Ga content and thickness inhomogeneity effects on Cu(In, Ga)Se2 solar modules

The fluctuation of Ga content and absorption layer thickness of Cu(In, Ga)Se2 (CIGS) solar modules is investigated by 3-dimensional numerical simulation. The band gap of CIGS is increased by the increasing Ga content, and the residual compressive strain. Strain effect worsens the degradation of the power conversion efficiency of CIGS module in addition to Ga fluctuation. The intracell Ga fluctuation degrades the open circuit voltage due to the minimum open circuit voltage in the parallel configuration, and also affects the short circuit current due to the Ga-dependent light absorption. The intercell Ga fluctuation leads to a more significant degradation for CIGS solar module efficiency than the intracell Ga fluctuation due to the additional degradation of the fill factor. The thickness fluctuation has a small effect on open circuit voltage, but causes strong degradation of short circuit current and fill factor, which leads to a more significant degradation on power conversion efficiency than Ga fluctuation to the same fluctuation percentage. In reality, the thickness can be tightly controlled within the fluctuation of 5% or less.