Pressure Dependence of Photovoltaic Parameters in Thin Film Cu(In,Ga)Se2 Solar Cells

Abstract

We reported recently a strong reversible pressure dependence of photovoltaic (PV) parameters in thin film CdTe-based solar cells. The origin of this dependence is attributable to a window layer of CdS: the change in PV parameters is consistent with the values of its piezoelectric constants. This effect can be important for Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> technology, also using CdS as buffer layer, since the latter can be under considerable internal pressure resulting from highly nonequilibrium nature of thin-film PV deposition and lattice constants mismatch. In particular, the piezo-effect will translate the internal pressure into electric dipole charge distribution across the CdS layer and generate the electric potential difference having significant effect on PV parameters. We compare our observations of pressure dependent PV parameters in Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> devices with the previously reported data for CdTe-based PV. Several important features originate from the differences in CdS layer thickness, partial shading of CIGS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cell due to its substrate configuration, and possible shunting effects