Dye Sensitised Solar Cells “DSSC” Explained
DSSC was invented by Michael Grätzel and Brian O'Regan at the École Polytechnique Fédérale de Lausanne (EPFL) in 1991 and is therefore also known as “Grätzel cells”. DSSCs are electrochemical devices comprising a light-absorbing molecule anchored onto semiconducting titanium dioxide (TiO2) nanoparticles, which make use of sunlight to generate electricity.
The major benefits of DSSC technology are
- The use of a non-vacuum based and simpler manufacturing processes
- Use of non-toxic and abundant materials
- Superior performance in low and diffuse light
- Very low capital expenditure required relative to other PV technologies
These potential benefits have attracted a huge amount of interest in DSSC globally. The academic community working in DSSC is primarily focussed on ‘efficiency inflation’ i.e. reaching the highest efficiency at AM1.5 conditions on tiny cells. This is being achieved through better materials and dyes and other constituents in the cell.
A tuneable solar cell
The indoor light spectrum is very different from that of outdoor. Indoor conditions, primarily fluorescent lighting but also incandescent and LED, have a significant portion of the spectrum in the 600 nm range and below.
DSSC has a very high response in the 400-800 nm range, this explains the high power output it has in the visible, indoor light spectrum. DSSC has a spectral response that completely overlaps and matches with the visible, ambient indoor light; and this is the key to producing efficient power output in the indoor operating environment. This is the unique advantage of DSSC over other types of PV.
The graph above illustrates the efficiency of light harvesting for different wavelengths of incident fluorescent light (which has a very similar spectrum to white LED light. There is a dramatic increase in sensitivity to visible light between 400 and 750 nanometres compared to a bare TiO2 film.
For indoor applications, the measure of PV performance is also different. The AM 1.5 efficiency measurement is not relevant as it does not apply to the indoor PV operating conditions. The indoor performance metric is the power density output (microWatts/cm2) of a cell or module at a particular luminance (“lux”) level. The industry standard benchmark that has been adopted is power density at 200 lux. Putting this in context, the typical office lux intensity is between 400-700 lux.
The materials and dyes of DSSC can be tuned to produce maximum power density under low indoor lighting conditions, and SolarPrint has developed propriety DSSC designs and structures for low light that give optimum performance and sufficient power density for powering wireless sensors under low light applications. In summary;
Significantly higher power output indoors over competing solar technologiesdue to its ability to harness diffuse light togetherwith its low level of angular dependency
The potential to be a highly cost competitive technology under high volume production due to
- The use of relatively inexpensive manufacturing methods and simplified equipment
- The use of inexpensive materials in its manufacturing process.
In the future both flexible (metal or plastic) and rigid cell constructions are possible.
In particular one of the most unique characteristics of DSSC’s materials and dyes are their ability to be tuned to enable optimisation under low lighting conditions.