Researchers at the University of Toronto have developed a novel way to print perovskite solar cells easily and at a low cost. This breakthrough could lead to low-cost, printable perovskite solar panels capable of turning nearly any surface into a power generator.

Perovskite materials can be mixed into a liquid to form an ink, which allows them to be printed onto glass, plastic or other materials using a simple inkjet process. The common catch is, however, that in order to generate electricity, electrons excited by solar energy must be extracted from the crystals so they can flow through a circuit. That extraction happens in a special layer called the electron-selective layer, or ESL. The difficulty of manufacturing a good ESL has been one of the key challenges holding back the development of perovskite solar cell devices.

“The most effective materials for making ESLs start as a powder and have to be baked at high temperatures, above 500 degrees Celsius,” says the team. “You can’t put that on top of a sheet of flexible plastic or on a fully fabricated silicon cell — it will just melt”. In this work, the researchers developed a new chemical reaction that enables them to grow an ESL made of nanoparticles in solution, directly on top of the electrode. While heat is still required, the process always stays below 150 degrees C, much lower than the melting point of many plastics.

The new nanoparticles are coated with a layer of chlorine atoms, which helps them bind to the perovskite layer on top — this strong binding allows for efficient extraction of electrons. The team reports the efficiency of solar cells made using the new method at 20.1%.

Another advantage is stability. Many perovskite solar cells experience a severe drop in performance after only a few hours, but the newly fabricated cells retained more than 90% of their efficiency even after 500 hours of use.