Many paths are pursued to continuously improve the efficiency of photovoltaic solar cells and their environmental footprint.
Among these, the use of a passivated poly-silicon-on-oxide contact on both sides of a silicon substrate is a promising way of achieving high conversion efficiencies with single or multi-junction photovoltaic cells.
The CEA at INES is developing an approach known as "High Temperature Heterojunction" and has named it CARLAH: this architecture combines ultra-thin poly-Si layers, of a thickness ≤ 20 nm, with films of Transparent Conductive Oxide (TCO). Our teams have designed a simplified processing method that generates strong "external getter" effects (extraction of metallic impurities) suitable for low-cost crystalline silicon (c-Si) substrates with a low carbon footprint. The structures created are, moreover, compatible with integration in Perovskites/c-Si tandem cells.
However, the tin doped indium oxide (ITO), most commonly used today for the manufacture of photovoltaic cells with passivated contacts, presents limitations related to the available indium resources and its cost. The solar community is therefore looking for alternatives to these materials.
In order to improve the economical balance and environmental footprint of this type of cell, the ITO layers usually used on the front panel have been compared by our laboratories with Zinc (AZO) based layers on single junction structures. Like ITO, the AZO layers studied here are deposited by PVD, a process that facilitates their transfer to industry.
The CEA at INES has just obtained with its CARLAH architecture a record cell with an efficiency of 22.4% in industrial format (M2) on monocrystalline substrates. A world record for this type of cell, on an industrial scale, as far as we know.
This result is very promising on the way to high efficiency cells with passivated contacts free of Indium.
The results obtained on the CARLAH technology are fruit of a collaboration with the company IBS, of the ANR OXYGEN project and of a thesis co-financed by ADEME.