Fixing perovskite solar cell defects with potassium

Scientists led by Cambridge University have discovered that adding a simple solution of potassium to the ink solution has the effect of ‘healing’ defects in metal-halide perovskite films, and immobilizing ion movement. This, according to the researchers, could push the material to higher efficiencies, while also increasing its stability.

March 23, 2018 Mark Hutchins

Image: Cambridge University/Matt Klug

Perovksite solar cells are well known among researchers for their potential to act as cheap to produce, highly efficient solar cells. Universities and institutes the world over are working on solutions to the stability and sensitivity issues that have so far prevented their commercial uptake.

A team led by the University of Cambridge has achieved a breakthrough, discovering that simply adding a potassium iodide solution to the perovskite ink can have the dual effects of healing defects that limit the material’s efficiency, and immobilizing ion movement, which increases stability.

“So far, we haven’t been able to make these materials stable with the bandgap we need, so we’ve been trying to immobilize the ion movement by tweaking the chemical composition of the perovskite layers,” said Dr Sam Stranks from Cambridge’s Cavendish Laboratory, who led the research. “This would enable perovskites to be used as versatile solar cells or as colored LEDs, which are essentially solar cells run in reverse.”

The technique developed by the researchers, described in the journal Nature, involves adding potassium iodide to the perovskite solution. The scientists that their technique is compatible with roll-to-roll processes, and therefore easily scalable.

“We’ve found that perovskites are very tolerant to additives – you can add new components and they’ll perform better,” said first author Mojtaba Abdi-Jalebi, a PhD candidate at the Cavendish Laboratory. “Unlike other photovoltaic technologies, we don’t need to add an additional layer to improve performance, the additive is simply mixed in with the perovskite ink.”

Devices made using the perovskite & potassium solution achieved 21.5% efficiency, and ‘showed good stability’ according to the researchers. The team theorizes that their cells could be used as the top layer in a tandem solar cell, with either crystalline silicon or an alternative cell material underneath.

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