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Camera-based characterization techniques for renewable energy technologies

Principal Investigator(s): 


One of the key issues in the field of photovoltaics (PVs) is how to achieve high optical to electrical power conversion efficiencies, not just for a few small (less than a cm-square) area laboratory devices, but in a manufacturing environment for production PV cells over very large areas, on the order of 100s of cm.  There are many factors that can affect the photovoltaic (PV) cell efficiency from theoretical maximums, including material defects that affect the lifetime of the photogenerated electron so they recombine before exiting the cell and areas of increased extraneous series resistance that prevent the voltage (electrical power) from being delivered to the load you wish to power. However, most current characterization techniques provide material information locally, on the order of 10s of nm, or conversely, the PV measurement represents a single average macroscopic number of the entire device. In fact, what you want is a 2D image of how various parameters that affect the PV cell efficiency are varying as a function of position across the entire device. One way of achieving this is by recording the luminescence given off by a PV cell under optical or electrical excitation (see Figure 1). 

I have, using unique camera equipment, imaged the electroluminescence for a copper-indium-gallium-diselenide (CIGS) photovoltaic cell and am working on algorithms to extract 2D images of the cell parameters like the minority carrier lifetime, series resistance, external quantum efficiency, and dark current just to name a few examples. Furthermore, such imaging technology promises to be extremely rapid, taking only a few seconds, instead of hours. When this program is successful, it promises to impact photovoltaic research and manufacturing by providing feedback information thereby dramatically improving efficiency yields, hopefully making photovoltaic technology even more cost competitive with coal. The techniques developed here can also potentially be used to monitor PV lifetime issues of cells in the field. The imaging technology can also be applied to LEDs and potentially fuel cells in a very analogous manner.
Figure 1: Image of electroluminescence emitting from a small CIGS solar cell with a characteristic 3-pronged metal grid pattern.