Higher Efficiency For Imec’s nPERT & Tandem CIGS Cell

• Imec made two announcements during the EU PVSEC 2018 regarding higher conversion efficiencies achieved for nPERT cells and perovskite/CIGS tandem cell
• For nPERT cells, it achieved 23.03% conversion efficiency using an industry compatible screen-printing process designed as an upgrade of conventional pPERC technology
• Another achievement was 24.6% efficiency for perovskite/CIGS tandem cell that Imec says paves the way for flexible solar cells and high-efficiency building-integrated PV (BIPV) applications

Belgium based research and innovation institute Imec has achieved a conversion efficiency of 23.03% on the latest generation of large-area monofacial screen-printed rear-emitter nPERT cells. It announced the feat at the EU PVSEC 2018 conference end of September. The cell has been certified by Germany's Fraunhofer ISE CalLab.

Made using an industry compatible screen-printing process designed as an upgrade of conventional p-PERC or p-type Passivated Emitted and Rear Cell processes, Imec's record cells is based on nPERT or n-type Passivated Emitter and Rear Totally diffused solar cell technology.

Imec is presenting its n-type PERT technology as a 'cost-effective contender' to n-type PERC solar cells. It fabricated the M2 sized cells on an area of 244.3 cm2 on its pilot line with industry compatible tools and recipes for which Imec says it used a layout of an n+region on the illuminated side and a p+region on the opposite side. It then added a cost-effective boron diffusion.

"Until now, nPERT solar technology has not yet found the traction it deserves in the industry," said Loic Tous, senior researcher at Imec. "With these ever-improving results, which we achieved by applying knowledge gained from our bifacial nPERT project, we are now demonstrating the potential of nPERT technology. The advantages in stability and efficiency potential over p-type PERC cells, while using the same equipment with the addition of a Boron diffusion, make this a very promising technology for future manufacturing lines."

According to Imec, its nPERT technology is projected to reach 23.5% efficiency by the end of 2018, and there is a clear technology roadmap to eventually surpass 24%.

24.6% perovskite/CIGS tandem cell efficiency

At the same event, Imec announced one more achievement – a 24.6% efficiency for perovskite/CIGS tandem cell that paves the way for flexible solar cells and high-efficiency building-integrated PV (BIPV) applications. It produced this thin-film tandem cell in partnership with EnergyVille and Solliance; the bottom CIGS cell comes from the Centre for Solar Energy and Hydrogen Research (ZSW).

This 4-terminal tandem comprised a perovskite solar cell stacked on top of a CIGS cell. To achieve the efficiency level, optical coupling layers were added to the tandem stack and transparent electrodes optimized to improve transmittance of the perovskite cell for near-IR light. The perovskite itself was optimized in terms of a wide bandgap of 1.72eV for higher tandem efficiency, shared Imec.

In July 2018, Imec achieved a 27.1% power conversion efficiency for 4-Terminal perovskite/silicon tandem PV cell (see 27.1% Perovskite/Si tandem Cell From IMEC).