Loss Analysis of Monocrystalline CdTe Solar Cells with 20% Active-Area Efficiency

We report a monocrystalline CdTe/MgCdTe double-heterostructure solar cell with an a-Si:H hole contact and an ITO/SiO _x electrode stack. Similar designs have achieved high open-circuit voltages, but low short-circuit current densities and fill factors have limited the cell efficiencies. We investigate the origin of these losses, and, in addressing some of them, achieve a maximum total-area efficiency of 18.5% and active-area efficiency of 20.3% measured under AM1.5G illumination. Additional cells have been measured with open-circuit voltages of up to 1.11 V, while still maintaining respectable fill factors and no rollover. The lack of rollover, either before or after open circuit, confirms the potential of this approach to reach very high efficiencies. The optical losses within the device are quantified and analyzed across the spectrum to determine if there exists potential for increased current generation through a reduction in parasitic absorption. In addition, fitting the current-voltage characteristic reveals that the leading cause of the less-than-ideal fill factor is series resistance, which contributes a 7% absolute loss.