Recombination currents in microcrystalline silicon solar cells studied by electrically detected magnetic resonance

We report on a detailed study of electrically detected magnetic resonance (EDMR) of the dark current in microcrystalline silicon (μc-Si:H) and amorphous silicon (a-Si:H) pin solar cells. For small forward bias, in both types of cells the EDMR spectrum is dominated by a positive signal at g = 2.005. The signal is associated with the recombination current and is determined by recombination through neutral dangling bonds in the space charge region. Whereas the EDMR signal of the a-Si:H pin cells changes sign above a bias of 0.75 V indicating the reversal of the electric field in the i layer, the signal in the pc-Si:H diode disappears above 0.6 V. With the help of a simple model developed for c-Si pn junctions, we will show that the EDMR behavior of the μc-Si:H cell can be described by recombination and diffusion currents. This is different from what we find for a-Si:H pin devices, where an additional drift component is needed to fully describe the EDMR behavior.