High efficiency BIFAcial SOLar cells on n-type silicon substrate – BIFASOL

Our proposal tenders the PROGELEC call. This proposal aims at developing a manufacturing process of high efficiency solar cell using n-type monocrystalline silicon. The consortium involves:

- LCP (CEA-INES), committed in cristalline silicon photovoltaic devices R&D,
- IEMN (CNRS), committed in thin films elaboration and characterization
- InESS (CNRS), committed in innovative laser processing
- OMGroup, committed in chemical and electrochemical products and processes
- Institut Lavoisier (CNRS), committed in plated layer elaboration, characterization, and fundamental electrochemistry.

Photovoltaic solar cells fabricated on n-type Cz (Czochralski) silicon do not exhibit the light induced degradation responsible for the reduction of p-type silicon cells electrical performances. N-type material also offers lower sensitivity towards metallic impurities and consequently higher minority carrier lifetimes than p-type silicon. Developing and transfering manufacturing process involving this actual n-type silicon opens the door to solar devices providing higher (>20%) and also more stable efficiencies than those obtained in current industrial production lines. Innovating features considered in this project deal with doping, passivation and metallization steps.

The goal of this project is to overcome conversion efficiencies limits on one hand, and cost-related industrialization hurdles on the other. LCP is already able to process n-type solar cells exhibiting efficiencies beyond 19% on Cz 148.6cm² substrates. The first phase of the project will be committed to improve doping and passivation processing steps in order to overcome the 20%.

Conventionnal screen-printing metallization generates shadow losses resulting in short-cricuit current reduction. Open circuit voltage is also degraded due to high recombinating activity beneath metallic contacts. Replacing traditionnal screen-printing by more advanced metallization technique should enable to reduce process costs as well as to improve cell performances. In this project, advanced metallization involving copper electroplating on top of a seed layer of nickel is considered. This second phase aims at developing solar cells with efficiencies higher up to 22% on large area wafers, and looks forward to reduce the manufacturing process cost by reducing raw material (such as contacting metal) consumption.

The bifaciality contributes to the development of a low-cost high efficient cell technology. Depending on PV module manufacturing and PV system setup, it is possible with bifacial module to gain up to 30% power thorough the year, compared to conventionnal PV module technology. Moreover the cell structure considered here is of particular interest for the use of thinner wafers (down to 100µm thick) due to the important stress reduction associated to the metallization technique chosen.