Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Novel processes

Several novel processes were investigated during the first part of the Topsicle project:
- Single-Step Selective Emitter
- Fine-Line Printing
- Angled Buried Contact (abc) Concept

Single-Step Selective Emitter:
University of Konstanz was working on a single step selective emitter cell using porous silicon as a diffusion barrier. Tests with short wavelength lasers were done to find optimal laser parameters necessary to remove the porous silicon (in the selected regions) prior to the diffusion. In a first experiment the cleaning step before the diffusion unfortunately removed the porous silicon. Further experiments have been carried out to optimise the porous silicon thickness and diffusion parameters to have optimal the sheet resistance in both the highly and lowly doped regions.
More research is needed (and will be carried out) before this novel process can be assessed for dissemination.

Fine-Line Printing:
With the aim of achieving both narrow and high fingers for low shadowing losses and high finger conductivity a method of fine-line printing was investigated. By printing and drying several times it was possible to achieve fingers of about 60 µm width and 60 µm height. Multiple prints in exactly the same position were demonstrated. Test wafers with up to 10 printed layers were made. Solar cells were made with 3x and 5x front side printing on both iso- and un -textured wafers. The cells show an approximately 0.5 mA/cm2 higher current compared to standard screen-printed cells. In the case of the un-textured cells, the increase in Jsc was accompanied by a decrease in fill factor (approximately 2-3% absolute). No decrease in fill factor was seen for the iso-textured cells. These results are promising, and can probably be used to disseminate outside the consortium.

Angled Buried Contact Concept:
The Angled Buried Contact cell design is a front metallisation scheme that results in negligible shading. The metal is deposited in angled grooves and is in the ideal case not visible by looking from a perpendicular view to the cell surface. The process does not require any additional process steps compared to a standard buried contact process, it is slightly simplified. The proof of concept was shown and an increase in short circuit current of 0,7mA/cm2 was demonstrated.

The LPCVD (low pressure) silicon nitride has to be replaced by PECVD (plasma enhanced) silicon nitride because a directional deposition is neccesary. Depostion pressure of PECVD system must be adjusted to reach low pinhole density in the silicon nitride layer. Overplating (and thus higher shading losses) because of silicon nitride pinholes and local shunting were the main problems of first cell runs.

Reported by

PO Box X916
78457 Konstanz