Elsevier]

AgS quantum dots were deposited on the surface of TiO nanorod arrays by a two-step photodeposition. The prepared TiO nanorod arrays as well as the AgS deposited electrodes were characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscope, suggesting a large coverage of AgS quantum dots on the ordered TiO nanorod arrays. UV-vis absorption spectra of AgS deposited electrodes show a broad absorption range of the visible light. The quantum dot-sensitized solar cells (QDSSCs) based on these electrodes were fabricated, and the photoelectrochemical properties were examined. A high photocurrent density of 10.25 mA/cm with a conversion efficiency of 0.98% at AM 1.5 solar light of 100 mW/cm was obtained with an optimal photodeposition time. The performance of the QDSSC at different incident light intensities was also investigated. The results display a better performance at a lower incident light level with a conversion efficiency of 1.25% at 47 mW/cm. [ABSTRACT FROM AUTHOR]

Abstract: ZnS overlayers were deposited on the CdS quantum dot (QD)-assembled TiO2 films, where the CdS QDs were grown on the TiO2 by repeated cycles of the in situ chemical bath deposition (CBD). With increasing the CdS CBD cycles, the CdS QD-assembled TiO2 films were transformed from the TiO2 film partially covered by small CdS QDs (Type I) to that fully covered by large CdS QDs (Type II). The ZnS overlayers significantly improved the overall energy conversion efficiency of both Types I and II. The ZnS overlayers can act as the intermediate layer and energy barrier at the interfaces. However, the dominant effects of the ZnS overlayers were different for the Types I and II. For Type I, ZnS overlayer dominantly acted as the intermediate layer between the exposed TiO2 surface and the electrolyte, leading to the suppressed recombination rate for the TiO2/electrolyte and the significantly enhanced charge-collection efficiency. On the contrary, for Type II, it dominantly acted as the efficient energy barrier at the interface between the CdS QDs and the electrolyte, leading to the hindered recombination rate from the large CdS QDs to the electrolyte and thus enhanced electron injection efficiency. [Copyright &y& Elsevier]

Abstract: The photovoltaic performance of quantum dot-sensitized solar cell (QDSSC) based on mesoscopic nitrogen-doped TiO2 spheres prepared by solvothermal method was investigated. The results indicate that CdSe x S(1−x)/CdSe QDSSC based on this mesoscopic nitrogen-doped TiO2 spheres shows an energy conversion efficiency of 3.67%, which is higher than that of the undoped TiO2 spheres (2.14%). The electrochemical impedance spectroscopy shows retards charge recombination is occurred on nitrogen-doped TiO2 spheres photoanode. The improvement of the photovoltaic performance of QDSSC could be attributed to the retarding charge recombination, the acceleration of the transfer rate of electrons, higher quantum dots loading and enhanced light scattering in the N-doped TiO2 spheres film. A higher photovoltaic performance could be expected for other QDSSC with this N-doped TiO2 sphere material. [Copyright &y& Elsevier]

Abstract: Chemically crosslinked polyacrylamide-based hydrogel has been first used as the polymer matrix to prepare quasi-solid-state polysulfide electrolyte for CdS/CdSe co-sensitized solar cells (QDSCs). The room temperature ionic conductivity of the gel electrolyte reaches 0.093S·cm−1. QDSCs based on this quasi-solid-state electrolyte can present up to 4.0% of light-to-electricity conversion efficiency. Meanwhile, the interfacial recombination at TiO2/electrolyte interface of the cell is also investigated by Electrochemical Impedance Spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

Quantum dot-sensitized solar cells based on fluorine-doped tin oxide (FTO)/Au/TiO/CdS photoanode and polysulfide electrolyte are fabricated. Au nanoparticles (NPs) as interfacial layer between FTO and TiO layer are dip-coated on FTO surface. The structure, morphology and impedance of the photoanodes and the photovoltaic performance of the cells are investigated. A power conversion efficiency of 1.62% has been obtained for FTO/Au/TiO/CdS cell, which is about 88% higher than that for FTO/TiO/CdS cell (0.86%). The easier transport of excited electron and the suppression of charge recombination in the photoanode due to the introduction of Au NP layer should be responsible for the performance enhancement of the cell. [ABSTRACT FROM AUTHOR]

This work demonstrates a straightforward strategy to develop the copper-indium-sulfide (CIS) quantum dot-sensitized solar cells (QDSSCs) consisting of ionic liquids (ILs) as electrolyte instead of any volatile solvent. The power conversion efficiency (PCE) of the solar cell yielded with 0.36% in the presence of 1-butyl-3-methylimidazolium sulfide ([BMIm][S2−/S n 2−]) as electrolyte. Furthermore, binary mixture of [BMIm][S2−/S n 2−] and 1-butyl-3-methylimidazolium thiocyanate ([BMIm][SCN]) exhibited an improvement of J SC and FF yielding with 0.75% (J SC : 8.69 mA cm−2, V OC : 0.32 V, FF 26.8%). It exhibited long-term stability within 20% drops after 72 h-continuous photo-irradiation and subsequent storage for more than 1300 h in dark. It is due to suppression of the volatilization of solvent and decomposition of sulfide/polysulfide (S2−/S n 2−) anions. The solar cell performances were found to promote as an increase of interfacial charge transfer efficiency between electrolyte and electrodes by means of electrochemical impedance spectroscopy. This work demonstrates a straightforward strategy to improve the durability of the copper-indium-sulfide (CIS) quantum dot-sensitized solar cells (QDSSCs) consisting of ionic liquids (ILs) as electrolyte instead of any volatile solvent. The binary of [BMIm][S2−/S n 2−] with [BMIm][SCN] exhibited the PCE yielding with 0.75%, and its stability was maintained within 20% drops after 72 h-continuous photo-irradiation and subsequent storage for more than 1300 h in dark. Unlabelled Image • Copper-indium-sulfide quantum dot-sensitized solar cells (QDSSCs) were fabricated. • Imidazolium ionic liquids (ILs) involving S2−/S n 2− ions were employed. • Binary of [BMIm][S2−/S n 2−] with [BMIm][SCN] exhibited high ionic conductivity. • ILs with non-volatilization makes highly stable solar cell performance. [ABSTRACT FROM AUTHOR]

A wide spectrum of light harvesting silver selenide (Ag2Se) quantum dots (QDs) with an average size of ~ 5 nm has been synthesized by a low-temperature one-pot hot injection method. To finely control the size of Ag2Se QDs, oleylamine was used as the solvent, and dodecanethiol was used as the capping agent as well as a stabilizer. The prepared Ag2Se QDs were ex situ sensitized on the porous TiO2 nanofiber (NF) substrate via a direct adsorption method to use as efficient photoanode for quantum dot-sensitized solar cell (QDSC). The UV-Vis-NIR absorption and photoluminescence studies revealed that Ag2Se QD-sensitized porous TiO2 NF photoanode (Ag2Se/P-TiO2) exhibited near-infrared (NIR) absorption and fast electron kinetics. Further, the QDSC fabricated using Ag2Se/P-TiO2 NFs as the photoanode, Cu2S as the counter electrode, and liquid polysulfide (S2−/Sx2− redox couple) as the electrolyte exhibited a photoconversion efficiency of 2.50% with an improved photocurrent density of 11.12 mA/cm2. [ABSTRACT FROM AUTHOR]

Quantum dot solar cells (QDSC) have been subject of extensive research in recent years. QDSC, as a promising alternative to existing solar cells, are among the candidates for next-generation photovoltaic devices that require low cost, high efficiency, so that quantum dots stand out for their unique features and versatile desirable on photovoltaic systems. The rapid development of QDSC provided a significant increase in energy conversion efficiency, which was certified for the first time in 2010 as 2% then being currently as 11.3%, according to the National Renewable Energy Laboratory (NREL). This paper presents a review of the quantum dot-sensitized solar cells and the major advances reported concerning these cells, besides other types of cell architectures involving quantum dots.