Technology Offers Solar Technology / Photovoltaics

Highly conductive pastes for printable electronic applications and devices

At the Karlsruhe Institute of Technology (KIT), a new platform concept for the formulation of highly conductive, printable pastes has been developed. Corresponding pastes are free of polymeric or other non-volatile stabilizers and rheology control agents. Nevertheless, rheological properties like low-shear viscosity and yield stress can be adjusted in a wide range. Thus sedimentation /aggregation is prohibited and long-term stability can be guaranteed even for suspensions of high density particles (e.g. Ag, Ni). Also full control of the application behavior in many different printing/coating operations is furnished.



Simultaneous production of differently doped areas on a solar cell using borosilicate glass

When producing rear contact solar cells, both negatively and positively doped areas need to be produced on the rear of the solar cell. Moreover, the front side of the solar cell has to be sufficiently passivated in order to minimize surface recombination. This means three differently doped areas are required.
Scientists of the University of Konstanz have now developed a new method for producing these three areas in a single diffusion step. This approach is based on the application of a borosilicate glass layer and partial silicon nitride masking on the rear of the solar cell.



Optimum passivation of defects in crystalline silicon solar cells

Monocrystalline solar cells that are produced using the relatively inexpensive CZ method (Czochralski method) display a noticeable drop in efficiency of more than 1% in absolute figures under sunlight within a few hours. This effect is called Light Induced Degradation (LID). Solar cells and modules are sold in relation to their performance. This is why elimination of light induced degradation holds tremendous economic potential. As early as 2006, a simple method for the regeneration of solar cells was developed at the University of Konstanz which proved to be very efficient at moderate temperatures and light intensity.
This well-known method has now been significantly enhanced and modified: the degradation of the Cz silicon solar cells can now be largely eliminated during the production process. The regeneration process is now carried out at much higher temperatures than before, using hydrogen that had diffused into silicon nitride. This makes the regeneration process a lot more efficient and faster. Ideally, this step follows the co-firing process during the production.



Non-permanent contacting for the characterization and classification of busbarless solar cells

Scientists at the University of Konstanz have developed a measuring device for non-permanent contacting of busbarless solar cells that allows for precise and direct characterization of electrical properties. As each contact finger can be contacted repeatedly over reversibly releasable connections the device allows for accurate measurement of I-V characteristics without requiring subsequent adjustment with correction factors.



Regeneration of boron-oxygen defects in monocrystalline solar cells made of Cz silicon

The efficiency of solar cells made of CZ silicon decreases by more than 1% in absolute figures under sunlight within a few hours (light induced degradation - LID). At the University of Konstanz a method was developed that makes it possible to stabilize the efficiency of the solar cell at nearly its output level. During production the solar cells are regenerated by either illumination at temperatures of between 100 and 230 degrees or applying voltage. The method can be easily integrated in the conventional manufacturing process and allows for an increase in efficiency by up to 5% rel.



Wet chemical process for back side smoothing of industrially manufactured solar cells

The efficiency of solar cells can be increased simply and effectively by smoothing the back side through wet chemical etching. A smooth surface structure makes the back side highly reflective. During smoothing, the parasitic emitter on the back side is etched away as well, while a viscous paste protects the microscopic pyramidal structure on the front side. The process utilizes solely inexpensive and established technologies in industrial manufacturing of solar cells.



Silver-free, nickel-containing paste for establishing contacts in solar cells

Subject of this innovation is a silver-free paste for establishing contacts in solar cells with nickel, nickel compounds or titanium instead of silver.
The process involves the local opening of the dielectric layer at moderate temperatures, thereby allowing the nickel particles in the paste to form nickel silicide with the surface of the silicon substrate. The high-energy-step of firing the silver contacts with glass frit can be dispensed with.
Furthermore, it is possible to strengthen the nickel layer with copper or tin to increase the electrical conductivity of the contacts still further.