South Korean researchers from Ulsan National Institute of Science and Technology (UNIST) have claimed to have achieved the world’s ‘highest’ power conversion efficiency (PCE) of 25.8% for a perovskite solar cell. The National Renewable Energy laboratory (NREL) of the US has certified the efficiency as 25.5%, which is also highest confirmed efficiency for such a perovskite single-junction cell.

The team achieved this level by forming an interlayer between a SnO2 electron-transporting layer and a halide perovskite light-absorbing layer to minimize interfacial defects that substantially lower power conversion efficiency of the devices. They did this by coupling CI-bonded SnO2 with a CI-containing perovskite precursor.

Why this interlayer works is because it can charge extraction and transport from the perovskite layer and has less interfacial defects, explained the team. They further add that ‘unencapsulated devices maintained about 90% of their initial efficiency even after continuous light exposure for 500 hours’.

According to the researchers, efforts hitherto made to reduce the interfacial defects have focused mainly on surface passivation. What’s been difficult to achieve is passivating the perovskite surface that interfaces with the electron transporting layer since surface-treatment agents may dissolve electron-transporting layer during coating the perovskite thin film.

“The existence of such a coherent interlayer allowed us to fabricate perovskite solar cells with a power conversion efficiency of 25.8% under standard illumination,” added the team that believes these findings provide ‘guidelines for designing defect-minimizing interfaces between metal halide perovskites and electron-transporting layers’.

The findings of the team have been published in the Nature journal with the title Perovskite solar cells with atomically coherent interlayers on SnO2 electrodes.

In February 2021, UNITS reported 18.04% efficiency for a hybrid tandem solar cell (see 18.04% Efficiency For Perovskite BHJ Tandem Solar Cell).