Daniel Kray

Laser-doped silicon solar cells by Laser Chemical Processing (LCP) exceeding 20% efficiency

The introduction of selective emitters underneath the front contacts of solar cells can considerably increase the cell efficiency. Thus, cost-effective fabrication methods for this process step would help to reduce the cost per Wp of silicon solar cells. Laser Chemical Processing (LCP) is based on the waterjet-guided laser (LaserMicroJet®) developed and commercialized by Synova S.A., but uses a chemical jet. This technology is able to perform local diffusions at high speed and accuracy without the need of masking or any high-temperature step of the entire wafer. We present experimental investigations on simple device structures to choose optimal laser parameters for selective emitter formation. These parameters are used to fabricate high-efficiency oxide-passivated LFC solar cells that exceed 20% efficiency.

High-efficiency silicon solar cells for low-illumination applications

At Fraunhofer ISE the fabrication of high-efficiency solar cells was extended from a laboratory scale to a small pilot-line production. Primarily, the fabricated cells are used in small high-efficiency modules integrated in prototypes of solar-powered portable electronic devices such as cellular phones, handheld computers etc. Compared to other applications of high-efficiency cells such as solar cars and planes, the illumination densities found in these mainly indoor applications are significantly below 1 sun. Thus, special care was taken to keep the cell efficiency level high even at very low illumination levels. For this reason, particularly the cell border was analyzed and optimized carefully. The excellent cell characteristics achieved at low illumination densities increase the benefit of a solar power supply for such devices by an order of magnitude if compared to standard solar cells.

Analysis of Selective Phosphorous Laser Doping in High-Efficiency Solar Cells

This paper focuses on the analysis of local phosphorous laser doping in high-efficiency solar cells. Those so-called selective emitters are intended to reduce the contact recombination and resistance in order to increase the solar conversion efficiency. Sample solar cells are prepared using laser chemical processing as the laser doping technique and analyzed via analytical models and suns-V oc measurements at high illumination densities. It can be shown that fully ohmic contacts can be manufactured on the investigated selective emitters which exhibit low dark saturation currents. The specific recombination current density of the local laser doping is determined experimentally to be < 8.5 times 10-13 A/cm2 for planar surfaces.

ACE Designs: the beauty of rear contact solar cells

Presents an outline of the work done in the EC co-funded project ACE Designs. The objective of this project was to develop rear contact solar cell designs and to demonstrate their applicability as an alternative crystalline silicon technology for industrial module production. An overview of the results is given with links to the most relevant, publications for further details. The most important result of this project was that rear contact solar cells are a feasible, attractive and cost effective alternative to the well-known front contacted solar cell.