Perovskite semiconductors for solar photovoltaic cells

Progress On Perovskite Solar Cells | Earth Wise with Randy Simon​

Perovskites are semiconductors with a specific crystal structure. Their properties make them well suited for making solar cells. They can be manufactured at room temperature, using much less energy than it takes to make the silicon-based solar cells widely used today. As a result, perovskite solar panels would be cheaper and more sustainable to produce. Manufacturing silicon solar cells takes a lot of energy because silicon is forged at around 3000 degrees Fahrenheit. In addition, perovskites can be made flexible and transparent, making it possible to use them in ways unavailable with silicon solar technology.​

But unlike silicon, perovskites are very fragile. The early solar cells made from perovskites in 2009 and 2012 lasted for only minutes. Lots of potential, but little practicality.

Recently, Princeton Engineering researchers have developed the first perovskite solar cell with a commercially viable lifetime, which is a major breakthrough.

berkeman said:

** Where does the name Perovskite come from?

berkeman said:

what was the breakthrough that made the fabricated solar cells so much more robust compared to the initial ones that were so fragile?

Xiaoming Zhao, a postdoctoral researcher in Loo’s lab in the Andlinger Center for Energy and the Environment, had been working on a number of designs with colleagues. The efforts layered different materials in order to optimize light absorption while protecting the most fragile areas from exposure. They developed an ultra-thin capping layer between two crucial components: the absorbing perovskite layer and a charge-carrying layer made from cupric salt and other substances. The goal was to keep the perovskite semiconductor from burning out in a matter of weeks or months, the norm at that time.

It’s hard to comprehend how thin this capping layer is. Scientists use the term 2D to describe it, meaning two dimensions, as in something that has no thickness at all. In reality, it’s merely a few atoms thick — more than a million times smaller than the smallest thing a human eye can see. While the idea of a 2D capping layer isn’t new, it is still considered a promising, emerging technique. Scientists at NREL have shown that 2D layers can greatly improve long-haul performance, but no one had developed a device that pushed perovskites anywhere close to the commercial threshold of a 20-year lifetime.

Zhao and his colleagues went through scores of permutations of these designs, shifting minute details in the geometry, varying the number of layers, and trying out dozens of material combinations. Each design went into the light box, where they could irradiate the sensitive devices in relentless bright light and measure their drop in performance over time.

" It is worth highlighting that real-world operating conditions vary by geographic location and mounting conditions. For example, a module may occassionally experience 85°C in Saudi Arabia, with a time-averaged temperature of up to 55°C, whereas the climate conditions will be much more benign in temperate regions such as Germany, where there are fewer extreme temperature spikes and an average temperature well below 35°C."

Perovskite (CaTiO₃) has an orthorhombic structure (space group Pbnm). A large number of compounds with the general formula ABO₃ have the perovskite structure; in many of these, as in perovskite, A is divalent and B is tetravalent so that Ca can be partially or totally replaced by Na, Mn, Ce, Sr, Pb and Ti by Fe, Nb, Zr and Mg with the valency accommodated by paired substitution such as Fe³⁺ + Nb⁵⁺ replacing Ti³⁺.