Solar panels may one day be light and cheap enough to hang on a clothesline, thanks to a synthetic mineral called perovskite. Physicist Sam Stranks explains the science of solar energy and the challenges it faces.
Solar power is key to our energy future. But the solar industry is facing a conundrum: Silicon cells aren't very efficient at converting sunlight into electricity -- 29 percent efficient at best. You might wonder, why does efficiency matter so much when sunlight is free? The answer: because inefficiency means you need a lot of solar panels — which can be big, heavy and expensive to manufacture — to generate enough power to meet your needs.
But University of Cambridge physicist (and TED Fellow) SAM Stranks thinks that might change, thanks to a mineral called perovskite. He and his colleagues at Swift Solar are working hard to develop perovskite-based solar panels that could break the efficiency ceiling.
What exactly is a perovskite? The term "perovskite" refers to two substances: a perovskite oxide mineral composed of calcium titanate, and a class of compounds that share the mineral's unique crystal structure. Perovskites have such promising photovoltaic (PV) or solar power-generating properties that they are a group of man-made versions discovered by Japanese scientist Miyazakazu and colleagues in 2009. (Miyasaka was considered a potential Nobel laureate in 2018.) "These perovskites absorb sunlight better than silicon," Stranks said. "We can absorb nearly all of the sunlight with perovskite films that are 100 times thinner than silicon."
The scientists synthesized perovskites by mixing two inexpensive salts -- lead halides and organic halides. This solution forms an ink that can be applied in ultra-fine, uniform layers by inkjet printing or spin coating. "The deposited film is very thin -- about 500 nanometers, or about 1/100th the thickness of a human hair -- enough to absorb most of the sunlight needed to generate electricity," Stranks said.
The result: A little perovskite can generate a lot of power. "California, for example, needs 50 gigawatts of electricity," Stranks said. "To make enough solar panels, you only need the equivalent of half an Olympic swimming pool of perovskite ink."
另一个好处是：钙钛矿电池工厂可能比硅工厂便宜得多。硅工厂的建造成本大约在3亿美元到4亿美元之间，钙钛矿工厂的成本不到1亿美元。斯特兰克斯说：“费用的差异部分是因为制造高结晶硅需要将其加热到非常高的温度来消除缺陷。”“另一方面，钙钛矿薄膜只需要温和的加热就可以没有缺陷，而且它们可以在大型打印机上快速推出，这更具成本效益。”
虽然钙钛矿可能不会马上取代硅电池（为了了解原因，请继续阅读），但这两种化合物可以协同工作。斯特兰克斯说：“硅不是非此即彼的命题，而是两者兼而有之。”钙钛矿电池可以层叠在现有的硅太阳能电池上——在一个“串联”电池中——以提有效。斯特兰克斯认为，用钙钛矿提升硅可以使每个PV面板的效率比今天的PV面板提高20%。效率的提高会产生影响，可能会在太阳能过程中产生涟漪效应。他解释道，“如果你正在安装一栋以前需要五个面板的房子，你现在只需要四个。这改变了很多事情：太阳能发电厂的电池板会突然便宜20%，以及其他成本节约， etc.。"
这是串联电池的工作原理。太阳能电池的工作是收集可见光谱中不同波长的光——这些光被认为是不同的颜色——并将它们转化为能量。“当你在硅电池上层叠钙钛矿电池时，钙钛矿层会收集更蓝的光，这是能量最高的可见光，并将其转化为电能，”Stranks说。“其余的光然后通过下面的硅电池，硅电池吸收更红、能量更低的光线，并将其转化为电能。”这个想法是，通过这两层，你几乎收集了整个光谱，但是你顺序地这样做是为了最大化产生的能量。"
Stranks说，为什么不完全摆脱硅，只使用钙钛矿呢？这就是目标。钙钛矿-钙钛矿串联电池是斯威夫特太阳能公司团队正在开发的一项技术。钙钛矿-钙钛矿串联电池是他的联合创始人贾尔斯·埃佩隆和托马斯·莱顿斯第一次展示的一个概念。两种不同类型的钙钛矿电池放在一起，就像串联钙钛矿-硅电池收集不同频率的光一样，串联钙钛矿-钙钛矿电池也是如此。这些可能会将效率提高到35%或更高。
Why silicon still matters: We don't know how long perovskite cells will last. "Silicon cells last for 25 years, whereas perovskite cells have not been well-documented under environmental stresses like moisture and heat," Stranks said. (Remember, the material was only discovered in 2009. .) If you have an expensive solar array installed on your home, you want it to last at least a few decades. Stranks is optimistic that perovskite cells can be durable, perhaps by optimizing composition and cell design. In the meantime, tandem perovskite cells could begin to be used in transportation and communication applications that don't require long-term durability.
Perovskites could provide new customers with electricity in new forms. Stranks envisions perovskite cells one day providing electricity in rural areas of the developing world. Although silicon panels have been installed and used in a variety of environments, they can be heavy and bulky. “One idea is to roll these cheap solar panels down, fill a truck and use them in remote communities. These panels can be hung on clotheslines, installed on shelter roofs, and so on,” he said. "A typical panel, plus a battery, can power a phone charger, a lamp, or a small refrigerator." According to Stranks' best guess, it could take up to a decade for perovskites to reach consumers life. "We still have work to do and a global push is needed to realize the full potential of perovskites," he said. "But given the price of cheap clean energy, the future is bright."
