Quantum Dot-sensitized Solar Cells Research Articles

Charge transport in quantum dot sensitized solar cells: A mathematical model

In this paper, charge transport in quantum dot (QD) thin films is modeled by considering trap-state assisted tunneling among the QD thin films. Multiple parameters associated with traps like density, position, and capture/emission rates which can significantly affect tunneling, have been considered in the model. The model is further extended to the quantum dot sensitized solar cells (QDSSC), and the effects of tunneling rate variation in accordance with the trap-states at the QD-QD interfaces and/or in the shell of QDs is analyzed. In the proposed model, multiple silicon QD layers as active material are considered, which are sandwiched between ZnO as electron transport layer (ETL) and a MoO3 as hole transport layer (HTL). The model couples drift–diffusion framework for charge transport in ETL and HTL, and a system of rate equations for carrier dynamics among the QDs and their interfaces with ETL and HTL. Our analysis shows that the variations in trap-state concentration significantly affect the charge extraction and recombination scenario in the active layer of QDSSC, consequently producing a direct impact on device characteristics.

O, S-g-C3N4 nanotubes as photovoltaic boosters in quantum dot-sensitized all-weather solar cells: a synergistic approach for enhanced power conversion efficiency in dark-light conditions

All up-to-the-minute solar cells generate highly efficient electricity under sunlight. However, the power outputs are ∼ zero under dark conditions due to the relatively low visible light intensity. We report high-performance quantum dots-sanitized all-weather solar cells (QDSSCs). The devices were based on rationally designed carbon quantum dots (CQDs) decorated oxygen and sulfur co-doped graphitic carbon nitride nanotubes (O, S-g-C3N4 NTs)-sensitized TiO2/long-persistence phosphor (LPP) photoanodes and Pt counter electrodes (CE). O, S-doped-g-C3N4 NTs can act as photo-boosters as well as the blocking layer to prevent the backflow of photoexcited electrons and prevent their recombination with the electrolyte. LPPs can store unabsorbed light ranging from visible to infrared light across the photoanode and convert it into green fluorescence, ultimately persistent CQDs/O, S-g-C3N4 NTs irradiation, and electricity generation under sunlight illumination in all light-dark environments. The maximum PCE was 18.5% for the device 7-CC/L prepared with a composite of CQDs and O, S-g-C3N4 NTs with an optimized weight of 7 mg and 0.2 g, respectively.

Photo-supercapacitor based on quantum dot-sensitized solar cells and active carbon supercapacitors

Photo-supercapacitor based on quantum dot-sensitized solar cells and active carbon supercapacitors

CuCo2S4 hollow spherical shell supported by RGO as an efficient counter electrode for QDSSCs: Shortening electron migration paths and promoting electron migration

In recent years, low-cost spinel sulfides as counter electrode materials for quantum dot sensitized solar cells (QDSSCs) have gradually become a research hotspot in this field. In this study, CuCo2S4/reduced graphene oxide (RGO) composite is successfully prepared via a simple and low-cost solvothermal method, which was used as counter electrode (CE) and assembled with CdS/CdSe photoanode to form QDSSCs device. In comparison with other materials, the power conversion efficiency of CuCo2S4/RGO CE reaches 6.59% and is conspicuously superior to that of pure CuCo2S4 and Cu2S/brass CE, benefiting from that the peculiar structure of the CuCo2S4 hollow spherical shell loaded on RGO nanosheets shortens electron migration paths and enables efficient transportation of electrons. Furthermore, the corrosion resistance of CEs has been prominently enhanced compared with Cu2S/brass CE. Thus, CuCo2S4/RGO composite can be primely acknowledged as promising CE materials for competitive high-performance QDSSCs and offer the possibility for high efficiency and energy saving of QDSSCs in the future.

Recent Development of Quantum Dot Deposition in Quantum Dot-Sensitized Solar Cells

Recent Development of Quantum Dot Deposition in Quantum Dot-Sensitized Solar Cells

MOF-derived CuxS double-faced-decorated carbon nanosheets as high-performance and stable counter electrodes for quantum dots solar cells

The development of highly-catalytic counter electrode (CE) materials is vital to the construction of quantum dot-sensitized solar cells (QDSCs) but is still challenging. Here, a novel self-assembly double-faced decorated carbon nanosheets with MOF-derived CuxS nanospheres (DF-CuxS/C NSs) were prepared as high-performance hybrid CEs for improving the catalytic activity towards polysulfide electrolytes and enhancing the performance of QDSCs. It is shown that the MOF-derived CuxS nanospheres disperse well on the surface of the carbon NSs in the obtained DF-CuxS/C NSs hybrids. Electrochemical characterization demonstrated that the DF-CuxS/C NSs with moderate mass ratio exhibited enhanced electrocatalytic activity towards the reduction of the polysulfide redox couple (Sn2–/S2–) and decreased charge transfer resistance at the interface of the CE/electrolyte. Benefitting from the merits of this novel hybrid CE, the power conversion efficiency (PCE) of the CdSeTe QDs-based QDSCs is increased to 9.39%, which is higher than the pristine carrageenan (CA)-derived CEs (5.84%) and Cu-BTC-derived CEs (7.74%). With the further optimization of the substrate, the highest PCE of 11.36% was achieved based on the Ti mesh substrate supported hybrid CE.

Improved efficiency of quantum dot sensitized solar cells based on TiO2/rGO/TiO2 photoanode

While quantum dot sensitized solar cells (QDSSCs) have attracted great attention, the power conversion efficiency is still far from theoretical value. To address this issue, in present work, we introduced reduced graphene oxide (rGO) into the QDSSC photoanode, and prepared TiO2/rGO/TiO2 photoanode structure. Due to the excellent conductivity of rGO, we optimized the built-in electric field in the electrode, and improved the ability for extraction, collection, and transfer of photogenerated electrons of the photoanode. Compared with cells without rGO inserting layer, the power conversion efficiency of cells based on TiO2/rGO/TiO2 photoanodes is enhanced from 2.86% to 4.03%. This work provides a way for enhancing performance of QDSSCs.

Composition, Morphology, and Interface Engineering of 3D Cauliflower‐Like Porous Carbon‐Wrapped Metal Chalcogenides as Advanced Electrocatalysts for Quantum Dot‐Sensitized Solar Cells

AbstractDesigning a low‐cost, highly efficient, and stable electrocatalyst that can synergistically speed up the reduction of polysulfide electrolytes while operative for long periods in the open air is critical for the practical application of quantum dot‐sensitized solar cells (QDSSCs), but it remains a challenging task. Herein, a simple, straightforward, and two‐step nanocomposite engineering approach that simultaneously combines metallic copper chalcogenides (MC) either Cu2−xS or Cu2−xSe with S, N dual‐doped carbon (SNC) sources for devising high‐quality counter electrode (CE) film are reported. First, the hierarchically assembled MC nanostructures are obtained using microwave‐assisted synthesis. Second, these MCs are embedded within an ordered macro–meso–microporous carbon matrix to obtain Cu2−xS@C or Cu2−xSeS@C CE. These CEs are demonstrated to have composition dependents crystal structure, surface morphologies, photovoltaic performance, and electrochemical properties. In terms of power conversion efficiency (PCE), the Cu2−xSeS@C (9.89%) and Cu2−xS@C‐CE (8.96%) constructed QDSSCs outperform both Cu2−xSe (8.96%) and Cu2−xS‐constructed (7.79%) QDSSCs, respectively. The enhanced PCE could be attributed to the synergistic interaction of S and N dopants with MC interfaces that can not only enrich electric conductivity, and a higher surface‐to‐volume ratio but also offers a 3D network for superior charge transport at the interface.

A fast combinative chemical precipitation/microwave-activated approach for the synthesis of alloyed CdSexTe1-x nanocrystals for application in quantum dot-sensitized solar cells

A fast combinative chemical precipitation/microwave-activated approach for the synthesis of alloyed CdSexTe1-x nanocrystals for application in quantum dot-sensitized solar cells

Self-switching photoelectrochromic device with low cost, plasmonic and conducting Ag nanowires decorated V2O5 and PbS quantum dots

To build an affordable photoelectrochromic energy conversion unit for self-powered smart window applications, the attractive multi-color Ag/V2O5 electrochromic counter electrode (CE) is coupled with a co-sensitized photoanode TiO2/CdS/PbS. V2O5 based devices are well-known for providing smart solutions when a voltage is applied but in this kind of configuration, the quantum dot sensitized solar cell (QDSC) drives the chromatic switching, with sunlight as the natural stimulus. The key objective in coating silver nanowires (AgNW) over the V2O5 film is to enhance the electrochromic as well as electrochemical performance of the device. AgNW impart good electrical conductivity to the layered V2O5 structure making it a promising CE and the transparency of the hybrid film in the visible-light region together with the plasmonic effect contributes to a better optical contrast. The PECD with Ag/V2O5 CE shows a transmission modulation (ΔT) of 31.1% with 45.8 cm2 C-1 coloration efficiency, which is significantly improved than with just V2O5. As compared to the liquid junction photoelectrochromic assembly, the individual films have a much higher ΔT (45.1% at 655 nm). The 5.21% power conversion efficiency (PCE) of the TiO2/CdS/PbS−S2−−Ag/V2O5 QDSC based PECD is a marked rise over that without both AgNW in the CE and PbS near infrared light harvesting QDs at the anode. This work attempts a detailed analysis of the photoelectrochromic and photovoltaic outputs of this novel PECD design with the hybrid film.

Advancing the stability and efficiency of quantum dot-sensitized solar cells through a novel, green, and water-based thixotropic biopolymer/ordered nanopores silica designed quasi-solid-state gel electrolytes

The practical application of liquid electrolyte-constructed quantum-dot sensitized solar cells (QDSSCs) is far from satisfactory due to the short-term performance, poor TiO2 penetration, leakage, and volatilization of liquid electrolytes. In this respect, three of the most critical problems with QDSSCs are addressed in this research: (i) low open-circuit voltage (VOC); (ii) low fill factor (FF), thereby, low efficiency; and, (iii) the device's poor performance stability over time. Herein, a simple approach to fabricate water-based quasi-solid-state gel electrolytes (QSSGE) designed QDSSCs by combining guar gum (GG) biopolymer and ordered nanopores silica (SBA) is reported. For the first time, SBA is being employed as an electrolyte additive to catalyze the reduction of polysulfide electrolyte more efficiently. The resultant SBA/GG gel electrolytes system offers several advantages including (i) passivating the surface trap states between TiO2/QD/electrolyte interfaces; (ii) providing a three-dimensional (3D) porous structure for the free migration of ions; (iii) its surface rich hydroxyl groups establish good contact with the photoanode. The Cu-In-S sensitized devices with SBA/GG gel electrolytes demonstrated superior power conversion efficiencies (PCE) of 9.14% in one full sunlight. This photovoltaic performance is considered to be one of the highest for copper-based QDSSCs. The outstanding PCE with gel electrolyte-constructed QDSSCs are reflected from simultaneous augmentation in VOC and FF that initiated by the synergistic interaction between SBA and GG for controlled interfacial electron-hole recombination dynamics. Moreover, gel electrolyte-constructed QDSSCs outperformed both SBA and liquid electrolyte-constructed QDSSCs in terms of performance stability, lasting up to 168 h instead of 120 or 72 h, respectively. The primary goal of this research is to develop biopolymer-based QSSGEs that are both efficient and stable while also being environmentally beneficial.

Dysprosium doping in CdTe@CdS type II core/shell and cosensitizing with CdSe for photocurrent and efficiency enhancement in quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) based on the II-VI QDs have become a promising and attractive technology due to their unique properties. However, the applications of the II-VI QDs, especially CdTe QDs, have still been restricted. Herein, a CdTe@Dy-doped CdS core/shell QDs cosensitized with CdSe QDs have been developed as a sensitizer in QDSSCs for enhancing the light-harvesting range and efficiency, accelerating charge separation, and suppressing charge recombination. The fabricated QDSSCs using TiO2/CdTe@Dy-doped-CdS/CdSe/ZnS photoanode exhibited the best short-circuit current (JSC = 20.08 mA/cm2) and power conversion efficiency (ƞ=8.26%) in comparison with that of other photoanodes comprising TiO2/CdTe, TiO2/CdTe@CdS, TiO2/CdTe@CdS/ZnS, TiO2/CdTe@CdS/CdSe/ZnS, and TiO2/CdTe@CdS/CdSe/Dy-Doped ZnS. As the obtained results from Diffuse Reflectance Spectroscopy, Photoluminescence, and Electrochemical Impedance Spectroscopy revealed, the CdTe/CdS type-II core/shell structure QDs leads to a wide absorption range, fast electron injection, and slower recombination rate because of the spatially indirect energy gap formation. Moreover, the presence of Dy cations in CdS crystal lattice boosts the charge transferring rate to the conduction band of TiO2. On the other hand, the cosensitizing of CdTe@Dy-doped CdS QDs with CdSe is advantageous not only to the electron injection and transferring but also to the hole-recovery from the valence band of QDs toward the electrolyte.

Quantum dots-sensitized solar cells: a review on strategic developments

Quantum dots-sensitized solar cells: a review on strategic developments

Microwave-assisted hydrothermal synthesis of copper selenides (Cu2−x Se) thin films for quantum dots-sensitized solar cells

In this work, copper selenide (Cu2−x Se) thin films were grown on FTO conductive glass substrates using a facile microwave-assisted hydrothermal method. The effects of synthesis parameters such as precursor components and deposition time on the stoichiometry and morphology of the synthesized films were systematically investigated through different techniques including XRD, SEM, and AFM. In order to evaluate the electrochemical catalytic performance of the synthesized copper selenide in electrolyte containing the sulfide/polysulfide redox couple, we assembled liquid-junction quantum dots-sensitized solar cells (QDSSC) using the synthesized copper selenide thin films as counter electrodes and CdSe quantum dots-sensitized mesoporous TiO2 as photoanodes. Under the illumination of one Sun (100 mW cm−2), the QDSSC assembled with the optimal copper selenide CEs (Cu:Se = 1:1) exhibited a power conversion efficiency of 2.07%, which is much higher than that of traditional Pt counter electrode (0.76%).

Graphene quantum dots and CuS microflowers anchored rGO composite counter electrode for the enhanced performance of quantum dot sensitized solar cells

Herein, a zero-dimensional graphene quantum dots (GQD) anchored on reduced graphene oxide (rGO) sheets were synthesized by hydrothermal method. CuS and GQD anchored rGO sheet (GRGS/CuS) composite was prepared by simple spin coating and thermal sulfidation techniques and used as counter electrode (CE) material for CdS quantum dot sensitized solar cell (QDSSC). The morphological studies of GRGS/CuS composite revealed the presence of spherical graphene quantum dots and microflower structured CuS on rGO sheet matrix. This microflower morphology provided more reactive sites for the electrolyte reduction and GQD/rGO in the composite acted as an effective conducting matrix to transport the charge carriers. The synergistic effect of GQD/rGO and CuS in the composite resulted in reduced charge transfer resistance and multi fold times increased the power conversion efficiency of GRGS/CuS composite than the bare counter electrodes. This work has opened up new opportunities to use GRGS/CuS composite material as a promising counter electrode, since it has the potential to enhance the performance of solar cells.

Dye Enhanced Quantum Dot Sensitized Solar Cell

Third generation solar cells, such as dye and quantum dot sensitized solar cells are attracting attention of many research groups. In this investigation we explore the role of dye extract on the enhancement of the photovoltaic properties of quantum dot sensitized solar cells (QDSSCs). Lead sulfide quantum dots of different sizes have been used to sensitize a nanostructured titanium oxide electrode. We compare the open circuit voltage, the short circuit current, and power conversion efficiency of QDSSCs with the same quantities as obtained for dye-enhanced system using pomegranate dye extract. An open circuit voltage of 166 mV, a short circuit current of 0.1 mA, and an efficiency of 0.32% were obtained for 2.4 nm radius lead sulfide quantum dot sensitized solar cells. Using pomegranate dye extract reveals a considerable enhancement of the above characteristics. The combined dye-quantum dot system produces an open circuit voltage of 300 mV, a short circuit current of 0.55 mA, and an efficiency of 3.4%. For 3.2 nm radius QDs, the efficiency is substantially higher, reaching about 7%. A model describing the structure and processes leading to the above enhancement of the assembled solar cell characteristics is presented. In this model we explain the interplay between the transfer of electrons between the dye, quantum dots, and subsequent injection in the wide band gap titanium dioxide semiconductor.

Designing novel spiro compounds as favorable hole transport materials for quantum dot sensitized photovoltaics

Some hole transport materials (HTMs) containing 9,9´-spiro-bifluorene central moiety (core) were developed to achieve high performance quantum dot sensitized solar cells (QDSSCs). The properties of all HTMs were explored via density functional theory (DFT) calculations along with Marcus and Einstein theories. It was exhibited that the HOMO and LUMO energies of all HTMs were positioned upper than the valence and conduction bands of CdS and CdSe QDs, respectively. Thus, they were appropriately aligned which could result in efficient hole injection from the CdS and CdSe QDs towards the HTMs. The negative solvation energies of all HTMs approved that they were highly stable and soluble in CH2Cl2 solution. All spiro-based HTMs displayed relatively good light harvesting efficiency (LHE) for light absorption and the materials with X = CH3 and F substituents exhibited the greatest LHE values of 0.3485 and 0.3317. Hirshfeld analysis illustrated that the H∙∙∙H contacts were the most important interactions that covered the greatest areas (41.1–71.2%) in all HTMs except for the X = CF3 which indicated F…H interaction as the most significant interaction with 42.2% surface area. The highest hole mobility (μh = 1.65 × 10-2 cm2V-1s−1) was measured for the HTM including the X = H substituent that was greater than that of the famous Spiro-OMeTAD. As a result, it was suggested as the most favorable HTM for QDSSCs as it could afford higher performances than those of Spiro-OMeTAD and other HTMs designed in this work.

Solvent-engineered performance improvement of graphene quantum dot sensitized solar cells with nitrogen functionalized GQD photosensitizers

We report for the first time that the choice of solvent used in the synthesis of nitrogen-doped graphene quantum dots (N-GQDs) has a significant effect on the photovoltaic performance of quantum dot sensitized solar cells (QDSSC) where N-GQDs work as photosensitizers. Switching from protic water (H2O) solvent to aprotic N-N dimethylformamide (DMF) causes significant change in structural, photophysical and electronic properties of N-GQDs working as active materials in QDSSC. Unlike traditional dye-sensitized solar cells, N-GQDs replace toxic and readily degradable organic dyes as an active material, due to enhanced stability, cost-efficient fabrication, and environment-friendly processing. We discussed compositional, optical, and electronic properties of N-GQDs synthesized in different solvents, and their role in the photoconversion efficiency of quantum dots sensitized solar cells. Spectroscopic results reveal that nitrogen-doped graphene quantum dots with green emission (G-GQDs) have relatively shorter effective conjugation length and lower content of pyrrolic nitrogen groups because water is a polar protic solvent, which suppresses the water elimination reaction by donating protons to the reaction medium. On the contrary, DMF, a polar aprotic solvent, cannot donate hydrogen, leading to enhanced nitrogen units in the graphene quantum dots framework and red emission (R-GQDs), thus improving carrier density and transport properties. QDSSCs fabricated from R-GQDs exhibit photovoltaic performance (PCE > 5.0%) superior to other previously reported GQD sensitized solar cells.

Composition engineered ternary copper chalcogenide alloyed counter electrodes for high-performance and stable quantum dot-sensitized solar cells

The rational design and development of economical, high-performance, and stable counter electrodes (CE) are critical to bringing the quantum dot-sensitized solar cell (QDSSCs) from the laboratory to a practical application. In this respect, we used a two-step approach to fabricate ternary copper chalcogenide (Cu 2−x S y Se 1−y ) alloyed semiconductors onto fluorine-doped tin oxide (FTO). In the first step, the binary copper chalcogenides CuS nanostructures that are synthesized using the microwave-irradiation technique are screen-printed onto the FTO substrate and annealed in a nitrogen atmosphere to obtain Cu 2−x S CE. In the second step, ternary Cu 2−x S y Se 1−y alloyed electrocatalyst is obtained through a composition engineering approach in which the elemental Se was incorporated on the surface of as-synthesized Cu 2−x S nanostructures using the drop-casting method. Compared to the pristine Cu 2−x S CE, the as-synthesized Cu 2−x S y Se 1−y CE has exhibited tunable crystal structures, compositions, morphologies. The electrochemical analysis revealed that the optimized Cu 2−x S y Se 1−y CE has exhibited low charge transfer resistance (R ct ), and excellent reduction activity to S n 2− species of the polysulfide electrolyte. Accordingly, QDSSCs assembled with Cu 2−x S y Se 1−y CE have delivered conversion efficiencies of 8.02%, which are higher than those of pristine Cu 2−x S CE (7.24%). Noticeably, Cu 2−x S y Se 1−y CE has demonstrated outstanding electrochemical stability in polysulfide redox couple , exhibiting no substantial fluctuations in either the current density or shape of the curve even after 200 continuous cyclic voltammetry (CV) cycles. Moreover, the best cell devices constructed using Cu 2−x S y Se 1−y CE validated remarkable stability under open-air conditions, retaining <60% of the original performance after 120 h of illumination. Overall, the ease of synthesis, low cost, time efficiency, and excellent electrocatalytic characteristics of the Cu 2−x S y Se 1−y alloyed semiconductors film demonstrated in this work make it an encouraging applicant for use as a CE material in photovoltaic applications. The two-step synthesis procedure of the ternary copper chalcogenide counter electrode. • Ternary copper chalcogenide (Cu 2−x S y Se 1−y ) alloyed electrocatalyst developed. • Cu 2−x S y Se 1−y exhibited compositions dependent tuneable crystal structures and surface morphologies. • Cu 2−x S y Se 1−y served as an efficient and stable counter electrode in the QDSSCs.

Highly efficient quantum-dot-sensitized solar cells with composite semiconductor of ZnO nanorod and oxide inverse opal in photoanode

Photoelectric conversion is realized by a series of processes in quantum-dot-sensitized solar cells (QDSSCs), including light capture, photoelectron generation, and electron transmission. In addition to obtaining photoelectrons, the photoanode provides a channel for electron transmission. Therefore, the photoanode plays important roles in improving the performances of QDSSCs. This paper presents the fabrication of a novel photoanode based on a semiconductor composite of ZnO nanorods and TiO2/ZnO inverse opal. QDSSCs with composite semiconductors of ZnO nanorods and oxide inverse opal in the photoanode were demonstrated to facilitate better charge transfer and reaction rates at the interface and obtain higher photocurrents and power conversion efficiencies than those of QDSSCs with pure inverse opal photoanodes. Using a CdS/CdSe co-sensitizer in the QDSSCs, a maximum cell efficiency of 8.18% was obtained, and it was further improved to 11.24% after interface modification with NH4F and ZnS.