In the race to replace silicon in low-cost solar cells, semiconductors known as metal halide perovskites are favored because they can be solution-processed into thin films with excellent photovoltaic efficiency.

A collaboration between KAUST and Oxford University researchers has now uncovered a strategy that grows perovskites into centimeter-scale, highly pure crystals thanks to the effect of surface tension.

In their natural state, perovskites have difficultly moving solar-generated electricity because they crystallize with randomly oriented grains. Osman Bakr from KAUST's Solar Center and coworkers are working on ways to dramatically speed up the flow of these charge carriers using inverse temperature crystallization (ITC).

This technique uses special organic liquids and thermal energy to force perovskites to solidify into structures resembling single crystals - the optimal arrangements for device purposes.

While ITC produces high-quality perovskites far faster than conventional chemical methods, the curious mechanisms that initiate crystallization in hot organic liquids are poorly understood.

Ayan Zhumekenov, a PhD student in Bakr's group, recalls spotting a key piece of evidence during efforts to adapt ITC toward large-scale manufacturing. "At some point, we realized that when crystals appeared, it was usually at the solution's surface," he says. "And this was particularly true when we used concentrated solutions."

The KAUST team partnered with Oxford theoreticians to identify how interfaces influence perovskite growth in ITC. They propose that metal halides and solvent molecules initially cling together in tight complexes that begin to stretch and weaken at higher temperatures. With sufficient thermal energy, the complex breaks and perovskites begin to crystallize.

But interestingly, the researchers found that complexes located at the solution surface can experience additional forces due to surface tension - the strong cohesive forces that enable certain insects to stride over lakes and ponds. The extra pull provided by the surface makes it much easier to separate the solvent-perovskite complexes and nucleate crystals that float on top of the liquid.

Exploiting this knowledge helped the team produce centimeter-sized, ultrathin single crystals and prototype a photodetector with characteristics comparable to state-of-the-art devices.

Although the single crystals are currently fragile and difficult to handle due to their microscale thicknesses, Zhumekenov explains that this method could help direct the perovskite growth onto specific substrates.

"Taking into account the roles of interfaces and surface tension could have a fundamental impact," he says, "we can get large-area growth, and it's not limited to specific metal cations - you could have a library of materials with perovskite structures."

Research paper

Tweet

Flisom launches next-gen flexible solar panels
Zurich, Switzerland (SPX) Sep 25, 2017
Flisom AG, an innovative and specialized solar technology company, backed by Tata Industries, a group of Swiss investors and the Swiss Federal Laboratories for Materials Science and Technology (Empa), reports that they were open for global orders at an exclusive roll out event for customers and partners in Zurich, Switzerland. Flisom showcased a range of applications including buildings-integrat ... read more

Related Links
King Abdullah University of Science and Technology
All About Solar Energy at SolarDaily.com

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only