The role of gallium in CuInSe2 solar cells fabricated by a two-stage method

Incorporation of Ga in CuInSe₂ thin film solar cells formed by a two-stage method results in improved adhesion between the CuInSe₂ absorber layer and the Mo back electrode. The original intent of incorporating Ga was to increase the bandgap by forming a homogeneous CuIn_1-xGa_xSe₂ quaternary absorber. Rather than the expected increase in bandgap by uniform substitution of Ga for In, adhesion was improved by the formation of a Ga-rich interfacial layer between the absorber and the molybdenum. In addition to improved adhesion, an increase in efficiency due to improved open circuit voltage was observed. Structural models for the absorber layer are proposed based on Auger analysis and solar cell performance data