Potassium offers perovskite-based solar cells an efficiency boost

A simple potassium solution could boost the efficiency of next-generation solar cells, by enabling them to convert more sunlight into electricity.

Atomic scale view of perovskite crystal formation Credit: Matt Klug
Atomic scale view of perovskite crystal formation Credit: Matt Klug

Scientists at the University of Cambridge have recently discovered that a simple potassium solution could boost the efficiency of next-generation solar cells. It could heal the defects and immobilized ion movement, which to date have limited the efficiency of cheap perovskite solar cells.

According to scientists, such perovskite-based solar cells could potentially be used for an efficiency-boosting layer on top of existing silicon-based solar cells, or be made into stand-alone solar cells or colored LEDs.

The solar cells in the examination depend on metal halide perovskites – a promising gathering of ionic semiconductor materials that in only a couple of short a long time of improvement now equal business thin film photovoltaic advancements as far as their proficiency in changing over daylight into power. Perovskites are modest and simple to create at low temperatures, which makes them appealing for cutting-edge solar cells and lighting.

Dr. Sam Stranks from Cambridge’s Cavendish Laboratory, who led the research said, “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. This would enable perovskites to be used as versatile solar cells or as colored LEDs, which are essentially solar cells run in reverse.”

Notwithstanding the capability of perovskites, a few restrictions have hampered their proficiency and consistency. Small deformities in the crystalline structure of perovskites, called traps, can make electrons get ‘stuck’ before their vitality can be saddled. The simpler that electrons can move around in a solar cell material, the more proficient that material will be at changing over photons, particles of light, into power. Another issue is that particles can move around in the solar cell when enlightened, which can cause an adjustment in the bandgap – the shade of light the material ingests.

In the investigation, the specialists changed the synthetic piece of the perovskite layers by adding potassium iodide to perovskite inks, which then self-amass into thin movies. The strategy is good with move to-move forms, which implies it is versatile and economical. The potassium iodide framed an ‘decorative’ layer over the perovskite which had the impact of ‘mending’ the traps with the goal that the electrons could move all the more unreservedly, and also immobilizing the particle development, which makes the material more steady at the coveted bandgap.

The specialists exhibited promising execution with the perovskite bandgaps perfect for layering over a silicon solar cell or with another perovskite layer – alleged pair solar cells. Silicon coupled solar cells are the in all probability first boundless utilization of perovskites. By including a perovskite layer, light can be all the more proficiently collected from a more extensive scope of the solar range.

Stranks said, “Potassium stabilizes the perovskite bandgaps we want for tandem solar cells and makes them more luminescent, which means more efficient solar cells. It almost entirely manages the ions and defects in perovskites.”

“The perovskite and potassium devices showed good stability in tests and were 21.5% efficient at converting light into electricity, which is similar to the best perovskite-based solar cells and not far below the practical efficiency limit of silicon-based solar cells, which is (29%). Tandem cells made of two perovskite layers with ideal bandgaps have a theoretical efficiency limit of 45% and a practical limit of 35% – both of which are higher than the current practical efficiency limits for silicon. You get more power for your money.”

First author Mojtaba Abdi-Jalebi, said, “We’ve found that perovskites are very tolerant to additives – you can add new components and they’ll perform better. 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.”

Reference:
Mojtaba Abdi-Jalebi et al. ‘Maximising and Stabilising Luminescence from Halide Perovskites with Potassium Passivation.’ Nature (2018). DOI: 10.1038/nature25989