Solar cells convert sunlight into electrical power and will contribute significantly to regenerative energy supply in the future. Thin-film solar cells made of crystalline silicon receive increasing interest in order to produce power at lower cost.
The team’s main focus of research includes

• Thin-film solar cells made of laser-crystallized silicon on glass
• Silicon nanowires for solar cells
• Laser modification of solar cells (laser doping, laser annealing)

In the field of photovoltaics, we are developing thin-film solar cells based on crystalline silicon films on glass. We have concentrated our efforts in cells consisting of multicrystalline silicon layers with crystallites  exceeding 0.1 mm in size as well as in nanowire solar cells. The aim of our work is to produce high-quality silicon material on inexpensive substrates, such as glass, using industrially relevant processes, thereby preparing highly-effective solar cells. In addition, we are developing laser processes to be used for the modification of solar cell materials. Both the solar cell materials and the solar cells themselves are characterized by various methods.

Multicrystalline Silicon Thin-film Solar Cells

Coarsely grained layers well suited for solar cells can be easily prepared on inexpensive glass substrates in a two-step process. In the first step, a seed layer is produced with the desired crystal structure consisting of grains over 0.1 mm in size on a glass substrate. This is performed by a laser crystallization process using high-power diode lasers. This process is a unique feature that sets us apart from the rest of the world. In a second step, the seed layer is epitaxially thickened to a solar cell approx. 2 µm thick. Here, we are investigating different methods, such as: laser-based processes and solid-phase epitaxy in the oven. Our aim is to optimize the quality of the crystal without driving up the production cost. One particularly noteworthy feature is depositing amorphous silicon starting layer by  electron beam evaporation . This method exhibits the highest silicon deposition rates and is thus much more effective than the more commonly used CVD process.

Nanowire Solar Cells

One completely new idea is to use silicon nanowires for solar cells. The nanowires are a few 10s of nm to a few 100 nm thick and are arranged like a carpet. These nanowire carpets absorb light much better than flat thin films and thus offer solar cells a significant advantage. The nanowires are produced by growing them from gas precursors or by etching them chemically from thin films. In both cases glass is used as a substrate on which a laser crystallized silicon layers is prepared. Solar cells are either produced directly from the nanowires or as hybrid cells from nanowires and polymers.

Laser Modification of Solar Cells

In addition to laser crystallization and structuring, laser processes are also interesting for doping silicon solar cells and for improving the crystal quality. For doping purposes, we are developing processes with short-pulse lasers. For the annealing of silicon we are evaluating the application of diode lasers.