Imec presents an improved
processing technique for germanium-based thermophotovoltaic (TPV) cells resulting
in significant reduction of cell cost, an essential step to develop a market
for thermophotovoltaic applications. Imec's newly developed TPV cells
are fabricated on germanium substrates with an optimized surface, specifically
designed and manufactured for this application.
Thermophotovoltaic cells convert radiation from heat sources with a temperature
lower than the sun's temperature. TPV cells are ideally suited to be used
in an industrial context, for example to generate electricity from waste heat
released during steel or glass production. Alternatively, TPV cells can be added
to domestic heating systems to co-generate electricity besides hot water. TPV
cells may therefore reduce the waste and hence increase the efficiency of domestic
heating systems.
However, due to the overall complexity of a full TPV system and the relatively
high cost of existing suitable cells, TPV systems are yet to find entrance to
industrial and consumer applications. Imec's newly developed fabrication
process is an important first step in opening up the market potential for this
very promising technology.
The emission peak of selective emitters typically used in TPV systems is close
to the bandgap of germanium. Therefore, germanium photovoltaic devices are well
suited as receivers for this type of systems. Germanium-based TPV cells were
up to now fabricated on epi-ready substrates marketed for the epitaxial growth
of III-V layers. However, Imec's processing method does not involve any
epitaxial deposition steps, as the emitter is formed by diffusion and passivation
obtained by using amorphous Si. During a research program, specifically designed
Ge substrates for this application were manufactured and tested. Spectral response
measurements comparing the traditional TPV cells starting from epi-ready substrates
with TPV cells defined on specifically engineered Ge substrates show that the
latter have a remarkably better quantum efficiency. This directly translates
into a higher waste heat to electricity conversion efficiency.
Jef Poortmans, Director Photovoltaics at imec: “Imec's research
into photovoltaics aims at finding techniques to fabricate cost efficient and
more efficient solar cells. We have built up a strong expertise in silicon solar
cells of more than 25 years. We successfully used this knowledge for our TPV
research. We applied imec's proprietary surface passivation techniques,
novel contacting technologies and material knowledge to improve the quantum
efficiency of our TPV cells, resulting in higher cell performance and cost reduction.”
Posted June 8th, 2010