Hurdle cleared on road to printable, low-cost perovskite solar cells

Much more printable power could be on the way soon, thanks to a manufacturing breakthrough that allows for lower cost and higher efficiency perovskite solar cells to move forward. Researchers at the University of Toronto have developed a new chemical reaction that solves one of the key challenges holding back development of the relatively new class of cells.

"Perovskite solar cells can enable us to use techniques already established in the printing industry to produce solar cells at very low cost," explains professor Professor Ted Sargent. "Potentially, perovskites and silicon cells can be married to improve efficiency further, but only with advances in low-temperature processes."

He and colleagues at the University of Toronto believe they've provided that advance by creating a new process to form the electron-selective layer (ESL) of a solar cell, which acts as a bridge between sun-catching crystals and electrical circuits, making it a key component in actually generating electricity from solar rays. The new process allows for the low-temperature creation of an ESL, clearing a major hurdle for perovskite solar cell production.

"The most effective materials for making ESLs start as a powder and have to be baked at high temperatures, above 500 degrees Celsius (932 F)," says team leader Dr. Hairen Tan. "You can't put that on top of a sheet of flexible plastic or on a fully fabricated silicon cell — it will just melt."

By developing a new reaction that enables an ESL to be grown already on top of an electrode in a solution, the team was able to use a fraction of the heat to create the layer. Temperatures stay below 150 degrees Celsius (302 F) and below the melting point of many plastics.

This should allow for developers to better tap into the potential advantages of perovskite, which is based on raw materials that can be mixed with liquid and used in inkjet-type printers to literally print energy-gathering crystals onto glass, plastic or other materials. That's a big difference from the way traditional, silicon-based solar cells are produced, requiring lots of intensive processing with hazardous solvents and temperatures in excess of 1,000 degrees Celsius (1,832 F).

The Toronto team also claims they were able to boost efficiency by coating the particles that make up the ESL with chlorine atoms to better bind it to the perovskite crystal layer. They published a paper in the journal Science that reports an efficiency of 20.1 percent in solar cells made using the new method.

"This is the best ever reported for low-temperature processing techniques," says Tan, noting that cells made using high-temperature methods are only slightly more efficient, at 22.1 percent, and the best silicon cells only reach 26.3 percent.

One downside of perovskite cells is that they don't last nearly as long as their silicon competition, but the cells Tan's team developed retained 90 percent of their efficiency even after a respectable 500 hours of use.

But most important is the myriad new applications we could see for cheap and easy-to-produce solar cells by keeping perovskite production temperatures low. Tan envisions solar cells on smartphone covers or in window tinting or teaming up with traditional cells for even greater efficiency.

"With our low-temperature process, we could coat our perovskite cells directly on top of silicon without damaging the underlying material," says Tan. "If a hybrid perovskite-silicon cell can push the efficiency up to 30 percent or higher, it makes solar power a much better economic proposition."

Source: University of Toronto