EPFL achieves 19.6% perovskite efficiency using vacuum coating

While there remains some skepticism as to the viability of perovskites in PV applications, a team from the EPFL has successfully deployed the vacuum-flash solution processing (VASP) method to achieve a 19.6% efficient cell. The EPFL team has made a number of breakthroughs on perovskite PV technology, including in tandem applications.

The EPFL researchers report that this results in a more uniform perovskite cell, with fewer impurities. An additional advantage of the VASP approach over spin-coating is that toxic chlorobenzene is not required to stimulate the growth of the perovskite crystal.

"It’s embarrassingly simple," said renowned PV researcher Michael Grätzel, who lead the EPFL team. "The shortcut we have found is to apply this mild [vacuum], just for a few seconds, and that does away with the anti-solvent." Grätzel made the comments when speaking with the Chemistry World publication.

"It [the VASP process] offers a method to get to high-quality electronic grade perovskite at low temperature – you never go above 100°C – and a very mild vacuum," Grätzel told Chemistry World.

The resulting perovskite film has been described as being "smooth" and "completely cover[ing] the substrate."

Importantly, the stability of the perovskite cell has been improved through the VASP method. The EPFL researchers report the cell remained stable when exposed to air for up to 39 days.

The EPFL cells were independently tested by Newport in the U.S.

At the opening of the recent SNEC conference in Shanghai, the University of New South Wales’ Martin Green reported that the progress of perovskites for PV applications has not been as encouraging as first thought.