Paul van Gerven
18 February

Amolf researchers have demonstrated that perovskites can, in fact, exist as amorphous materials. This discovery could significantly increase the efficiency of perovskite solar cells.

Perovskite solar cells are typically made from lead and organic cations and halide (bromide or iodide) anions. These materials are highly crystalline by nature, which is a good thing for solar cells because crystallinity increases efficiency. The amorphous state can be helpful too, however. The very best silicon solar cells feature an amorphous layer, which helps getting electrons out. This should work for perovskite solar cells as well.

Crystalline perovskites (green) grow when relatively little acetate precursor is present. As the amount increases, more amorphous material (light blue) appears. Credit: Amolf

Erik Garnett, Susan Rigter and colleagues of Amolf found that the quantity of one of the organic cations, ie methylammonium acetate, during perovskite synthesis influences the crystallinity of the resulting material. The more acetate precursor, the more amorphous it is. This turned out to be a widely applicable principle: it also works with other organic cations and halides.

Spectroscopic measurements suggest that amorphous perovskite has indeed the desired characteristics to increase solar cell efficiency. The next step in the research is producing this type of solar cell, stacking a layer of crystalline perovskite with a layer of amorphous perovskite. That’s more difficult than producing just amorphous perovskite because the underlying crystalline layer provides an ordered template, making it easier for atoms to pack in an ordered fashion.