Enhancing quantum dot solar cell efficiency to 11.53%



enhancingquaFigure 1. Shown above is the structure of CQDSC and the optical redistribution profiles of devices by TMF optical simulation. Credit: Professor Sung-Yeon Jang, UNIST

A novel technology that can improve the efficiency of quantum dot solar cells to 11.53% has been unveiled. Published in the February 2020 issue of Advanced Energy Materials, it has been evaluated as a study that solved the challenges posed by the generation of electric currents from sunlight by solar cells by enhancing the hole extraction.

A research team, led by Professor Sung-Yeon Jang in the School of Energy and Chemical Engineering at UNIST has developed a  that maximizes the performance of quantum dot solar  by using .

Solar cells use a characteristic of which electrons and holes are generated in the absorber layer. The free free electrons and hole then move through the cell, creating and filling in holes. It is this movement of electrons and holes that generate electricity. Therefore, creating multiple  and transporting them are an important consideration in the design of efficient solar cells.

The research team switched one side of the quantum dot solar cells to organic hole transport materials (HTMs) to better extract and transport holes. This is because the newly-developed organic polymer not only possesses superior hole extracting ability, but also prevents electrons and holes from recombining, which allow efficient transport of holes to the anode.

Generally, quantum dot solar cells combine electron-rich quantum dots (n-type CQDs) and hole-rich quantum dots (p-type QDs). In this work, the research team developed organic π‐conjugated polymer (π‐CP) based HTMs, which can achieve performance superior to that of state‐of‐the‐art HTM, p‐type CQDs. The molecular engineering of the π‐CPs alters their optoelectronic properties, and the charge generation and collection in colloidal quantum dot solar cells (CQDSCs), using them are substantially improved.

As a result, the research team succeeded in achieving power conversion efficiency (PCE) of 11.53% with decent air‐storage stability. This is the highest reported PCE among CQDSCs using organic HTMs, and even higher than the reported best solid‐state ligand exchange‐free CQDSC using pCQD‐HTM. “From the viewpoint of device processing, device fabrication does not require any solid‐state ligand exchange step or layer‐by‐layer deposition process, which is favorable for exploiting commercial processing techniques,” noted the research team.

“This study solves the problem of hole transport, which has been the major obstacle for the genration of electric currents in quantum dot ,” says Professor Jang. “This work suggests that the molecular engineering of organic π‐CPs is an efficient strategy for simultaneous improvement in PCE and processability of CQDSCs, and additional optimization might further improve their performance.”


Explore further

Light on efficiency loss in organic solar cells


More information: Muhibullah Al Mubarok et al. Molecular Engineering in Hole Transport π‐Conjugated Polymers to Enable High Efficiency Colloidal Quantum Dot Solar Cells, Advanced Energy Materials (2020). DOI: 10.1002/aenm.201902933

Journal information: Advanced Energy Materials

Breakthrough Quantum-Dot Transistors Open the Door to a Host of Innovative Electronics


By depositing gold (Au) and Indium (In) contacts, researchers create two crucial types of quantum dot transistors on the same substrate, opening the door to a host of innovative electronics. Credit: Los Alamos National Laboratory/University of California, Irvine

Quantum dot logic circuits provide the long-sought building blocks for innovative devices, including printable electronics, flexible displays, and medical diagnostics.

Researchers at Los Alamos National Laboratory and their collaborators from the University of California, Irvine have created fundamental electronic building blocks out of tiny structures known as quantum dots and used them to assemble functional logic circuits. The innovation promises a cheaper and manufacturing-friendly approach to complex electronic devices that can be fabricated in a chemistry laboratory via simple, solution-based techniques, and offer long-sought components for a host of innovative devices.

“Potential applications of the new approach to electronic devices based on non-toxic quantum dots include printable circuits, flexible displays, lab-on-a-chip diagnostics, wearable devices, medical testing, smart implants, and biometrics,” said Victor Klimov, a physicist specializing in semiconductor nanocrystals at Los Alamos and lead author on a paper announcing the new results in the October 19, 2020, issue of Nature Communications.

For decades, microelectronics has relied on extra-high purity silicon processed in a specially created clean-room environment. Recently, silicon-based microelectronics has been challenged by several alternative technologies that allow for fabricating complex electronic circuits outside a clean room, via inexpensive, readily accessible chemical techniques. Colloidal semiconductor nanoparticles made with chemistry methods in much less stringent environments are one such emerging technology. Due to their small size and unique properties directly controlled by quantum mechanics, these particles are dubbed quantum dots. 

A colloidal quantum dot consists of a semiconductor core covered with organic molecules. As a result of this hybrid nature, they combine the advantages of well-understood traditional semiconductors with the chemical versatility of molecular systems. These properties are attractive for realizing new types of flexible electronic circuits that could be printed onto virtually any surface including plastic, paper, and even human skin. This capability could benefit numerous areas including consumer electronics, security, digital signage, and medical diagnostics.  

A key element of electronic circuitry is a transistor that acts as a switch of electrical current activated by applied voltage. Usually transistors come in pairs of n- and p-type devices that control flows of negative and positive electrical charges, respectively. Such pairs of complementary transistors are the cornerstone of the modern CMOS (complementary metal oxide semiconductor) technology, which enables microprocessors, memory chips, image sensors, and other electronic devices.

The first quantum dot transistors were demonstrated almost two decades ago. However, integrating complementary n- and p-type devices within the same quantum dot layer remained a long-standing challenge. In addition, most of the efforts in this area have focused on nanocrystals based on lead and cadmium. These elements are highly toxic heavy metals, which greatly limits practical utility of the demonstrated devices.

The team of Los Alamos researchers and their collaborators from the University of California, Irvine have demonstrated that by using copper indium selenide (CuInSe2) quantum dots devoid of heavy metals they were able to address both the problem of toxicity and simultaneously achieve straightforward integration of n- and p-transistors in the same quantum dot layer. As a proof of practical utility of the developed approach, they created functional circuits that performed logical operations.

The innovation that Klimov and colleagues are presenting in their new paper allows them to define p- and n-type transistors by applying two different types of metal contacts (gold and indium, respectively). They completed the devices by depositing a common quantum dot layer on top of the pre-patterned contacts. “This approach permits straightforward integration of an arbitrary number of complementary p- and n-type transistors into the same quantum dot layer prepared as a continuous, un-patterned film via standard spin-coating,” said Klimov.

Reference: “Solution-processable integrated CMOS circuits based on colloidal CuInSe2 quantum dots” by Hyeong Jin Yun, Jaehoon Lim, Jeongkyun Roh, Darren Chi Jin Neo, Matt Law and  Victor I. Klimov, 19 October 2020, Nature Communications.
DOI: 10.1038/s41467-020-18932-5

Funding: This work was supported by the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory under project 20200213DR and the University of California (UC) Office of the President under the UC Laboratory Fees Research Program Collaborative Research and Training Award LFR-17-477148.

Scientists create solar panel by combining protein and quantum dots


2-sunCredit: CC0 Public Domain

Scientists at the National Research Nuclear University MEPhI (Russia) have created a new type of solar panel based on hybrid material consisting of quantum dots (QDs) and photosensitive protein. The creators believe that it has great potential for solar energy and optical computing.

The results of the MEPhI study were published in Biosensors and Bioelectronics.

Archaeal proteins of unicellular organisms, , can convert the energy of light into the energy of chemical bonds (like chlorophyll in plants). This occurs due to the transfer of a positive charge through the . Bacteriorhodopsin acts as a , which makes it a ready-to-use natural element of the solar panel.

A key difference between bacteriorhodopsin and chlorophyll is its ability to operate without oxygen, allowing the archaea to live in very aggressive environments like the depths of the Dead Sea. This ability has evolutionarily led to their high chemical, thermal, and optical stability. At the same time, by pumping protons, bacteriorhodopsin changes color many times in a billionth of a second. This is why it is a promising material for creating holographic processing units.

Scientists of MEPhI have been able to significantly improve the properties of bacteriorhodopsin by binding it to quantum dots (QDs)—semiconductor nanoparticles capable of concentrating  on a scale of just a few nanometers and transmitting it to bacteriorhodopsin without emitting light.

“We have created a highly efficient, operating photosensitive cell that generates electrical current by converting light under very low photon excitation. Under normal conditions, such a cell doesn’t work because photosensitive molecules such as bacteriorhodopsin effectively absorb light only in a very narrow energy range. But quantum dots do this in a very wide range and can even convert two lower-energy photons into one high-energy photon as if stacking them,” a researcher at MEPhI and one of the authors of the study, Viktor Krivenkov said.

According to the researcher, creating conditions for the radiation of high-energy photon, a quantum dot may not radiate it but rather transmit it to bacteriorhodopsin. Thus, MEPhI scientists have engineered a cell capable of operating under the irradiation from the near-infrared to the ultraviolet regions of the optical spectrum.

“We use an interdisciplinary approach at the intersection of chemistry, biology, particle physics and photonics. Quantum dots are produced using chemical synthesis methods, then they are coated with molecules that make their surface simultaneously biocompatible and charged, after which they are bound to the surface of the archean bacteriorhodopsin -containing purple membranes of Halobacterium salinarum. As a result, we have obtained hybrid complexes with very high (about 80%) efficiency of excitation  transfer from  to bacteriorhodopsin,” the leading scientist of the MEPhI Nano-Bioengineering Laboratory, Igor Nabiev said.

According to the researchers, the obtained results show the potential for creating highly effective photosensitive elements based on biostructures. They may be used, not only to provide , but also in optical computing.

The authors emphasized the very high quality of the bio-hybrid nanostructured material and the prospect of surpassing the best commercial samples with a possible increase in efficiency by a substantial margin. The next goal of the research team in this direction is to optimize the structure of the photosensitive cell.


Explore further

Protein changes precede photoisomerization of retinal chromophore


More information: Victor Krivenkov et al. Remarkably enhanced photoelectrical efficiency of bacteriorhodopsin in quantum dot – Purple membrane complexes under two-photon excitation, Biosensors and Bioelectronics (2019). DOI: 10.1016/j.bios.2019.05.009

Journal information: Biosensors and Bioelectronics

Combining Blockchain and Nanotechnology to Fight Criminal Counterfeiters and Build Brand Trust


Dotz Nano 2 images

Say the word “blockchain” to businesspeople and you’re likely to be met with either a “never heard of it” or an “it’s also called bitcoin isn’t it?” response. These kinds of comments are probably well known to those involved in nanotechnology. The reality is that neither of these transformational technologies are yet widely understood, and real-world applications are only now emerging to address business opportunities.

While blockchain is perhaps best known as the technology that underpins the (somewhat notorious) cryptocurrency called bitcoin, it can be applied to many different business areas like finance, healthcare, identity and supply chain. Major IT companies, such as IBM, Microsoft, SAP and Oracle, have invested big in making blockchain usable by business enterprises for these applications, and more.

In this article, we’ll highlight how the combination of blockchain and nanotechnology can be applied to a particularly challenging aspect of supply chain management, namely the huge global criminal marketplace in counterfeit goods, which hurts business profits, impacts brand trust and undermines customer relationships.

First, a quick primer on blockchain. A blockchain is a type of database that is tamper proof. Data stored in a blockchain cannot be changed (the technical term is immutable), it can be shared among multiple users, and significantly the composition of the data stored is agreed to by multiple users of the blockchain before it can be stored (this process is known as consensus). In short, blockchains are an incredibly secure way to keep information safe and consistent among multiple participants in a business network.

blockchain-share 2READ MORE: How Blockchain Technology Could Be The Primary Key To Cybersecurity

Next, a few words about the shadowy world of counterfeit goods. Sadly, it’s a big business for criminals. Recent industry statistics suggest counterfeiting is a $1.8 Trillion endeavor that spans the globe. Just about every product is a target for counterfeiters – luxury fashion accessories, wine, auto parts, pharmaceuticals, sports apparel and consumer electronics are common examples – and this activity impacts businesses and their brands both financially and reputationally and can represent a significant safety risk for consumers.

So how is the combination of blockchain and nanotechnology being leveraged to fight the counterfeiters?

At Quantum Materials Corp. we have developed nanomaterials called quantum dots over the past decade. Quantum dots are nanoscale semiconductor particles that possess notable and extremely useful optical and electrical properties. They measure from 10 to 100 atoms in size (approximately 10,000 dots would fit across the diameter of a human hair) and they generate light when energy is applied to them or generate energy when light is applied.

QMC creates in commercial quantities quantum dots that can be finely tuned to emit predetermined wavelengths of light (in both the visible and non-visible spectrums) with the ability to create billions of unique optical signatures. Moreover, they are excitable by numerous excitation energy sources.

Our quantum dots can be incorporated into almost any physical item at time of manufacture, and then provide a unique light signature that establishes absolute product identity. These identities are impossible to copy or clone so that products enhanced by them can be verified as being genuine items and not counterfeits.

Dotz Nano 1 qLGnFZZt

 

Read About Another New Quantum Dot Security Company Dotz Nano ~ Tag – Trace – Verify

Dotz is a technology leader, specializing in the development and marketing of novel advanced carbon-based materials used for tracing, anti-counterfeiting and product-liability solutions. Our unique products: ValiDotz ™, Fluorensic™, and BioDotz™ can be imbedded into plastics, fuels, lubricants, chemicals, and even Cannabis  plants to create product specific codes and trace for origin Twitter Icon 042616.jpg Follow Dotz Nano on Twitter

When the quantum dot signature of a product is scanned (via a hand-held scanner or an app on a smartphone), a digital representation is created that is stored on our secure and tamper-proof blockchain platform. It is this platform that allows for tracking of products providing visibility among all participants in their supply chain – from manufacture to customer purchase.

In addition, the blockchain platform is also used to store the unique digital identities of individual customers, and to tie ownership of a product to a customer at purchase time. No longer is it necessary to keep the receipt!

For example, a customer purchasing a luxury handbag that has QMC’s quantum dots incorporated into it by its manufacturer can use their smartphone to scan the bag to give them confidence that the bag is genuine. As a bonus, the manufacturer is notified that the bag’s authenticity has been checked and can offer a warranty or loyalty program to the customer in order to establish an enduring brand/customer relationship.

The bottom line for blockchain plus nanotechnology is that … it certainly impacts the bottom line. Surveys conducted by retailers point to customers not only appreciating being able to prove product authenticity but tending to buy more products where that functionality is available. They also frequent the retailer more often. Almost everyone is a winner – the customer, the retailer and the product brand. The criminal counterfeiters? Not so much.

By Stephen Squires, Founder & CEO, Quantum Materials Corp

High-Performance ‘Quantum Dot Mode-Locked Laser on silicon – Proven 4.1 Terabit-per-second transmission capacity – The Future of Telecommunications and Data Centers – UC Santa Barbara


Bowers Liu Optica

Ten years into the future.

That’s about how far UC Santa Barbara electrical and computer engineering professor John Bowers and his research team are reaching with the recent development of their mode-locked quantum dot lasers on silicon.

It’s technology that not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.

“The level of data traffic in the world is going up very, very fast,” said Bowers, co-author of a paper on the new technology in the journal Optica. Generally speaking, he explained, the transmission and data capacity of state-of-the-art telecommunications infrastructure must double roughly every two years to sustain high levels of performance. That means that even now, technology companies such as Intel and Cisco have to set their sights on the hardware of 2024 and beyond to stay competitive. quantum-dots-head-672x371

Enter the Bowers Group’s high-channel-count, 20 gigahertz, passively mode-locked quantum dot laser, directly grown — for the first time, to the group’s knowledge — on a silicon substrate. With a proven 4.1 terabit-per-second transmission capacity, it leaps an estimated full decade ahead from today’s best commercial standard for data transmission, which is currently reaching for 400 gigabits per second on Ethernet.

The technology is the latest high-performance candidate in an established technique called wavelength-division-multiplexing (WDM), which transmits numerous parallel signals over a single optical fiber using different wavelengths (colors). It has made possible the streaming and rapid data transfer we have come to rely on for our communications, entertainment and commerce.

The Bowers Group’s new technology takes advantage of several advances in telecommunications, photonics and materials with its quantum dot laser — a tiny, micron-sized light source — that can emit a broad range of light wavelengths over which data can be transmitted.

“We want more coherent wavelengths generated in one cheap light source,” said Songtao Liu, a postdoctoral researcher in the Bowers Group and lead author of the paper. “Quantum dots can offer you wide gain spectrum, and that’s why we can achieve a lot of channels.” Their quantum dot laser produces 64 channels, spaced at 20 GHz, and can be utilized as a transmitter to boost the system capacity.

The laser is passively ‘mode-locked’ — a technique that generates coherent optical ‘combs’ with fixed-channel spacing — to prevent noise from wavelength competition in the laser cavity and stabilize data transmission.

This technology represents a significant advance in the field of silicon electronic and photonic integrated circuits, in which the primary goal is to create components that use light (photons) and waveguides — unparalleled for data capacity and transmission speed as well as energy efficiency — alongside and even instead of electrons and wires. Silicon is a good material for the quality of light it can guide and preserve, and for the ease and low cost of its large-scale manufacture. However, it’s not so good for generating light.

“If you want to generate light efficiently, you want a direct band-gap semiconductor,” said Liu, referring to the ideal electronic structural property for light-emitting solids. “Silicon is an indirect band-gap semiconductor.” The Bowers Group’s quantum dot laser, grown on silicon molecule-by-molecule at UC Santa Barbara’s nanofabrication facilities, is a structure that takes advantage of the electronic properties of several semiconductor materials for performance and function (including their direct band-gaps), in addition to silicon’s own well-known optical and manufacturing benefits.

This quantum dot laser, and components like it, are expected to become the norm in telecommunications and data processing, as technology companies seek ways to improve their data capacity and transmission speeds.

“Data centers are now buying large amounts of silicon photonic transceivers,” Bowers pointed out. “And it went from nothing two years ago.”

Since Bowers a decade ago demonstrated the world’s first hybrid silicon laser (an effort in conjunction with Intel), the silicon photonics world has continued to create higher efficiency, higher performance technology while maintaining as small a footprint as possible, with an eye on mass production. The quantum dot laser on silicon, Bowers and Liu say, is state-of-the-art technology that delivers the superior performance that will be sought for future devices.

“We’re shooting far out there,” said Bowers, who holds the Fred Kavli Chair in Nanotechnology, “which is what university research should be doing.”

Research on this project was also conducted by Xinru Wu, Daehwan Jung, Justin Norman, MJ Kennedy, Hon K. Tsang and Arthur C. Gossard at UC Santa Barbara.

Story Source:

Materials provided by University of California – Santa BarbaraNote: Content may be edited for style and length.

Los Alamos National Laboratory – Stable light from ‘squashed’ Quantum Dots provide viable alternative to presently employed nanoscale light sources used in the Commercialization of quantum-dot displays, TV’s and more …


quantumdotsl
Novel colloidal quantum dots are formed of an emitting cadmium/selenium (Cd/Se) core enclosed into a compositionally graded CdxZn1-xSe shell wherein the fraction of zinc versus cadmium increases towards the dot’s periphery. Due to a …more

 

” The new colloidal processing techniques allow for preparation of virtually ideal quantum-dot emitters with nearly 100 percent emission quantum yields shown for a wide range of visible, infrared and ultraviolet wavelengths. These advances have been exploited in a variety of light-emission technologies, resulting in successful commercialization of quantum-dot displays and TV sets … “

Intentionally “squashing” colloidal quantum dots during chemical synthesis creates dots capable of stable, “blink-free” light emission that is fully comparable with the light produced by dots made with more complex processes. The squashed dots emit spectrally narrow light with a highly stable intensity and a non-fluctuating emission energy. New research at Los Alamos National Laboratory suggests that the strained colloidal quantum dots represent a viable alternative to presently employed nanoscale light sources, and they deserve exploration as single-particle, nanoscale light sources for optical “quantum” circuits, ultrasensitive sensors, and medical diagnostics.

squashed quantum dot morestableli

“In addition to exhibiting greatly improved performance over traditional produced , these new strained dots could offer unprecedented flexibility in manipulating their emission color, in combination with the unusually narrow, ‘subthermal’ linewidth,” said Victor Klimov, lead Los Alamos researcher on the project. “The squashed dots also show compatibility with virtually any substrate or embedding medium as well as various chemical and biological environments.”

The new colloidal processing techniques allow for preparation of virtually ideal quantum-dot emitters with nearly 100 percent emission quantum yields shown for a wide range of visible, infrared and ultraviolet wavelengths. These advances have been exploited in a variety of light-emission technologies, resulting in successful commercialization of quantum-dot displays and TV sets.

The next frontier is exploration of  as single-particle, nanoscale light sources. Such future “single-dot” technologies would require particles with highly stable, nonfluctuating spectral characteristics. Recently, there has been considerable progress in eliminating random variations in emission intensity by protecting a small emitting core with an especially thick outer layer. However, these thick-shell structures still exhibit strong fluctuations in emission spectra.

los alamos xlosalamoslogo.png.pagespeed.ic.w4zn0ixzm6In a new publication in the journal Nature Materials, Los Alamos researchers demonstrated that spectral fluctuations in single-dot emission can be nearly completely suppressed by applying a new method of “strain engineering.” The key in this approach is to combine in a core/shell motif two semiconductors with directionally asymmetric lattice mismatch, which results in anisotropic compression of the emitting core.

This modifies the structures of electronic states of a  dot and thereby its  emitting properties. One implication of these changes is the realization of the regime of local charge neutrality of the emitting “exciton” state, which greatly reduces its coupling to lattice vibrations and fluctuating electrostatic environment, key to suppressing fluctuations in the emitted spectrum. An additional benefit of the modified electronic structures is dramatic narrowing of the  linewidth, which becomes smaller than the room-temperature thermal energy.

 Explore further: Sandwich structure of nanocrystals as quantum light source

More information: Young-Shin Park et al, Asymmetrically strained quantum dots with non-fluctuating single-dot emission spectra and subthermal room-temperature linewidths, Nature Materials (2018). DOI: 10.1038/s41563-018-0254-7

 

Quantum Dots and Lipid Rafts: Analytical Chemistry Solves a Nanoscale Mystery


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Article from Sustainable Nano

 

Remember all those great Black Friday deals on QLED televisions? You may not realize it, but they were all about nanotechnology!

The Q in QLED stands for quantum dots, which are not only being used to enhance the displays of TVs, but also are used in solar cells, medical imaging, and sensing.1-3 However, the disposal of these particles is not well regulated, leading to concern over their release into the environment. In the frenzy of holiday shopping, have you ever stopped to wonder what could happen if a quantum dot lands on the surface of a cell?

QLED

Figure 1. The “Q” in QLED TV stands for quantum dot (image by Samsung Newsroom)

As an analytical chemist, my mind is constantly blown by the suite of analytical tools that we have in the Center for Sustainable Nanotechnology to study really hard scientific questions like this one. I recently used two of these analytical tools, the atomic force microscope(AFM) and the quartz crystal microbalance (QCM) to tackle the tricky question about quantum dots on a cell surface. In our study, we looked at how quantum dots interact with supported lipid bilayers, which (as we explained in a previous blog post) we can use as a mimic of the cell membrane. The paper was called “Quaternary Amine-Terminated Quantum Dots Induce Structural Changes to Supported Lipid Bilayers.” 4

Q dots

Figure 2. The goal of this work was to understand the impact of quantum dots on supported lipid bilayers, which are a mimic for the outer membrane of cells. (image by Arielle Mensch)

 

Let me break down why this problem is so tricky and why it required really fancy tools to be able to study it. Everything we were studying was too small to be seen by eye or even using regular microscopes – the nanoparticles were about 6 nm and the lipid bilayers were about 4-5 nm – so we needed to use tools that allowed us to really zoom in to the nanoscale to get an idea of what was happening. Furthermore, the cell membrane of an organism is naturally wet, so we needed tools to allow us to work in liquids. Finally, the interactions between nanoparticles and membranes are dynamic, meaning they can change from moment to moment, so we really wanted to use tools that allowed us to monitor the interactions of the quantum dots and bilayers over time and not just take a single snapshot.

single image.png

Figure 3. Only capturing a single image doesn’t necessarily tell you everything you need to know about a situation… (image by Axel Naud)

 

With these requirements in mind, I set out to design a system that we could use to understand these interactions in liquid and in real time. We chose to work with supported lipid bilayers that contain something called phase-segregated domains, or “lipid rafts.” These lipid rafts are found in the cell membranes of different organisms, from plants to animals to bacteria, and are important for moving things in and out of the cell, which makes them very interesting to study. Furthermore, my collaborator, Dr. Eric Melby, previously showed that 4-nm, positively charged gold nanoparticles attached more  to supported lipid bilayers that had lipid rafts than those that didn’t (you can read more about his work here). This suggested that lipid rafts may play an important role in nanoparticle interactions with cell membranes, which was something I wanted to explore further with different types of nanoparticles, namely quantum dots.

 

lipid raft

Figure 4. We used supported lipid bilayers either with or without lipid rafts to understand the impact of quantum dots on these types of bilayers. (image adapted from Mensch et al.4 with permission from the American Chemical Society)

 

To start, I used Eric’s method of forming supported lipid bilayers either with or without lipid rafts using quartz crystal microbalance. As I’ve described previously, QCM is a very sensitive balance that uses a quartz crystal to measure changes in frequency, which we can use to figure out changes in mass. For example, if we add quantum dots to a bilayer formed on the quartz crystal and notice that the frequency starts to decrease, this tells us that the bilayer is getting heavier because the added quantum dots are sticking to it.

In my experiments, we saw that when we added quantum dots to bilayers with or without lipid rafts the frequency decreased over time (Figure 5). This told us that the quantum dots were attaching to our bilayers. Interestingly, when we rinsed the bilayer with buffer (to get rid of any loosely attached quantum dots), we first saw a decrease of mass (likely due to quantum dots leaving the bilayer) and then saw another increase in mass before the measurement leveled off. This was the first time that we had observed this type of change using QCM before. We hypothesized that this was due to the quantum dots causing some sort of restructuring of the bilayer, such as holes, multilayers, or a combination of events. But with QCM alone, we were unable to say for certain what was happening.

 

QCM.png

Figure 5. By QCM we saw that the quantum dots attached to the lipid bilayers. However, interesting frequency shifts after the rinse suggested that something more complicated was going on with these interactions. (image adapted from Mensch et al.4 with permission from the American Chemical Society)

 

Because we were uncertain what impact the quantum dots were having on the structure of the bilayer, we decided to use another analytical technique to get an actual picture of what was happening. This time we used atomic force microscopy (AFM). This technique allows us to study these interactions in liquid and over time, which if you remember were two very key factors to this work. I’ve described AFM in detail previously here, but briefly AFM works by using a very sharp tip that is attached at the end of a cantilever. We line up a laser to the end of this tip, which reflects off the tip onto a sensitive detector. As the tip scans across the sample, the laser light will move up or down on the detector depending on the height of the sample. From these changes in the laser’s position, we’re able to determine how tall features of the sample are.

 

AFM.png

Figure 6. Atomic force microscopy allows us to visualize the interaction of quantum dots and supported lipid bilayers in liquid and in real time. (image by Arielle Mensch)

 

For the first part of our AFM experiment, we formed lipid bilayers with lipid rafts. These rafts are about 1 nm taller than the other part of the bilayer. You can see this in Figure 7, where the brighter regions of the bilayer are the lipid rafts.

 

AFM lipid rafts

Figure 7. Lipid rafts within a supported lipid bilayer are ~1 nm taller than the surrounding regions of the bilayer. The 2-micrometer scale bar equals 2,000 nanometers, and the axis on the left shows you how the brightness of each region corresponds to a height in nanometers. (image adapted from Mensch et al.4 with permission from the American Chemical Society)

 

To investigate the impact of quantum dots on these bilayers, we added quantum dots to the bilayers and collected AFM images over time. This allowed us to monitor the changes to the structure of the bilayers. Figure 8 shows what we found – and it was pretty neat!

 

afm images.png

Figure 8. Sequence of AFM images showing the disappearance of lipid rafts over 15 min. The blue arrows are pointing to the lipid rafts or disappearance of lipid rafts in the images. The axis on the right shows you how the brightness of each region corresponds to a height in nanometers. (image adapted from Mensch et al.4with permission from the American Chemical Society))

 

When we added quantum dots to the lipid bilayers, the lipid rafts shrank and eventually disappeared! It only took about 15 minutes for them to completely disappear. You can see this by following the blue arrows in Figure 8. The other bright regions in the images are quantum dots binding to the bilayers and inducing structural changes (increasing the height in these regions or burrowing into the bilayer). These two changes are consistent with the mass changes we saw using QCM. We believe that the lipid rafts collapse because of an increase in energy due to the addition of the quantum dots. Basically, it is easier for the lipid rafts to mix together with the other components in the bilayer rather than stay separated.

 

Schematic

Figure 9. Schematic showing how positively charged quantum dots can cause the collapse of lipid rafts in supported lipid bilayers. (image adapted from Mensch et al.1 with permission from the American Chemical Society)

 

So, you might be wondering what all of this means. Well, to summarize, we found that positively charged quantum dots attach to supported lipid bilayers either with or without lipid rafts present. They also cause restructuring of the bilayers. In particular, when lipid rafts were present, the quantum dots actually caused the collapse of these important cell membrane components. Lipid rafts are found in the cell membranes of many different organisms, so this could have important implications in figuring out how nanoparticles affect different organisms.

But like with all good studies, there are still many more questions to explore! For this study we used supported lipid bilayers, but it would be really interesting to look at lipid rafts naturally within the cell membranes of actual organisms to see if we see the same effects. Furthermore, we can consider different types of nanoparticles with different surface coatings and see if that changes the results. So, the next time I see a QLED TV at the store, I’ll be sure to admire its beautiful colors, but I’ll also be thinking about my next research project.


ADDITIONAL RESOURCES


REFERENCES

  1. Martynenko, I. V.; Litvin, A. P.; Purcell-Milton, F.; Baranov, A. V.; Fedorov, A. V.; Gun’ko, Y. K. Application of semiconductor quantum dots in bioimaging and biosensing. Materials Chemistry B, 2017, 5, 6701−6727. doi: 10.1039/C7TB01425B
  2. Rühle, S.; Shalom, M.; Zaban, A. Quantum-dot-sensitized solar cells. ChemPhysChem2010, 11, 2290−304. doi: 10.1002/cphc.201000069
  3. Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.; Mattoussi, H. Quantum dot bioconjugates for imaging, labelling and sensing. Nature Materials, 2005, 4, 436-446. doi: 10.1038/nmat1390
  4. Mensch, A.C., Buchman, J.T., Haynes, C.L., Pedersen, J.A., Hamers, R.J. Quaternary amine-terminated quantum dots induce structural changes to supported lipid bilayers. Langmuir, 2018, 34, 12369-12378. DOI: 10.1021/acs.langmuir.8b02047

Quantum Dots leader completes deal to manufacture NextGen Cadmium Free QD’s in Asia


A leading US quantum dot and nanomaterials manufacturer has announced a licensing and manufacturing deal in Assam, India.

The company, Quantum Materials Corp (QMC), has a range of products which can be used to make anything from superior Ultra High Definition television displays to ultra-thin solar cells and more efficient batteries.

The agreement will not only lead to significant job opportunities in the locality of Assam, but is also a major step in deploying QMC’s extraordinary technologies in the region.

There is the opportunity to adopt next-generation solar photovoltaic technology in the area, after the implementation of recent tariffs on imported photovoltaics into India.

QMC’s cadmium-free quantum dots offer a less hazardous and eco-friendlier alternative for producers and consumers, providing them with the color benefit without the risks of toxicity or liability.

The incorporation of cadmium in quantum dots has restricted their adoption, keeping manufacturers from leveraging the benefits of the technology. Restriction of Hazardous Substances regulations currently state that 1,000 parts per million (ppm) cadmium can be used, however this exception will soon expire and only 100 ppm of cadmium will be acceptable. In 2015, the European Parliament banned the continued use of cadmium in display and lighting devices.

img_0866Read More: What are quantum dots? The Science and Applications

Furthermore, controls and regulations are growing in Asia, with China implementing new laws of its own.

QMC signed the License and Development Agreement with Amtronics CC to allow for the establishment of large scale, low cost quantum dot production for the development and future commercial manufacture of: ultra-high definition display panels, solid state lighting LEDs and quantum dot driven thin-film solar cells.

The Agreement provides Amtronics CC with the right to manufacture quantum dots and thin-film quantum dot solar cells for commercial supply in India, as well as the right to use the QDXTM trademark and technical data to support its marketing initiatives. Under the terms of the Agreement, QMC receives an immediate upfront license fee of US$1,000,000 in addition to technology development funding, scheduled milestone payments and royalties on all quantum dots/solar cells produced.

The 12,000 square feet nanotech-focused facility is being established as the anchor project within the recently announced Electronics Manufacturing Cluster in the Guwahati Tech City.

“We are extremely pleased to partner with Amtronics CC and Amtron as they establish the necessary infrastructure to support large scale thin-film, quantum dot based solar cell production in Assam India using QMC patented technologies” explained Stephen B. Squires, President and CEO of Quantum Materials Corp.

“India’s recent implementation of tariffs applied to imported solar photovoltaics creates an ideal opportunity to establish QMC’s next generation thin-film photovoltaics for broad adoption in the region. I am highly confident that our technologies will help India fulfill its goal to deploy low cost renewables as a significant step toward energy independence”

Dr. George Anthony Balchin, Managing Director of Amtronics CC added, “We are pleased to be involved and provide the initial US $20,000,000 in funding for this enterprise and are anxious to see these extraordinary technologies deployed in a region that will benefit from both the end product as well as the significant potential for job creation.

The initial capital infusion will be used to build out the facility, purchase all the production and process equipment, including the micro reactors, train the staff and provide the initial working capital. It is very rare and rewarding to be involved with a project that is the culmination of a group of like-minded individuals striving for a common goal that has so much potential to enhance the lives of so many.”

Commenting further QMC CEO Squires stated: “As India represents one of the largest renewable energy and consumer electronics markets in the world, our partnership with Amtronics CC is an important step in expanding the value of the QMC franchise globally. This partnership will allow us to address global challenges such as rising energy costs, energy security, increasing power consumption and environmental quality on a more rapid basis.”

Eco-friendly nanoparticles for artificial photosynthesis – Indium-based quantum dots produce clean hydrogen fuel from water and sunlight for a sustainable Energy Source


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Researchers at the University of Zurich have developed a nanoparticle type for novel use in artificial photosynthesis by adding zinc sulfide on the surface of indium-based quantum dots. These quantum dots produce clean hydrogen fuel from water and sunlight – a sustainable source of energy. They introduce new eco-friendly and powerful materials to solar photocatalysis.
Quantum dots are true all-rounders. These material structures, which are only a few nanometers in size, display a similar behavior to that of molecules or atoms, and their form, size and number of electrons can be modulated systematically. This means that their electrical and optical characteristics can be customized for a number of target areas, such as new display technologies, biomedical applications as well as photovoltaics and photocatalysis.

Fuel production using sunlight and water

Another current line of application-oriented research aims to generate hydrogen directly from water and solar light. Hydrogen, a clean and efficient energy source, can be converted into forms of fuel that are used widely, including methanol and gasoline. The most promising types of quantum dots previously used in energy research contain cadmium, which has been banned from many commodities due to its toxicity.
The team of Greta Patzke, Professor at the Department of Chemistry of the University of Zurich, and scientists from Southwest Petroleum University in Chengdu and the Chinese Academy of Sciences have now developed a new type of nanomaterials without toxic components for photocatalysis (Nature Communications“Efficient Photocatalytic Hydrogen Evolution with Ligand Engineered All-Inorganic InP and InP/ZnS Colloidal Quantum Dots”).

Indium-containing core with a thin layer of zinc sulfide

The three-nanometer particles consist of a core of indium phosphide with a very thin surrounding layer of zinc sulfide and sulfide ligands.
Schematic representation of photocatalytic hydrogen production with InP/ZnS quantum dots in a typical assay
Schematic representation of photocatalytic hydrogen production with InP/ZnS quantum dots in a typical assay. (Image: Shan Yu) (click on image to enlarge)
“Compared to the quantum dots that contain cadmium, the new composites are not only environmentally friendly, but also highly efficient when it comes to producing hydrogen from light and water,” explains Greta Patzke.
Sulfide ligands on the quantum dot surface were found to facilitate the crucial steps involved in light-driven chemical reactions, namely the efficient separation of charge carriers and their rapid transfer to the nanoparticle surface.

Great potential for eco-friendly applications

The newly developed cadmium-free nanomaterials have the potential to serve as a more eco-friendly alternative for a variety of commercial fields.
“The water-soluble and biocompatible indium-based quantum dots can in the future also be tested in terms of biomass conversion to hydrogen. Or they could be developed into low-toxic biosensors or non-linear optical materials, for example,” adds Greta Patzke.
She will continue to focus on the development of catalysts for artificial photosynthesis within the University Research Priority Program LightChEC. This interdisciplinary research program aims to develop new molecules, materials and processes for the direct storage of solar light energy in chemical bonds.
Source: University of Zurich

Using one quantum dot to sense changes in another: Applications for developing advanced electronic and photonic devices


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Scanning electron micrograph of InAs self-assembled quantum dot transistor device. Credit: Osaka University

Quantum dots are nanometer-sized boxes that have attracted much scientific interest for use in nanotechnology because their properties obey quantum mechanics and are requisites to developing advanced electronic and photonic devices.

Quantum dots that self-assemble during their formation are particularly attractive as tunable light emitters in nanoelectronic devices and for studying quantum physics because of their quantized transport behavior. It is important to develop a way to measure the charge in a single self-assembled quantum dot to achieve quantum information processing; however, this is difficult because the metal electrodes needed for the measurement can screen out the very small charge of the quantum dot.

Researchers at Osaka University have recently developed the first device based on two self-assembled quantum dots that can measure the single-electron charge of one quantum dot using a second as a sensor.

The device was fabricated using two indium arsenide (InAs)  connected to electrodes that were deliberately narrowed to minimize the undesirable screening effect.

“The two  dots in the device showed significant capacitive coupling,” says Haruki Kiyama. “As a result, the single-electron charging of one dot was detected as a change in the current of the other dot.”

The current response of the sensor quantum dot depended on the number of electrons in the target dot. Hence the device can be used for real-time detection of single-electron tunneling in a quantum dot. The tunneling events of single electrons in and out of the target quantum dot were detected as switching between high and low current states in the sensor quantum dot. Detection of such tunneling events is important for the measurement of single spins towards electron spin qubits.

“Sensing single charges in self-assembled quantum dots is exciting for a number of reasons,” explains Akira Oiwa. “The ability to achieve electrical readout of single electron states can be combined with photonics and used in quantum communications. In addition, our device concept can be extended to different materials and systems to study the physics of self-assembled quantum dots.”

Two quantum dots are better than one: Using one dot to sense changes in another
Real-time traces of the charge sensor quantum dot (QD1) current. Changes in the charge sensor current indicate the increase and decrease of electron number in the adjacent quantum dot (QD2). Credit: Osaka University

An electronic device using self-assembled quantum dots to detect single-electron events is a novel strategy for increasing our understanding of the physics of quantum dots and to aid the development of advanced nanoelectronics and quantum computing.

 Explore further: Simultaneous detection of multiple spin states in a single quantum dot

More information: Haruki Kiyama et al, Single-electron charge sensing in self-assembled quantum dots, Scientific Reports (2018). DOI: 10.1038/s41598-018-31268-x