IMEC has claimed a breakthrough in crystalline Si solar cell efficiencies that have reached an efficiency of 17.4 percent with the potential to scale to efficiencies above 20 percent with a decrease in cell thicknesses, according to the R&D centre based in Leuven, Belgium. 

The breakthrough comes from several years of research into a new cell concept dubbed ‘i-PERC’ (Passivated Emitter and Rear Cell). The PERC technology was not previously applicable to volume production solar cell applications; however the ‘i’ addition denotes ‘industrial’ use.

According to IMEC, the new process uses very thin silicon layers (<180µm) in which the classical Al back surface field, covering the whole rear of the Si solar cell, is replaced by local Al-alloyed contacts. In this process the rear is passivated by a dielectric stack, in which the contact openings are realized by laser ablation. Subsequently, an Al contact layer is evaporated which is fired in a belt-line furnace to create local back-surface fields.

IMEC also developed small-area crystalline Si solar cells with evaporated contacts. Lab-scale silicon solar cells have been realized, where for the first time the i-PERC process has been used as a method to passivate the rear side and to create local contacts. At the front side random pyramids are used in combination with a standard silicon nitride layer to provide good optical properties and surface passivation.

The evaporated Ti/Pd/Ag front contact grid is patterned by standard lithography. First attempts immediately resulted in an efficiency of 19% with an impressive short-circuit current of more than 39mA/cm², IMEC said.