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New Solar Cell is More Efficient, Costs Less

New Solar Cell is More Efficient, Costs Less thumbnail

The cost of solar power is beginning to reach price parity with cheaper fossil fuel-based electricity in many parts of the world, yet the clean energy source still accounts for just slightly more than 1 percent of the world’s electricity mix.

Exposed in step-like formation, layers of new photovoltaic cell harvest more of sun’s energy.

By MIT News Office

Solar, or photovoltaic (PV), cells, which convert sunlight into electrical energy, have a large role to play in boosting solar power generation globally, but researchers still face limitations to scaling up this technology. For example, developing very high-efficiency solar cells that can convert a significant amount of sunlight into usable electrical energy at very low costs remains a significant challenge.

A team of researchers from MIT and the Masdar Institute of Science and Technology may have found a way around this seemingly intractable tradeoff between efficiency and cost. The team has developed a new solar cell that combines two different layers of sunlight-absorbing material to harvest a broader range of the sun’s energy. The researchers call the device a “step cell,” because the two layers are arranged in a stepwise fashion, with the lower layer jutting out beneath the upper layer, in order to expose both layers to incoming sunlight. Such layered, or “multijunction,” solar cells are typically expensive to manufacture, but the researchers also used a novel, low-cost manufacturing process for their step cell.

The team’s step-cell concept can reach theoretical efficiencies above 40 percent and estimated practical efficiencies of 35 percent, prompting the team’s principal investigators — Masdar Institute’s Ammar Nayfeh, associate professor of electrical engineering and computer science, and MIT’s Eugene Fitzgerald, the Merton C. Flemings-SMA Professor of Materials Science and Engineering — to plan a startup company to commercialize the promising solar cell.

Fitzgerald, who has launched several startups, including AmberWave Systems Corporation, Paradigm Research LLC, and 4Power LLC, thinks the step cells might be ready for the PV market within the next year or two.

The team presented its initial proof-of-concept step cell in June at the 43rd IEEE Photovoltaic Specialists Conference in Portland, Oregon. The researchers have also reported their findings at the 40th and 42nd annual conferences, and in the Journal of Applied Physics and IEEE Journal of Photovoltaics.

Beyond silicon

Traditional silicon crystalline solar cells, which have been touted as the industry’s gold standard in terms of efficiency for over a decade, are relatively cheap to manufacture, but they are not very efficient at converting sunlight into electricity. On average, solar panels made from silicon-based solar cells convert between 15 and 20 percent of the sun’s energy into usable electricity.

Silicon’s low sunlight-to-electrical energy efficiency is partially due to a property known as its bandgap, which prevents the semiconductor from efficiently converting higher-energy photons, such as those emitted by blue, green, and yellow light waves, into electrical energy. Instead, only the lower-energy photons, such as those emitted by the longer red light waves, are efficiently converted into electricity.

To harness more of the sun’s higher-energy photons, scientists have explored different semiconductor materials, such as gallium arsenide and gallium phosphide. While these semiconductors have reached higher efficiencies than silicon, the highest-efficiency solar cells have been made by layering different semiconductor materials on top of each other and fine-tuning them so that each can absorb a different slice of the electromagnetic spectrum.

These layered solar cells can reach theoretical efficiencies upward of 50 percent, but their very high manufacturing costs have relegated their use to niche applications, such as on satellites, where high costs are less important than low weight and high efficiency.

The Masdar Institute-MIT step cell, in contrast, can be manufactured at a fraction of the cost because a key component is fabricated on a substrate that can be reused. The device may thus help boost commercial applications of high-efficiency, multijunction solar cells at the industrial level.

Steps to success

The step cell is made by layering a gallium arsenide phosphide-based solar cell, consisting of a semiconductor material that absorbs and efficiently converts higher-energy photons, on a low-cost silicon solar cell.

The silicon layer is exposed, appearing like a bottom step. This intentional step design allows the top gallium arsenide phosphide (GaAsP) layer to absorb the high-energy photons (from blue, green, and yellow light) leaving the bottom silicon layer free to absorb lower-energy photons (from red light) not only transmitted through top layers but also from the entire visible light spectrum.

“We realized that when the top gallium arsenide phosphide layer completely covered the bottom silicon layer, the lower-energy photons were absorbed by the silicon germanium — the substrate on which the gallium arsenide phosphide is grown — and thus the solar cell had a much lower efficiency,” explains Sabina Abdul Hadi, a PhD student at Masdar Institute whose doctoral dissertation provided the foundational research for the step-cell. “By etching away the top layer and exposing some of the silicon layer, we were able to increase the efficiency considerably.”

Working under Nayfeh’s supervision, Abdul Hadi conducted simulations based on experimental results to determine the optimal levels and geometrical configuration of the GaAsP layer on silicon to yield the highest efficiencies. Her findings resulted in the team’s initial proof-of-concept solar cell. Abdul Hadi will continue supporting the step cell’s technological development as a post-doctoral researcher at Masdar Institute.

On the MIT side, the team developed the GaAsP, which they did by growing the semiconductor alloy on a substrate made of silicon germanium (SiGe).

“Gallium arsenide phosphide cannot be grown directly on silicon, because its crystal lattices differ considerably from silicon’s, so the silicon crystals become degraded. That’s why we grew the gallium arsenide phosphide on the silicon germanium — it provides a more stable base,” explains Nayfeh.

The problem with the silicon germanium under the GaAsP layer is that SiGe absorbs the lower-energy light waves before it reaches the bottom silicon layer, and SiGe does not convert these low-energy light waves into current.

“To get around the optical problem posed by the silicon germanium, we developed the idea of the step cell, which allows us to leverage the different energy absorption bands of gallium arsenide phosphate and silicon,” says Nayfeh.

The step cell concept led to an improved cell in which the SiGe template is removed and re-used, creating a solar cell in which GaAsP cell tiles are directly on top of a silicon cell. The step-cell allows for SiGe reuse since the GaAsP cell tiles can be under-cut during the transfer process. Explaining the future low-cost fabrication process, Fitzgerald says: “We grew the gallium arsenide phosphide on top of the silicon germanium, patterned it in the optimized geometric configuration, and bonded it to a silicon cell. Then we etched through the patterned channels and lifted off the silicon germanium alloys on silicon. What remains then, is a high-efficiency tandem solar cell and a silicon germanium template, ready to be reused.”

Because the tandem cell is bonded together, rather than created as a monolithic solar cell (where all layers are grown onto a single substrate), the SiGe can be removed and reused repeatedly, which significantly reduces the manufacturing costs.

“Adding that one layer of the gallium arsenide phosphide can really boost efficiency of the solar cell but because of the unique ability to etch away the silicon germanium and reuse it, the cost is kept low because you can amortize that silicon germanium cost over the course of manufacturing many cells,” Fitzgerald adds.

Filling a market gap

Fitzgerald believes the step cell fits well in the existing gap of the solar PV market, between the super high-efficiency and low-efficiency industrial applications. And as volume increases in this market gap, the manufacturing costs should be driven down even further over time.

This project began as one of nine Masdar Institute-MIT Flagship Research Projects, which are high-potential projects involving faculty and students from both universities. The MIT and Masdar Institute Cooperative Program helped launch the Masdar Institute in 2007. Research collaborations between the two institutes address global energy and sustainability issues, and seek to develop research and development capabilities in Abu Dhabi.

“This research project highlights the valuable role that research and international collaboration plays in developing a commercially-relevant technology-based innovation, and it is a perfect demonstration of how a research idea can transform into an entrepreneurial reality,” says Nayfeh.

MIT News

72 Comments on "New Solar Cell is More Efficient, Costs Less"

  1. Kenz300 on Wed, 31st Aug 2016 1:27 pm 

    Watch The Climate Change Ad Fox News Didn’t Want Its Viewers To See

    The impacts of climate change will affect all of us…….and all future generations……….

    We all need to begin to change our life styles and embrace the future of clean alternative energy sources like wind and solar along with electric vehicles……….

  2. Davy on Wed, 31st Aug 2016 1:54 pm 

    Clog, you are critisisizing American cities when your dear Europe is full of failing cities and a failing federation of unlike nations. I would much rather be here than there. Good luck on your Eurodrain game. P.S we are not going to save your ass a 3rd time, lol.

  3. Brat on Wed, 31st Aug 2016 3:01 pm 

    America never “saved our ass”, but instead added western Europe to its empire. Which was the intention of the US deep state behind Roosevelt from day 1 of his presidency.

  4. Davy on Wed, 31st Aug 2016 3:22 pm 

    Well, I wrote that PS to irritate the revisionists that are replete on this board. I am not sold on the idea. Too many lose ends to offer a coherent thesis. I will also say I could give a shit. Europe is a loser continent that has fucked it’s world up and the entire world in the process. The US deep state would never have had an opportunity if the Europeans where a competent people that could live together without bloodshed. The US continued that wrecking process post WWII and now China is finishing it off. What matters to me is going forward and there is not much future for the US deep state. I care about my local now not the global. The global is great to talk about but a lost cause.

  5. Apneaman on Wed, 31st Aug 2016 3:24 pm 

    Brat, it wasn’t just merica who saved your ass and the alternative to it would have been the Iron Curtain extending 200 nautical miles off the west coast of GB. Would y’all have prefered to live under that commie boot for the last 3 – 4 generations? Tell yourself.

  6. Davy on Wed, 31st Aug 2016 3:32 pm 

    Brat, you probably feel there was never a holocaust either right? That usually goes with the WWII revisionist meme. I do not buy into the US won the war. Russia with the US help won the war if resources and lives are considered. That was in Europe too not the Pacific. There would not have been a WWII if Stalin was not so incompetent from the get go. Now that I think of it that would be a great revision. Stalin wanted the Nazi’s to role over most of European Russia so he could have his Iron -Curtain. How is that Brat?

  7. Brat on Wed, 31st Aug 2016 3:50 pm 

    “Brat, it wasn’t just merica who saved your ass and the alternative to it would have been the Iron Curtain extending 200 nautical miles off the west coast of GB. Would y’all have prefered to live under that commie boot for the last 3 – 4 generations? Tell yourself.”

    America was in short term indeed the lesser evil. But in 2016 I would prefer to have been more like Hungary, which is still a 100% Hungarian nation, in contrast to West-European nations.

    But what modern Westerners don’t understand due to incessant US propaganda is that the USA and USSR were on the same side since 1933 until 1945. And if you concentrate on the fatal summer of 1939 and focus on London, you will conclude that Roosevelt and Stalin were secretely coordinating their moves via Churchill to get the war in Europa started, using Poland as useful idiot.

  8. ghung on Wed, 31st Aug 2016 4:03 pm 

    Brad said; “I would prefer to have been more like Hungary”

    Not sure how old you are, Brad, but I studied in Hungary in 1974. We took the train from Vienna to Budapest, and I remember the border crossing very well, and the change in peoples’ attitudes, their way of doing things, how they talked and what they were able to say to us. I remember the change in scenery. Wonderful folks, the Hungarians, but they didn’t smile much.

    I doubt you would have preferred it.

  9. ghung on Wed, 31st Aug 2016 4:10 pm 

    This article was on solar cells. Seems every thread gets diverted to the same bullshit topic, usually by total assholes like Clogg.

    My apologies for jumping in off topic. I was being a total asshole.

  10. Brat on Wed, 31st Aug 2016 4:50 pm 

    @Davy – Stalin was not incompetent, it was him who lured Hitler into the trap known as non-agression agreement, giving Hitler the false impression that he fould intervene in Poland without having to fear a two-front war.

    America, or its deep state rather, was the real winner of WW2 as it saw itself catapulted into global pole position and the intended American century could begin. Stalin considered himself the loser of WW2 because he failed to reach the Atlantic and knew that the USSR would fail to achieve global domination with its inferior planeconomy. Stalin had made only one mistake: not expecting that Hitler would not wait for Stalin to strike first, but instead would strike himself first. That alone enabled the enormous initial German gains and created the time for the Americans to carry out their invasion and gain a foothold in Europe and meet the Soviets halfway.

    P.S. I am open minded regarding the holocaust. But the idea we are going to accept the result of a trial that was for 75% staffed by Jews, without verification, that is unacceptable.

    P.S2 Brat=Cloggie. Sorry for the mixing, different tablet, leftover from Summer holiday.

  11. Brat on Wed, 31st Aug 2016 4:59 pm 

    @ghung – I was in 1974 in Budapest as well and had similar experiences. I obviously would not have wanted to experience that. I said that in 2016, that is in hindsight, I would have prefered a similar history, without actually having to have to go through it.

    It is obvious that you as a Brit feel very uncomfortable with these discussions, because you can only loose with them. The truth of WW2 is buried under a pile of lies, but in the end it will surface anyway.

    Isn’t the internet wonderful?

    But feel free to discuss solar cells. All ears.

  12. ghung on Wed, 31st Aug 2016 5:26 pm 

    Brat said; “It is obvious that you as a Brit feel very uncomfortable with these discussions, because you can only loose with them.”

    Wrong on both counts.

    I’m not a Brit, and I don’t feel uncomfortable with these discussions; can’t lose them because I’m not trying to win or lose. People who choose to revise their history, or the history of others will do so without my participation. I consider it a waste of time. I view history in deep time; humans repeating the same mistakes and claiming victory for millennia. In our short future, we’ll all be losers, and who’s to blame won’t matter much. You “blamers” need to grow-the-fuck-up and start figuring out where YOU will go from here. History is changing in a big way and doesn’t give a shit about your petty discussions about who did what when.

    Your obsessions are useless and irrelevant. All they do is hinder useful discussion, and display your smallness-of-mind. It’s a fucked-up way to waste a life, IMO, but if you want to let your anger over things neither of us had anything to do with consume you, go for it.

    Got it? Need any clarification? There will be no winners; only those who survive longer than those who don’t.

  13. Davy on Wed, 31st Aug 2016 6:55 pm 

    Damn, well said Ghung.

  14. Apneaman on Wed, 31st Aug 2016 8:51 pm 

    deep time

    3.7-billion-year-old fossils may be the oldest signs of life on Earth

  15. Rick Bronson on Wed, 31st Aug 2016 11:07 pm 

    The cheapest solar power tender set in Dubai, UAE at 2.99 cents / KWh is broken in just few months by Chile at 2.91 cents / KWh. Neither Natgas nor Coal can compete at this price.

  16. Cloggie on Thu, 1st Sep 2016 5:25 am 

    Currently hundreds if not thousands work groups exist that are working around the clock to improve PV-technology and news like this can be expected on a regular basis during th coming decades.

    My gut feeling is that this type of cell might be useful in densely inhabited places like cities for individuals with more money than m2.

    But if you want to set up huge PV-power plants, it should preferably be done in deserts where m2 costs nothing, with lower cost panels with less than optimal efficiency.

  17. Davy on Thu, 1st Sep 2016 6:52 am 

    This is great news. I am very hopeful we get more of this built out before other circumstances conspire to end these kinds of solar successes or greatly reduce these efforts. We are near an economic depression that will morph into an economic collapse. These solar successes will not survive this type of economic collapse process at the level needed to be revolutionary. When demand is destroyed there will be plenty of already built out power to fill the reduced supply needs.

    The above reference to a solar success is a deceptive way to highlight the cheapest power. This is a market price. What is the real price of this solar equipment and the installation? SunEdison has been in the news recently for being near bankruptcy. Does that not tell you something? Coal and NatGas are unnaturally low in relation to the power they produce and costs. This is further skewed because the real cost of fossil fuels is the carbon and the environmental damage. This is the distortions of the market and they warp people’s idea of cost by referencing market price. These installations have a return period. They are being financed in an ultra-low rate environment currently. It is these kind of variables that distort the true cost and usefulness that are warping our idea of what we can do and what is coming.

    It is my hope we see a massive effort with alternatives of all kinds especially filling up those sweet spots where they will be the most useful. Some of the sweetest of sweet spots is over our heads. We need to massively increase end user installations that may or may not be grid tied. If grid tied they then need to be able to operate without the grid in emergencies and this means storage. This is more than the equipment it is the user. It takes the correct orientation of the user to use these systems. Maintenance of batteries and understanding of loads and optimal load periods is important.

    I am all for the continuation of low cost solar installation for whatever reasons and however we can get it done. This is great news but we should not twist these results giving the wrong impression. The same is true of renewables and what they can do to reduce carbon. If we are pursuing renewables thinking we can live a typical high complexity and highly energy intensive lifestyle and still reduce carbon we are again fooling ourselves. In the end there are tradeoffs and consequences. Full lifecycle is always different than what is advertised. The real results are always manipulated by deceptive marketing. Modern life is one big deception of human’s bargaining and fooling themselves. Solar has become a prime example of this. I see misunderstandings and deception everywhere I look.

    In the case of renewables this is OK because if we are going to continue to try to maintain the status quo by whatever means good or bad I want the better. Renewables are better because they give us options and they give us resilience. All our eggs in one basket with fossil fuels is a poor choice. Renewables will only buy us time. There is no solid evidence they will be the great revolution claimed. Scaling in the time needed to beat oil depletion is not there. The physical ability of renewables is not there. They don’t represent a power source that can run a society and replicate themselves. They are not a game changer. They are an extender and a great salvage source for a society that will pop up post global and postmodern. We just can’t run the status quo on them but we can extend the status quo maybe buying us some time.

  18. Sissyfuss on Thu, 1st Sep 2016 10:13 pm 

    A bit of irony, my Amish neighbors, and there are many,are putting up small solar panels on their barns and houses for what exact purpose I haven’t inquired about yet. Makes me feel retarded that I don’t even have a solar hot water heater yet. But I am sticking close to them when the SHTF.

  19. Davy on Fri, 2nd Sep 2016 7:05 am 

    We have Amish and Mennonite around here. I have purchased several books on them and when a documentary comes along watch them. I admire them from a doom and prep point of view. Their culture is interesting from the view point of technology. It is not that they are against the introduction of technology or use of technology, they are against the disruption to their community by anything new. These disruptions includes activities and lifestyles. There is other technology they have embraced especially in their actual farm and craft operation. It was agreed upon by the community elders as to have merit and support to their community. That is enlightenment something we lack.

    There is much we can learn from the Amish of course from the side of sustainability and resilience but their ability to question technology is the greatest. It is attitudes that always trump technology. We need only look to motivated small armies that defeat great armies to realize this. I say that with a sigh because I think it is already too late for us to learn from the Amish on how to critically evaluate technology into our culture. We have already embraced everything. We have already completely embraced a global liberal democracy mixed with market capitalism for the most part. Basically in our global culture anything goes. Here and there we have controls of various kinds but really it is wide open. We have allowed the markets and individual right to trump what is best for our civilization. Part of this is the acknowledgement that we are a global world in a competitive cooperative civilization of multiple nations locked into a system of survival. We are beyond self-control we are a self-organizing cancer of uncontrolled primitive wants.

    What we can learn from the Amish today is humility. That humility is they were right and we were wrong. We have chosen the path of failure as a modern people. It is those cultures that are generally non-conformist and small that have rejected modern civilization that are the success story. We the moderns have destroyed everything in our wake. We have destabilized our climate, initiated the 6th extinction, and destroyed our many and varied cultures. Humility would be embracing reconciliation to these other cultures that did not embrace technology, complexity, and efficiency at all cost. If we would do this as a global people we could at least take some steps to adapt and mitigate to forced decline, decay, and deflation. These three D’s represent the end of affluence and the die off of a global population.

    I would love to know why the Amish are embracing solar technology but I am pretty sure that it is more agreeable to their culture to be off the grid. They use batteries so I imagine this is a way to charge those batteries. Anything that can separate them from our destructiveness I am sure is a plus. We are a plague species both physically and culturally. We coopt all. We coopt cultures insidiously by offering them options. Once our options are adopted they destroy the basics of the community. People don’t realize it but the many and varied cultures of the Native Americans were destroyed this way. They were destroyed from within. Very little occurred from actual military conquest. It was the erosion of their way of life that ended them. We beat them militarily once they were already weak. When you destroy the foundation of a culture it dies. This is exactly what we are doing to ourselves now but we can’t see it for all the lies. The glitz and shine blind us from seeing the trap. We are killing ourselves and have no clue. I am disgusted with it has I tap away on a high dollar Laptop. At least I have purchased a Scythe and other hand tools embracing that way of life the Amish have succeeded at.

  20. farmlad on Fri, 2nd Sep 2016 8:40 am 

    Davy I like to compare Amish to bow hunters. Bow hunters have some self enforced restrictions but within those perimeters they act just like all the other hunters. Just like bow hunters will spend even more money than most gun hunters so an ave amish farmer will waste vast sums of $s (my estimate of roughly $20000 per year) and natural resources to raise and maintain 8+ work horses, while their neighbor can can farm way more with a small tractor that cost $3000 and less than $1000 in fuel and maintainance per year. So that The majority of Amish can now only dream of farming for a living.

    Of course the plroblem is that they are humans like all the rest, if they would be allowed to use tractors in the fields they would not be content to stay with a small profitable farm so that would expand their community to mirror the rest of Rural America.

    So in the meantime they spend their time quibling about what is allowed and how to compete with each other and see who’s who within those parameters, and waste gobs of Money when something new is allowed in the church, say a power cart which is a diesel engine that runs the machinery that is pulled across the field by the horses. This is just an example of the laughable stupid side of the Amish.

    The reason that Solar is allowed by the amish is that electricity from the Grid has been a well established No go for a long time, so that can not be crossed to easily but Solar is in many aplications, cheaper than running their Diesel of gas generators. By the way, Amish in general don’t believe in Climate Change or worry about air pollution.

  21. Kenz300 on Fri, 2nd Sep 2016 9:46 am 

    Wind and solar continue to grow in use around the world…. driving down the cost and making them more competitive with fossil fuels……..

    Scotland blows away the competition – 106% of electricity needs from wind – joins select club

    3 Sure Signs of Texas’ Emerging Solar Market

    5 Huge Climate Success Stories 10 Years After the Release of Al Gore’s ‘An Inconvenient Truth’

    Big Oil Could Have Cut CO2 Emissions In 1970s — But Did Nothing

  22. Davy on Fri, 2nd Sep 2016 11:04 am 

    Farmlad, 1% of nothing is still nothing. My point is they may be absurd like all humans but they have something when the lights go out. We as moderns will be on their level when the grid fails but with next to nothing. We will be on their level but without something because everything we do is grid tied.

    Using modern notions of price to compare people and culture is failure. We think exceptionally that science and markets dictate the truth but what we fail to consider is science and markets also deceive. Our modern deceptions are a cultural basis. We are in the vicinity to complete ignorance of reality. The Amish are not even close.

    The Amish may be hilarious but they do not live in the degree of deception we do. Part of this is when you live simple your ability to deceive yourself is much smaller so you will naturally avoid the worst of what I call the absurd. I am not advocating Amish culture I am pointing out advantages to their attitudes.

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