Stability of perovskite solar cells reaches next milestone

• Perovskite semiconductors promise highly efficient and affordable solar cells. Nonetheless, the semi-organic product is very sensitive to temperature differences, which can swiftly cause fatigue damages in typical outdoor usage. Adding a dipolar polymer compound to the precursor perovskite solution assists to neutralize this.

This has now been shown in a research published in the journal Science by an international group led by Antonio Abate, HZB. The solar cells generated in this way attain efficiencies of well above 24 %, which hardly go down under fast temperature level fluctuations between -60 as well as +80 Celsius over one hundred cycles. That corresponds to about one year of outdoor usage.

The product class of halide perovskites is seen as an excellent hope for much more solar energy at even reduced prices. The products are very inexpensive, can be refined into thin films with minimal power input and accomplish efficiencies that are considerably more than those of standard silicon solar cells.

The objective: 20 years outdoor stability

Nevertheless, solar modules are anticipated to provide secure result for a minimum of 20 years in outdoor problems while exposed to large temperature level fluctuations. Silicon PV manages this quickly, whereas the semi-organic perovskites lose performance instead quickly.

" Sunlight can heat up the inside of a PV cell to 80 Celsius; at night, the cell then cools down promptly to the outside temperature level. This triggers large mechanical stresses in the thin layer of perovskite microcrystals, creating issues as well as also neighborhood phase transitions, to make sure that the thin film loses its quality," explains Prof. Antonio Abate, who heads a huge team at HZB.

Together with his team and a variety of worldwide partners, he has checked out a chemical variant that substantially improves the stability of the perovskite thin film in different solar cell architectures, among them the p-i-n architecture, which normally is a little much less efficient than the more frequently utilized n-i-p architecture.

A 'soft shell' against stress

" We maximized the tool framework and also procedure specifications, building on previous results, and also ultimately can achieve a definitive improvement with b-poly( 1,1-difluoroethylene) or b-pV2F for short," states Guixiang Li, who is doing his Ph.D. managed by Prof. Abate. b-pV2F molecules appear like a zigzag chain inhabited by rotating dipoles.

" This polymer seems to twist around the specific perovskite microcrystals in the thin film like a soft shell, creating a sort of cushion against thermomechanical stress," Abate explains.

Record efficiency for p-i-n architecture: 24.6%.

As a matter of fact, scanning electron microscope photos show that in the cells with b-pV2F, the tiny granules nestle a little closer. "Furthermore, the dipole chain of b-pV2F improves the transportation of charge carriers and thus boosts the efficiency of the cell," claims Abate. Without a doubt they produced cells on a laboratory scale with efficiencies of up to 24.6%, which is a record for the p-i-n architecture.

The newly produced solar cells were subjected over a hundred cycles in between +80 Celsius and also -60 Celsius as well as 1000 hours of constant 1-sun equivalent illumination. That corresponds to about one year of outdoor use.

" Even under these extreme stresses, they still accomplished 96 % efficiency in the end," Abate stresses. That is currently in the appropriate order of magnitude. If it is currently viable to reduce the losses a little further, perovskite solar modules can still produce a lot of their original outcome after 20 years-- this goal is now coming within reach.