Ultrathin, Lightweight Solar Panels

A race is on in solar engineering to create almost impossibly-thin, flexible solar panels. Engineers imagine them used in mobile applications, from self-powered wearable devices and sensors to lightweight aircraft and electric vehicles. Against that backdrop, researchers at Stanford University have achieved record efficiencies in a promising group of photovoltaic materials. Chief among the benefits of these transition metal dichalcogenides – or TMDs – is that they absorb ultrahigh levels of the sunlight that strikes their surface compared to other solar materials.

Transition metal dichalcogenide solar cells on a flexible polyimide substrate

Imagine an autonomous drone that powers itself with a solar array atop its wing that is 15 times thinner than a piece of paper,” said Koosha Nassiri Nazif, a doctoral scholar in electrical engineering at Stanford and co-lead author of a study published in the Dec. 9 edition of Nature Communications. “That is the promise of TMDs.”

The search for new materials is necessary because the reigning king of solar materials, silicon, is much too heavy, bulky and rigid for applications where flexibility, lightweight and high power are preeminent, such as wearable devices and sensors or aerospace and electric vehicles.

Silicon makes up 95 percent of the solar market today, but it’s far from perfect. We need new materials that are light, bendable and, frankly, more eco-friendly,” said Krishna Saraswat, a professor of electrical engineering and senior author of the paper. While TMDs hold great promise, research experiments to date have struggled to turn more than 2 percent of the sunlight they absorb into electricity. For silicon solar panels, that number is closing in on 30 percent. To be used widely, TMDs will have to close that gap.

The new Stanford prototype achieves 5.1 percent power conversion efficiency, but the authors project they could practically reach 27 percent efficiency upon optical and electrical optimizations. That figure would be on par with the best solar panels on the market today, silicon included.

Moreover, the prototype realized a 100-times greater power-to-weight ratio of any TMDs yet developed. That ratio is important for mobile applications, like drones, electric vehicles and the ability to charge expeditionary equipment on the move. When looking at the specific power – a measure of electrical power output per unit weight of the solar cell – the prototype produced 4.4 watts per gram, a figure competitive with other current-day thin-film solar cells, including other experimental prototypes. “We think we can increase this crucial ratio another ten times through optimization,” Saraswat said, adding that they estimate the practical limit of their TMD cells to be a remarkable 46 watts per gram.”

Source: https://news.stanford.edu/

Carbon Dots from Human Hair Boost Solar Cells

In a study published in the Journal of Materials Chemistry A, the researchers led by Professor Hongxia Wang in collaboration with Associate Professor  Prashant Sonar  of the Queensland University of technology  (QUT) in Australia  showed the carbon nanodots could be used to improve the performance of perovskites solar cells, a relatively new photovoltaic technology, are seen as the best PV candidate to deliver low-cost, highly efficient solar electricity in coming years. They have proven to be as effective in power conversion efficiency as the current commercially available monocrystalline silicon solar cells, but the hurdles for researchers in this area is to make the technology cheaper and more stable. Unlike silicon cells, they are created with a compound that is easily manufactured, and as they are flexible they could be used in scenarios such as solar-powered clothing, backpacks that charge your devices on the go and even tents that could serve as standalone power sources.

This is the second major piece of research to come as a result of a human hair derived carbon dots as multifunctional material. Last year, Associate Professor Prashant Sonar led a research team, including Centre for Materials Science research fellow Amandeep Singh Pannu, that turned hair scraps into carbon nanodots by breaking down the hairs and then burning them at 240 degrees celsius. In that study, the researchers showed the carbon dots could be turned into flexible displays that could be used in future smart devices.

In this new study, Professor Wang’s research team, including Dr Ngoc Duy Pham,  and Mr Pannu, working with Professor Prashant Sonar’s group, used the carbon nanodots on perovskite solar cells out of curiosity. Professor Wang’s team had previously found that nanostructured carbon materials could be used to improve a cell’s performance. After adding a solution of carbon dots into the process of making the perovskites, Professor Wang’s team found the carbon dots forming a wave-like perovskite layer where the perovskite crystals are surrounded by the carbon dots.

It creates a kind of protective layer, a kind of armour,” Professor Wang said. “It protects the perovskite material from moisture or other environmental factors, which can cause damage to the materials.”

The study found that perovskite solar cells covered with the carbon dots had a higher power conversion efficiency and a greater stability than perovskite cells without the carbon dots.

Source: https://www.qut.edu.au/

Perovskite Solar Panels Go To The Market

Across the globe, a clutch of companies from Oxford, England to Redwood City, Calif. are working to commercialize a new solar technology that could further boost the adoption of renewable energy generation. Earlier this year, Oxford PV, a startup working in tandem with Oxford Universityreceived $3 million from the U.K. government to develop the technology, which uses a new kind of material to make solar cells. Two days ago, in the U.S., a company called Swift Solar raised $7 million to bring the same technology to marketaccording to a filing with the Securities and Exchange Commission.

Called a perovskite cell, the new photovoltaic tech uses hybrid organic-inorganic lead or tin halide-based material as the light-harvesting active layer. It’s the first new technology to come along in years to offer the promise of better efficiency in the conversion of light to electric power at a lower cost than existing technologies.

Perovskite has let us truly rethink what we can do with the silicon-based solar panels we see on roofs today,” said Sam Stranks, the lead scientific advisor and one of the co-founders of Swift Solar, in a Ted Talk. “Another aspect that really excites me: how cheaply these can be made. These thin crystalline films are made by mixing two inexpensive readily abundant salts to make an ink that can be deposited in many different ways… This means that perovskite solar panels could cost less than half of their silicon counterparts.”

First incorporated into solar cells by Japanese researchers in 2009, the perovskite solar cells suffered from low efficiencies and lacked stability to be broadly used in manufacturing. But over the past nine years researchers have steadily improved both the stability of the compounds used and the efficiency that these solar cells generate.

Oxford PV, in the U.K., is now working on developing solar cells that could achieve conversion efficiencies of 37 percentmuch higher than existing polycrystalline photovoltaic or thin-film solar cells.

New chemistries for solar cell manufacturing have been touted in the past, but cost has been an obstacle to commercial rollout, given how cheaply solar panels became thanks in part to a massive push from the Chinese government to increase manufacturing capacity.

Source: https://techcrunch.com/