In the video below, a new technology how to build solar cells will be explained in detail.
Here some basic explanation:
Perovskite solar cell
A perovskite solar cell (PSC) is a type of solar cell which includes a perovskite-structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.[1][2] Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture.
Solar cell efficiencies of laboratory-scale devices using these materials have increased from 3.8% in 2009[3] to 25.7% in 2021 in single-junction architectures,[4][5] and, in silicon-based tandem cells, to 29.8%,[4][6] exceeding the maximum efficiency achieved in single-junction silicon solar cells. Perovskite solar cells have therefore been the fastest-advancing solar technology as of 2016.[1] With the potential of achieving even higher efficiencies and very low production costs, perovskite solar cells have become commercially attractive. Core problems and research subjects include their short- and long-term stability.[7]
Source: Perovskite solar cell, https://en.wikipedia.org/w/index.php?title=Perovskite_solar_cell&oldid=1087281604 (last visited May 12, 2022).
Video transcript:
0:00 In this video we’ll explore the world’s fastest improving new solar technology,
0:04 and provide an exclusive peek inside the lab of a team working on this breakthrough material.
0:10 Right now, while you’re watching this video, a giant fusion reactor 93 million miles away is
0:14 irradiating the earth with about as much energy as all of human civilization uses in a year.
0:19 So why aren’t we harnessing this abundant,
0:21 renewable energy source to meet all of humanity’s energy needs?
0:24 It’s not an issue of physical impossibility, “If you wanted to power the entire U.S.
0:28 with solar panels, it would take a fairly small corner of Nevada or Texas or Utah.
0:32 You only need about 100 miles by 100 miles of solar panels to power the entire United States”
0:37 Currently, only 2% of global electricity comes from solar power. And 90% of that,
0:42 comes from crystalline silicon-based solar panels, the dominant material technology.
0:47 While abundant, silicon has downsides related to efficiency,
0:50 manufacturing complexity, and pollution that prevent it from being an absolute no brainer.
0:57 Now what if I told you about a material that was lighter,
1:00 more efficient, and simpler to produce at a lower cost?
1:03 An inexpensive solution that can make a photovoltaic cell so thin,
1:06 that just half a cup of liquid would be enough to power a house? A solar panel so lightweight,
1:11 that it can be balanced atop a soap bubble.
1:13 Well, that folks, is known as the holy grail of solar, They’re called Perovskites,
1:18 and they might just revolutionize how humans generate energy from sunlight .
1:21 We headed to silicon valley to meet Joel Jean, the CEO of Swift Solar,
1:25 one of the leading teams working to bring Perovskite solar technology to light.
1:34 It’s a new kind of thin film technology. So you’ve probably heard of that for a long time, different
1:40 kinds of thin films have come and gone over the years. What we do here is a new kind of material.
1:44 It’s called perovskites, a new semiconductor material that absorbs light really effectively,
1:48 also transports charge. So it just turns out to be very efficient material for solar cells.
1:53 Solar cell technologies can be classified into two categories, wafer-based or thin-film cells.
1:58 Wafer-based cells are fabricated on semiconducting wafers,
2:01 and are usually protected by a material like glass. These are the crystalline
2:04 silicon cells you’ll typically find on bulky roof mounted solar panels.
2:08 Thin-film cells are made by depositing thin layers of semiconducting films onto a glass, plastic,
2:13 or metal substrate, and use 10 to 1000 times less material than crystalline silicon cells.
2:18 These thin-film cells are light and flexible, but have lower average efficiencies.
2:22 You can make thin film cells from amorphous silicon, or more complex
2:25 materials like Cadmium Telluride, but scientists have been on the hunt for
2:29 better thin-film solar technologies that can see more widespread use.
2:32 These materials are known as “emerging thin films”
2:36 Currently, Perovskites are the leading contender.
2:39 What could you do with a solar panel with 100 times
2:41 the power-to-weight performance of conventional silicon panels?
2:44 A solar material so abundant, it could be painted on skyscrapers.
2:48 Flexible, lightweight, highly efficient cells could open up a wide
2:51 range of applications where traditional silicon cells are too heavy and rigid.
2:55 But before we cover your Tesla model S plaid in perovskite solar,
2:59 what exactly is this revolutionary crystal?
3:02 The Perovskite crystal structure was first discovered as the naturally
3:05 occurring mineral calcium titanium oxide.
3:08 But the Perovskites used in solar cells don’t need to be mined from the earth.
3:11 A perovskite is any material with a crystal structure following the formula ABX3.
3:16 Where ‘A’ and ‘B’ are two positively charged ions, often of different sizes,
3:20 and X is a negatively charged ion.
3:22 Scientists realized that they could create a diverse range of man made perovskite crystals,
3:27 following this same arrangement, that have very useful properties.
3:30 So we use basic, you know, metal halide salts, so things like lead iodide or some some organic
3:38 salts as well. And we combine them to make these inorganic organic,
3:43 hybrid perovskites. So if you can form them in solution, you can form them out of,
3:48 in vacuum out of vapor phase. And they condense into forming these perovskite crystals.
3:53 And the thin films, they’re like multi-crystalline, which means that
3:56 there’s a bunch of little crystal domains, they turn out just to be really good semiconductors.
4:01 So just how efficient are perovskite solar cells?
4:05 The most efficient modern silicon solar panels you’d find on a home only work at best around 20%
4:10 efficiency, but the theoretical conversion efficiency of single junction solar technologies
4:15 is about 33%, called the Shockley-Queisser limit.
4:18 That’s the fundamental limit for a single solar cell singles
4:22 material based solar cell. Perovskites are the exact same thing. Silicon,
4:25 perovskites, cadmium telluride, CIGS, all of these technologies have the same limit.
4:29 But perovskite solar cells can be made in a form factor that’s capable of
4:33 much higher efficiency limits, pushing the boundaries of possibility for solar power.
4:37 To understand why perovskites hold an advantage over traditional silicon solar cells,
4:41 let’s first do a basic refresh of how photovoltaic cells convert sunlight to electricity.
4:47 The top and bottom parts of a solar cell contain semiconductor
4:50 materials with different electrical properties.
4:52 In a traditional silicon cell for example, silicon is used for both layers, but each layer is
4:57 modified or “doped” with tiny amounts of different elements to create different electrical charges.
5:01 The portion that contains a higher concentration of free negatively-charged electrons is called
5:05 the n-type region, and the side that contains more positively charged holes,
5:09 or missing electrons, is known as the p-type region.
5:12 The boundary between these two layers is known as the p-n junction. When an n-type and a p-type
5:16 material are put in contact, free electrons from the n-type material and free holes from the p-type
5:21 material move across the boundary and cancel each other out. The electrons fill in the holes.
5:26 This uncovers the fixed positive and negative charges of the dopant ions, which creates a
5:30 built-in electric field that stops more electrons and holes from moving across the boundary. This
5:35 electric field corresponds to a built-in voltage and acts like a one-way valve for charge carriers.
5:40 The fundamental unit of light is the photon, which represents the
5:43 smallest packet of electromagnetic radiation of a given wavelength.
5:47 When a photon from sunlight hits a solar cell and gets absorbed,
5:50 it creates an extra free electron and hole, which are separated by the electric field
5:54 and pulled to opposite sides of the cell. This creates a photocurrent.
5:58 If electrodes are attached to both sides of the cell,
6:00 forming an electrical circuit, an electric current will flow as long as the sun is shining.
6:06 The magic of perovskite crystals lies in their customizability.
6:10 Single junction solar cells can only absorb a portion of the solar spectrum
6:13 depending on what semiconductor material they use.
6:15 The lowest energy of light that can be absorbed in a semiconductor is called its band gap.
6:20 A semiconductor will not absorb photons of energy less than the band gap;
6:23 and the useful energy that can be extracted from a photon is no more than the band gap energy.
6:28 This means much of the energy in sunlight goes to waste when it hits a single junction solar cell,
6:32 but because the band gap of perovskites can be easily changed, you can stack perovskite layers
6:37 on top of each other that are chemically tuned to absorb different parts of the solar spectrum.
6:41 This results in a solar cell with multiple p-n junctions that can produce electricity
6:45 from a broader range of light wavelengths or extract more energy from each photon,
6:49 improving the cell’s efficiency.
6:51 So when you stack two solar cells on top of each other, that’s called a tandem,
6:55 or a multi junction solar cell. And when you do that,
6:58 that actually pushes that efficiency limit up from 30% to over 40, about 45 and 46%
7:04 Theoretically, an infinite number of junctions would
7:06 have a limiting efficiency of 86.8% under highly concentrated sunlight.
7:11 and it goes higher with more layers, but it also becomes more expensive and you get
7:14 diminishing returns. So generally, we talked about doing two layers or making a tandem,
7:19 and that that’s kind of the the real selling point of perovskites.
7:22 So perovskite tandems convert more of the sun’s energy into electricity, rather than
7:26 wasting it as excess heat. So what are the exact efficiency percentages we’re talking about here?
7:32 we shouldn’t expect solar cells above 40% efficiency,
7:35 this kind of solar cell for a long, long time. I think in theory, it could get there. But
7:38 realistically I think in the 30’s is is doable, which is still a substantial jump from,
7:44 you know, what you see out there on the market today
7:46 It’s not just performance that’s improved. The
7:48 nature of Perovskites allow for manufacturing advantages too.
7:51 So you only need less than 1% of this material that you need for a silicon cell
7:56 to absorb all the sunlight. So in theory, you can save money, you can basically make this
8:00 stuff a lot cheaper. The cool thing about the perovskites is that they turn out even though
8:05 it’s made of this kind of not perfect material, you can actually make a very, very efficient solar
8:09 cell. It’s formed at low temperatures. Silicon, usually you have to crystallize that something
8:13 like 1400 degrees Celsius, with perovskites, you can form it at less than 100 degrees Celsius.
8:19 So that means that you can actually use smaller equipment, and you can kind of use
8:23 more standard chemical processes. And you can form the solar cells on things like plastics,
8:28 so things that would melt under high temperatures you can actually
8:30 use to make solar cells on. So you can make something really lightweight and flexible as well.
8:35 Perovskite Thin films can be made by synthesizing a solar ink of sorts, and gently heating it until
8:40 the perovskites crystallize, just like salt crystals emerging from evaporating sea water.
8:45 Now let’s go deeper into the lab, to take a rare and exclusive sneak
8:48 peak behind the scenes to see how Perovskite solar cells are made.
8:52 Yeah, so this guy is called a thermal evaporator. So it’s, it’s one of many kinds of deposition
8:57 tools that we use to, to put down thin films. So when you look at a perovskite solar cell,
9:02 it’s like any other thin film device like an organic LED, or a cadmium telluride solar cell,
9:07 it’s got a lot of thin film semiconductor layers. And one of the ways you deposit some
9:10 of those layers, is using techniques like thermal evaporation, where you heat up a source material,
9:15 maybe it’s silver, or maybe it’s a precursor for one of your semiconductors. And you melt it,
9:20 you evaporate it and then you have a cold surface that you condense on. And that cold
9:23 surface is actually just at room temperature. It’s a plastic sheet or a glass sheet,
9:27 or even a silicon wafer that you’re trying to deposit a film on.
9:30 The substrate sits at the very top of the chamber. It’s under high vacuum and you again
9:34 evaporate this material and it condenses and forms this uniform thin film and you
9:38 do that many many times with different kinds of techniques. And that gets you your solar cell.
9:42 You can also make perovskite cells with spin-coating, screen printing,
9:46 electrodeposition or even printing the material on a sheet just like an inkjet printer.
9:52 Here is the end result, a small rectangular perovskite solar cell.
9:55 So this is the side that’s facing the sun, correct, and this is the back of the cell?
10:00 Yeah, the side facing the sun is actually you’re looking through the glass. And on the other side
10:05 of that glass, there’s a perovskite layer, kind of sandwiched between the contacts. So the contacts
10:11 are, what pull the charge out of the perovskite. So there’s a transparent conductor on that on the
10:16 close the side closest to us. Then there’s the perovskite. And then on the other side,
10:21 if you look at it from you know, from the backside, there’s these silver electrodes.
10:25 It can be any different kinds of metals. But that side doesn’t have to be transparent because you
10:29 actually want the light to reflect back into the semiconductor not go through.
10:33 These solar cells are just lab samples designed to test different perovskite formulas.
10:38 And you can see that these different pads, each of these squares is a solar cell.
10:43 So we have six different solar cells on one substrate for for r&d purposes, for testing.
10:48 Swift solar is trying to create a perovskite solar
10:51 cell with the perfect mix of longevity and efficiency ready for commercialization.
10:55 So how do you test the cells if it’s a cloudy day? The sun can be quite unreliable,
10:59 even in California.
11:00 We actually use this, this machine right here. So this is a it’s a, it’s called a solar simulator.
11:04 So it’s actually just a fake sun. It’s it’s an LED array that basically has all the colors basically,
11:11 it has a lot of different colors of LEDs something like 20 Different
11:14 LED colors in an array with optics to make it really uniform. So the idea is here we don’t want
11:19 to have to take our solar cells outdoors and test you know if it’s raining we can’t test our cells.
11:24 what are these here. Are these the circuit boards that the solar panels,
11:27 that measure the voltage and the solar panel sit on top of them?
11:29 Yeah, measure the voltage and current. So this is you can kind of see this, it’s the same shape
11:33 and it’s got a bunch of pads on there. And each of those like are basically leads to pull out current
11:38 or measure. yeah, to measure voltage, so or apply voltage. So you can see we can do 20 of these at
11:43 once. And it basically automatically moves around to test the cells, each of them individually.
11:50 Perovskites have improved greatly since scientists first began testing them, and are now beginning
11:55 to surpass mono and poly crystalline silicon cells in conversion efficiency.
11:59 As perovskites start coming into commercial usage, where are we most likely to see them first?
12:04 All the traditional solar applications. On your rooftop, out in the field somewhere,
12:07 in the desert, on commercial rooftops, on residential rooftops, like those are all fair game
12:11 down the line. Perovskites aren’t ready for that kind of, you know, primetime yet, the stability is
12:17 still challenged, like you’re getting them to last for 25 years, we can’t No one can say that yet,
12:21 confidently, we don’t have the field data to prove that. So there’s a lot of engineering
12:25 work and science to be done to get to that point. But there’s a lot of applications where you don’t
12:30 need 25 year life, right, like a car maybe only needs 10 or 15 years. There’s things like high
12:34 altitude drones, right, which are going to be fully powered by solar, you know, they’re flying
12:38 the stratosphere at 65,000 feet beaming down internet. So that kind of thing is needs very,
12:43 very lightweight solar needs very efficient solar, it doesn’t need to a 25 year life, you maybe only
12:47 need a couple years, five years. So that kind of thing you can imagine being powered by perovskites
12:53 very soon, same with solar wristwatches or small IoT Internet of Things, devices. A lot
12:59 of these kinds of mobile applications where you can imagine perovskites kind of coming into the
13:03 market and then eventually improving towards the rooftop, towards the utility scale applications.
13:09 So what exactly are the challenges that are preventing perovskites
13:12 from dominating the solar energy landscape, and changing everything?
13:16 we’ve spent a lot of time in this lab actually working on the challenges of developing this
13:20 technology to a point where it’s ready for, for production and for scale up. There’s things like
13:25 stability, which is probably the core problem for perovskites is, how do you make these cells
13:30 last effectively, for years in the field, under high temperatures, a car roof might get up to 80
13:35 degrees Celsius, right or more on a hot day. So you need to be able to like survive those
13:39 temperatures for years at a time. And I think we tried to do we do a lot of tests to and iteration
13:43 on the materials on the device stack, the stack of materials we use on the design of the device
13:48 itself on the packaging, to make sure that we can survive those kinds of temperatures,
13:53 high humidities, the different kinds of environments you face outdoors.
13:57 The relative fragility of the perovskite material requires protection to shield this semiconductor
14:02 layer from environmental stresses and degradation.
14:04 The international standards for terrestrial solar
14:06 panels require harsh testing that simulates 25 years of being outside.
14:10 In these tests panels are heated up and even battered with simulated hailstones.
14:15 The problem with perovskites is that they’re still relatively new. We can subject them to these
14:19 harsh simulated tests that give us a pretty good idea of their longevity, but we just don’t have
14:23 the real world data yet like we do for silicon panels, which have been in use for decades now.
14:28 While perovskites are still in the research & development phase of the technology life cycle,
14:33 there are many teams all over the world working on
14:35 improving their efficiency and stability to bring them into commercial adoption.
14:39 The raw materials for perovskites are abundant around the world,
14:42 and the solar cells can be made using relatively simple manufacturing processes.
14:46 This means that Perovskites can rapidly scale when they’re ready for mass market commercialization.
14:51 It’s estimated that Perovskite panels could cost up to 15 times less per
14:54 watt than modern commercial silicon solar panels.
14:57 In addition, engineered perovskite materials absorb all parts of the solar spectrum
15:01 efficiently to produce the highest possible power output and Ultra-thin films open the
15:05 door to new product formats with unprecedented power-to-weight ratios and high flexibility.
15:12 A future with cheap, abundant solar power could open the door for a variety of use
15:16 cases where current photovoltaic technology does not yet make sense.
15:20 How about these electric yachts I’ve filmed for previous Electric Future videos. Their range could
15:24 be radically improved with higher efficiency, lightweight, integrated perovskite solar panels.
15:29 We could see integrated Solar panels on trucks, buses and cars and any other
15:32 applications where sunlight is not yet considered energy-dense enough to provide meaningful power.
15:37 Imagine buildings covered in transparent
15:39 photovoltaic glass windows that generate electricity.
15:44 It’s difficult to predict the future of solar. While perovskites are promising, serious
15:48 researchers avoid playing favorites. Instead, they view all technologies objectively based on
15:53 increased efficiency, reduced materials usage, and reduced manufacturing complexity and cost.
15:59 Solar photovoltaics are the fastest-growing energy technology in the world today and a leading
16:04 candidate for terawatt-scale, carbon-free electricity generation in our lifetime.
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16:11 it’s important to first learn the fundamentals of solar energy.
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