In theory, silicon-based solar cells are capable of converting up to 30 percent of sunlight to electricity — although, in reality, the different kinds of loss mechanisms ensure that even under ideal lab conditions it does not exceed 25 %. Advanced heterojunction cells shall affront this problem: On top of the wafer’s surface, at temperatures below 200 °C, a layer of 10 nanometer disordered (amorphous) silicon is deposited. This thin film is managing to saturate to a large extent the interface defects and to conduct charge carriers out of the cell. Heterojunction solar cells have already high efficiency factors up to 24,7 % — even in industrial scale. However, scientists had until now only a rough understanding of the processes at the remaining interface defects.
Now, physicists at HZB’s Institute for Silicon Photovoltaics have figured out a rather clever way for detecting the remaining defects and characterizing their electronic structure. “If electrons get deposited on these defects, we are able to use their spin, that is, their small magnetic moment, as a probe to study them,” Dr. Alexander Schnegg explains. With the help of EDMR, electrically detected magnetic resonance, an ultrasensitive method of measurement, they were able to determine the local defects’ structure by detecting their magnetic fingerprint in the photo current of the solar cell under a magnetic field and microwave radiation.
source : http://www.sciencedaily.com/releases/2013/03/130327104151.htm