Progress and challenges with CdTe cell efficiency

CdTe solar-cell efficiency at Colorado State has now been independently verified above 18% on commercial glass. The parameters for the highest-efficiency cell are 863 mV for V
_OC
, 26.8 mA/cm
²
for J
_SC
, and 79.2% for fill-factor, combining for 18.3% efficiency. The cell features that allowed the increases include higher-temperature pre-heating before CdTe deposition, a Te layer to facilitate the back contact, MgZnO for the buffer layer, and an anti-reflective coating. The current and fill-factor have achieved large fractions of their ideal values for the CdTe band gap, but as is typical for CdTe cells, the voltage has not. Two general strategies to address the voltage deficit are described. One of these, electron reflection with fully-depleted CdTe, has achieved voltage increases of 60 mV with 1-μm CdTe and higher with sub-micron absorbers.