Quantum-dot Cells Research Articles

Interface-resolved photovoltage generation dynamics and band structure evolution in a PbS quantum dot solar cell.

For directed development of solar cells using nanomaterials such as quantum dots, there is a need to understand the device function in detail. Understanding where photovoltage is generated in a device and where energy losses occur is a key aspect of this, and development of methods which can provide this information is needed. We have previously shown that time-resolved photoelectron spectroscopy of core levels can be used to follow the photovoltage dynamics at a specific interface of a lead sulfide quantum dot solar cell. Here, we use the method's selectivity and sample design to investigate the photovoltage generation in different parts of this solar cell and determine how the different layers (including the absorber layer thickness) contribute to charge separation. We show that all layers contribute to photovoltage generation and that a gold contact deposited on the quantum dots is necessary for full photovoltage generation and slow charge recombination. By combining the information obtained, we are able to experimentally follow the time evolution of the solar cell band structure during the charge separation process. Furthermore, we can identify which specific layers need to be optimized for an overall improvement of quantum dot cells. In the future, this methodology can be applied to other types of devices to provide insights into photovoltage generation mechanisms.

Hierarchical self-constructed molecular layers of small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots

Hierarchically structured self-assembled molecular layers are functionally versatile and structurally tunable, which are nanoscale molecular building blocks with a wide range of applications from biosensing systems to optoelectronic devices. Herein, we present a facile and effective strategy to fabricate hierarchical self-constructed molecular layers comprising small bifunctional molecules with strong molecular dipole moments for improvement of quantum efficiency in inorganic quantum dots (QDs) by using the cooperative interfacial self-assembly of hydrophilic bifunctional molecules on the polar electrode surface. The spontaneous construction of nanostructured molecular layers with different molecular dipole moments was simply achieved through solution-dipping and in situ interfacial self-organization of 3-mercaptopropionic acid or 1-propanethiol molecules on the surface of indium tin oxide (ITO) anode. It is experimentally revealed that these functional molecules formed uniform and ultrathin self-constructed molecular nanolayers on the ITO surface via covalent bonding, where bifunctional 3-mercaptopropionic acid molecules induced a polar molecular surface of thiol groups with strong dipole moments, whereas 1-propanethiol molecules formed a relatively hydrophobic surface of short alkyl chains with weak dipole moments. In addition, the nanoscale ultrathin nature of these molecular layers afforded high visible light transmittance comparable to that of pristine ITO substrate. The electro-optical properties of the QD cells revealed that hierarchical self-constructed molecular nanolayer with strong molecular dipole moments exhibited superior current and luminescent properties with a 162% improvement in external quantum efficiency relative to those of a conventional QD device without molecular layer. Furthermore, the self-assembled molecular nanolayer of 3-mercaptopropionic acid exhibited a higher luminescent efficiency than 1-propanethiol-based nanolayer owing to the increased hole mobility of thiol-based molecular layer with strong dipole moments.

Monolithic Two-Terminal Tandem Solar Cells Using Sb2S3 and Solution-Processed PbS Quantum Dots Achieving an Open-Circuit Potential beyond 1.1 V.

Multijunction solar cells have the prospect of a greater theoretical efficiency limit than single-junction solar cells by minimizing the transmissive and thermalization losses a single absorber material has. In solar cell applications, Sb2S3 is considered an attractive absorber due to its elemental abundance, stability, and high absorption coefficient in the visible range of the solar spectrum, yet with a band gap of 1.7 eV, it is transmissive for near-IR and IR photons. Using it as the top cell (the cell where light is first incident) in a two-terminal tandem architecture in combination with a bottom cell (the cell where light arrives second) of PbS quantum dots (QDs), which have an adjustable band gap suitable for absorbing longer wavelengths, is a promising approach to harvest the solar spectrum more effectively. In this work, these two subcells are monolithically fabricated and connected in series by a poly(3,4-ethylene-dioxythiophene) polystyrene sulfonate (PEDOT:PSS)-ZnO tunnel junction as the recombination layer. We explore the surface morphology of ZnO QD films with different spin-coating conditions, which serve as the PbS QD cell's electron transport material. Furthermore, we examine the differences in photogenerated current upon varying the PbS QD absorber layer thickness and the electrical and optical characteristics of the tandem with respect to the stand-alone reference cells. This tandem architecture demonstrates an extended spectral response into the IR with an open-circuit potential exceeding 1.1 V and a power conversion efficiency of 5.6%, which is greater than that of each single-junction cell.

Design of Multiplier Circuit Using Carry Save Adder Based on Quantum-Dot Cell Automata

The executions of various complex models reliant on quantum-dot cell automata (QCA) are of high eagerness for investigators. So far, the structure of complex adders in QCA is focused on bringing down clock delay, cell count, and logic gates. This paper proposes the circuit format of a 4-bit multiplier utilizing a carry save adder (CSA) and its implementation on QCA. The CSA is framed with another QCA design of the full adder circuit. The CSA gives preferable expansion strategies over Brent–Kung (BK) adder and Landler–Fisher (LF) adder. This multiplier represents fewer cell counts and clock delays conversely with past designs.

Combining Quantum Dot and Perovskite Photovoltaic Cells for Efficient Photon to Electricity Conversion in Energy Storage Devices

Renewable energy sources, such as wind and solar power, are increasingly important today to reduce emissions from fossil‐based energy sources. However, the electricity from wind and solar power varies over time and depends on weather conditions and the time of the day. Therefore, to include a large fraction of electricity from these energy sources in the electricity grid, large‐scale and low‐cost energy storage is needed. Herein, it is investigated how a combination of quantum dot based photovoltaic cells and perovskite‐based photovoltaic cells can be used to increase the energy conversion efficiency and increase the working range of energy storage devices based on conversion between heat, light, and electricity. The results show that these new types of photovoltaic materials have very promising properties for efficient utilization in energy storage devices, which have the potential for large‐scale and low‐cost energy storage.

Novel High-Efficiency Nanocomposite Gate Design of Quantum-Dot Cellular Automata Based on Deep Learning.

With the development of science and technology, the feature size of CMOS devices will always shrink to the limit. Therefore, some new nanodevices will eventually become substitutes for microelectronic devices. A new electronic revolution will break out. Nanoscience and technology is the high-tech frontier technology of the century and one of the main contents of scientific development in the new era. Its development will have a profound impact on other disciplines, industries, and society. Nanoelectronics is an important part of the discipline of nanoscience and technology, which represents the development trend of microelectronics and will become the foundation of the next generation of electronic science and technology. With the development of ultra-large-scale integrated circuits, the feature size of electronic devices is getting smaller and smaller and has entered the nanoscale from the microscale. When the size of the system is small enough to be compared with the wavelength of electrons, the quantum effect becomes the dominant current-carrying main factor in child behavior. While these new phenomena and new effects bring challenges to the original semiconductor devices, they also provide opportunities for the development of new devices. Evolutionary circuit design is based on cellular neural network and quantum-dot cells, designs combinational logic circuits through the evolutionary algorithm, uses the logic gate based on cellular neural network design as the population gene of evolutionary circuit design, enriches the diversity of the population, and improves the evolutionary algorithm at the same time, the success rate of the improved genetic algorithm for evolutionary circuits has been greatly improved, and the failure rate has been reduced from 14% to 2%, obtaining a faster evolution speed and improving the performance of the evolution circuit.

An energy efficient high-speed quantum-dot based full adder design and parity gate for nano application

Quantum-dot cellular automata (QCA) are novel prominent emerging nano-computational nanoelectronics technology at the nanoscale. It facilitated computation paradigms and promises an alternative good solution to traditional transistor CMOS technology with faster speed, very low energy dissipation, higher scale integration, small size, low latency/delay of circuits, and higher switching frequency. It is one of the most valuable nanotechnologies (or Nanotech) that effort to fabricate general computational at the nanoscopic-scale by commanding the position of electrons. In this paper, we have proposed the design of novel robust full adder, testable even and odd parity circuits using coplanar single layer in quantum-dots cellular automata nanotechnology. The proposed design of full adder circuits used only 36 quantum dots cells, occupied a design area of 0.04 µm2, and minimum delay count is 0.75 clock cycles. The proposed circuit’s investigated by novel QCADesigner-E (Energy) tool on using coherence vector (w/Energy) engine and optimized the energy-dissipation (ED) of full adder circuit. In the proposed design do not use coplanar multilayer and 45-degree rotated cells but used regular synchronized clock cycle and minimum quantum-dots cells. Therefore overall manufacturability of the robust full adder circuits significantly more improves as compared to the existing design. The presented robust full adder design have been calculated the total ED (Sum_Ebath) is 1.70e−002 eV (Error: +/- −1.63e−003 eV), and average ED/cycle (Avg_Ebath) is 1.54e−003 eV (Error: +/- −1.48e−004 eV).

New Design of Binary to Ternary Converter

Ternary quantum-dot cell automata (TQCA) are a relatively new quantum structure in QCA. The design of ternary digital circuits with this type of structure is increasing because of its proximity to fuzzy logic. The use of multi value logic (MVL) increases circuit density and gives more information about the variable. Designing a circuit combined of binary QCA (bQCA) and TQCA requires interaction between these two technologies, and to create this interaction a converter is used to convert binary to ternary, which is a useful interface. In fact, binary to ternary design can be used as a link between QCA technology at various levels and new multi-value QCA cell structures can be used. In this paper, a new binary-to-ternary converter is introduced. The proposed circuit simulation is presented to show the correct performance of the proposed converter by MATLAB software.

Quantum dot solar cell: an emerging nanomaterial-based device in the solar industry

The worldwide energy is on the cusp of monstrous alter, driven by an unquenchable request and an increasing mindfulness of the constrained supply and corrupting environment of fossil fuels. More intensive research has been conducted around the world to get different economical energy arrangements. Quantum dot manufactured sun powered cell is the innovation for long run, which can give required efficiency to run the solar industry facing with various challenges underneath silicon photovoltaic cell. Quantum dot cells are most flexible frame of renewable vitality since of its unique properties for producing power, warming as well as desalinating water. QD's have bandgaps which are flexible over a wide range of energy levels by changing the dot size. Semiconductor QDs, due to their quantum-based properties, give a modern pathway for controlling energy stream. In this manner, they have the tremendous potential to elevate the efficiency of solar photovoltaic cells. Herein, we have collectively summarised the advancements of quantum dot solar cell. We are foreseeing that this review will certainly help the researchers for more serious examination of investigations of the nanomaterial in various innovative ranges.

Direct visualization of the photovoltaic effect in a single-junction GaAs cell via in situ electron holography

The nanoscale electric potential distribution in a gallium arsenide single p–n junction cell under artificial illumination, or the photovoltaic (PV) effect, was investigated using in situ electron holography with a transmission electron microscope. A custom-made specimen holder with biasing and illumination capabilities was used for this purpose. To determine the practical potential of the specimen prepared by a focused ion beam (FIB), the thickness of active layers that directly contribute to the PV effect was accurately derived by analyzing the results of in situ biasing electron holography. In situ light-illumination electron holography directly visualized the PV effect in the cell, where the potential difference between the p and n regions decreased with the increase in the intensity of light illumination. Using PV simulations, in conjunction with some reasonable assumptions regarding the practical specimen parameters in the FIB-milled specimen, we can generate a credible explanation of the experimental result. These findings will help to fully understand the PV effect in various types of solar cells, including perovskite and quantum dot cells.

Triangular Quantum-Dot Cellular Automata Wire for Standard Ternary Logic

Quantum-dot cellular automata (QCA) is a computational paradigm that is based on encoding information in terms of the configuration of charge among quantum dots without requiring current switches. Mostly, QCA cells have been realized by employing the electron switching in square quantum-dot cells. In this paper, a triangular metal-dot cell with a single electron is proposed to represent ternary information. Then, an inverter chain of the proposed triangle cells is suggested through juxtaposing the cells. Additionally, wire crossing and wire fan-out are the two inseparable subjects of QCA wire. A wire-crossing method is presented for the proposed ternary wire. Wire fan-out is also dealt with in this paper by an innovative approach. The correctness of operation of proposed cells and wires are thoroughly verified by applying the physical relations.

Utilizing charge reconfigurations of quantum-dot cells in building blocks to design nanoelectronic adder circuits

In the quantum-dot cellular automata (QCA) nanotechnology, the cell-based building block can be designed by utilizing the charge reconfiguration of quantum-dot cells in order to achieve the desired function with optimal implementation. In this paper, new advanced nanostructures based on quantum-dot cells are introduced to three-input XOR gate and two-to-one multiplexer, which can be considered in addition to the conventional majority voter as basic building blocks used in implementing well-optimized QCA circuits. Consequently, these blocks are used in this paper to implement new single-layer QCA full-adders and four-bit adders as motivational applications. Moreover, an innovative design approach of full-adder is proposed to avoid the presence of inputs surrounded by QCA cells and to prevent the use of crossovers when building multi-bit adders. The proposed QCA layouts are simulated and evaluated as results indicate that proposed designs are superior to the previous designs in the literature.

Efficiency Improvement Analysis for Recent High-Efficient Solar Cells

The entire electricity demand of the whole earth, can be theoretically satisfied by harnessing the unlimited photon energy of the alpha source, the sun. Absorbing the solar power in a full efficient way is still on progress, due to the limitation of our solar cell technology. On commercial aspects, it is also promising but not up to the mark. Recent high efficient solar cell still leaves more space to improve the cell efficiency. On these circumstances, the use of Graphene, Multi-Junction Cells and Quantum Dot Cells will be helpful to increase the rate of recent research flow. This paper visualizes GaAs, InP, CdTe and Graphene implementations on four proposed basic models, which have showed a positive impact to overcome the losses and SQ limits. These models also postulate the maximization of the solar cell efficiency, omitting the corresponding losses along with maintaining the inter-junction relation suitably.

Application of MEG in Increasing External Quantum Efficiency Over 100%

This review paper focuses on increasing the efficiency of Solar cell using Quantum Dot. The principle idea is using MEG (Multiple exciton Generation). MEG is more efficient in quantum confined nanostructures than in bulk semiconductors because the momentum preservation prerequisite is relaxed. Even the carrier-carrier interactions are huge due to strong confinement. The carrier multiplication decoupling from the effective band gap allows amplified photo-voltage for corresponding carrier multiplication. Along with this, it was also found that external quantum efficiency (EQE) would reach almost 100%, sometimes even exceeding it, for energy which is greater than twice the band gap energy. This is due to the fact that high energy photons have the ability to produce more than one photo carrier pair. MEG is definitely a promising route to increasing solar cell efficiency. If a threshold of twice the band gap energy could be realized for impact ionization in a colloid Quantum Dot cell, the theoretical maximum possible conversion efficiency would shift to above 60%. The goal is to capture maximum energy incident on a given plane and targeting highyield transportation of the resultant photo generated charge.

Design and Implementation of Content Addressable Memory Unit using Qunatum Dot

Quantum-dot cell automata is one of the upcoming new advances at the nanoscale that can be a reasonable substitution for CMOS innovation. The circuits built in QCA technology have attractive features like low power utilization, and low size. These features can be progressively particular in memory structures. In this paper, the new design another structure for substance addressable memory cell in QCA. For this reason, initial, an extraordinary gate is presented for mask task in QCA and afterward this gate is utilized to enhance the execution of CAM. These structures are assessed with QCA Designer test system.

Review of Power Device for Solar-Powered Aircraft Applications

This paper reviews various power device components of solar-powered aircraft such as photovoltaic (PV) cells, maximum power point tracker (MPPT) and rechargeable batteries. The various power device components were highlighted, and the ones applicable to aircraft were analyzed, based on criteria as efficiency for photovoltaic cells; energy densities about rechargeable batteries; and maximum power point tracker on quick response to achieve maximum power point on I-V curve. Emerging technologies like photovoltaic cells, thin film cell, organic photovoltaic cell, multi-junction cell and silicon quantum dot cell, with the future potential of high efficiencies that can be used in solar-powered aircraft, were all examined. Regarding battery technology, Lithium-air battery (Li-air) was reported as having great opportunities for high energy densities capable of improving the efficiency of the solar-powered aircraft, for the greater prospect of the aviation industry. The design of efficient power device for solar-powered aircraft application is proposed. Gallium Arsenide (GaAs) solar cells were used because of its high energy conversion efficiency of 30 to 40%. A smart and intelligent MPPT Artificial Neural Network (ANN) is chosen because of its efficiency in partial shading and fast response and speed. The Li-air rechargeable battery is proposed because of its theoretical energy density of 11680 Wh/Kg.

Adder with Efficient Speed and Area by Using Quantum-Dot Cellular Automata Technology

The lessening in transistor estimate by following field’s law made chip unpredictability with more computational capacity. The present size of the transistor needs to decrease more, which prompts nanotechnology. The quantum-dot cell automata come extremely close to nanotechnology presents one of the conceivable arrangements in defeat this physical breaking point, even though the designs with QCA technology are not a fundamental basic. In this brief by considering quantum-dot cell automata (QCA) innovation idea a greater part door based adder is outlined. The effectiveness in territory and speed by larger part entryway idea based adders are executed and contrasted with beforehand technique plans by utilizing verilog coding mimicked in Xilinx. The proposed one-piece QCA viper depends on another calculation that requires just three larger part entryways and two inverters for the QCA expansion. Novel 128-bit adders designed in QCA become accomplished.

(Invited) Metal Halide Perovskites at the Nanoscale: High Quality Optoelectronic Materials with Unique Phase Properties

The newly rediscovered perovskite semiconductor system has the potential to be extremely transformative for all optoelectronic devices, especially photovoltaics (PVs). Perovskite semiconductors of the form APbI3 where A is a large +1 charged cation, typically Cs, methylammonium, or formamidinium have had a huge resurgence among materials scientists for outstanding PV properties despite being overlooked for decades. Semiconductors containing the latter two A-site cations listed are hybrid organic-inorganic materials, and as such, are far less understood compared to conventional all inorganic or even organic material systems. Regardless of this spotty formal understanding, lead-halide perovskites have very rapidly been optimized to power conversion efficiency levels on par with all other materials even with extensive history of research. Perovskites show a unique tolerance to crystalline defects that cause trouble in most other semiconductors. Therefore the potential offered is that very high efficiency PVs can be fabricated in extremely fast and inexpensive ways, thus offering a revolution for the solar industry and a direct route toward producing the world’s energy with a simple and clean technology. Long-term durability of the devices is the critical remaining challenge to be solved.1 Two examples of major instabilities in device performance are the volatility of the organic cation and the specific crystal habit in which the material embodies. Nanoscale versions (often termed quantum dots (QDs)) of the all-inorganic metal halide perovskite (CsPbI3) tend to retain the desired perovskite phase due to strain effects at the surface of the QDs whereas conventional films of the same material “relax” to an orthorhombic non-perovskite structure at room temperature. Therefore these QDs potentially solve both of the instability issues. The cubic CsPbI3 QD cells operate with a rather remarkable open-circuit voltage of >1.2 volts and have produced power conversion efficiencies over 13%.2,3 This customizable new nanomaterial system has incredible potential for many applications in optoelectronics, including photovoltaics, LEDs, displays and lasers. We describe the formation of perovskite phase-CsPbI3 QD films with long range electronic transport that retain the high temperature phase in ambient conditions making up the active layer in optoelectronic devices. Perspectives on how this technology can become transformative will be discussed. References A. Christians, P. Schulz, J.S. Tinkham, T.H. Schloemer, S.P. Harvey, B.J .Tremolet de Villers, A. Sellinger, J.J. Berry, J.M. Luther, Nature Energy, 2018, 3 (1), 68.Swarnkar, A.R. Marshall, E.M. Sanehira, B.D. Chernomordik, D.T. Moore, J.A. Christians, T. Chakrabarti, J.M. Luther, Science, 2016, 354 (6308), 92-95.M. Sanehira, A.R. Marshall, J.A. Christians, S.P. Harvey, P.N. Ciesielski, L.M. Wheeler, P. Schulz, L.Y. Lin, M.C. Beard, J.M. Luther, Science Advances, 2017, 3 (10), eaao4204.

Enhancing Loading Amount and Performance of Quantum-Dot-Sensitized Solar Cells Based on Direct Adsorption of Quantum Dots from Bicomponent Solvents.

Intrinsically weak interaction between oil-soluble quantum dots (QDs) and TiO2 in a direct adsorption process limits QD loading and the performance of QD-sensitized solar cells (QDSCs). Herein, the underlying chemistry and mechanisms governing QD adsorption on TiO2 were studied to improve QD loading and cell performance. Experimental results indicate that solvent polarity plays the crucial role in determining QD loading. Compared with single-component solvents, substantially greater QD loading can be realized at the critical point (CP) of bicomponent solvents, where QDs become metastable and start to precipitate. Through this strategy, average efficiency of 12.24% was obtained for ZCISe QDSCs, which is comparable to those based on the capping ligand induced self-assembly route. This report demonstrates the great potential of bicomponent solvents at the CP for high QD loading and excellent cell performance and presents a platform for assembling functional composites with the use of different nanocrystals and substrates.

High performance solid state solar cells incorporating CdS quantum dots and CH3NH3PbI3 perovskite

Abstract Since 2012, halide perovskites CH3NH3PbX3 (X = Cl, Br, or I) have been the topic of intensive research due to their excellent structural, optical and electronic properties and their application to perovskite solar cells (PSCs). PSCs are a new type of third-generation photovoltaics presenting low cost, ease of construction and power conversion efficiencies (PCEs) exceeding 23%, challenging the Si-based devices. This work describes a novel solution processed PSC structure: FTO/TiO2(CL)/mp-TiO2/CdS/Perovskite/Spiro-MeOTAD/Ag, using co-sensitization of quantum dots (QDs) with perovskite materials. This new cell architecture improves the device performance and characteristics and gives us the opportunity to develop solid state QDs cells.