Using EDMR to Characterize Deep Level Defects in Novel Solar Cells

We have studied deep level defects in a new solar cell technology which is designed to be affordable and easy to manufacture. Electrically detected magnetic resonance (EDMR) and near-zero-field magnetoresistance (NZFMR) allow for the detection of defects by measuring the change in recombination current as a magnetic field is swept across the device and subject to RF (~500 MHz) for low field and X-band microwaves (9-10 GHz) for high field electromagnetic waves. The devices in this study consisted of polycrystalline silicon grown on passivated n-type Czochralski grown Si wafer with p+ and n+ regions located on the bottom and top of the device, respectively. We studied two types of devices that were manufactured with different open circuit voltages.

We find that the dominant defect centers in both cases were silicon dangling bonds; however, at different voltages we observed different dependences of the zero-crossing [endif]-->-values with the orientation of the magnetic field. The magnetic field at which resonance is observed provides insight into the structure of the defect centers, and, in this case, may provide some information on the physical location of the defects. The results suggest that silicon dangling bonds in the polycrystalline region are dominant in the sample with lower V_OC, and Pb0 like centers in the sample with higher V_OC.