Effects of Cu elements on Cu(In,Ga)Se2 film and solar cell

Abstract

The Cu elements of Cu (In, Ga) Se2 (CIGS) have very important influences on the electrical properties of CIGS absorber and solar cells. In this paper, Cu-poor and Cu-rich absorber layers (0.7 Cu/(Ga+In) (1.15) and solar cells are prepared by evaporation method. The SEM and Hall measurements reveal that Cu-rich material shows superior structural (larger grain size, better crystalline) and electrical (lower resistivity, higher mobility) properties to Cu-poor material. However, I-V tests show that the efficiency of Cu-poor solar cell is better than that of the Cu-rich device. The temperature-dependent I-V tests indicate that electron loss is mainly due to the bulk recombination in Cu-poor solar cell, and the activation energy of recombination is comparable to the band gap energy of Cu-poor solar cell. In contrast, in the Cu-rich devices the recombination at the heterointerface is dominant, and the activation energy is smaller than the band gap energy of the absorber material, which is an important drawback of open circuit voltage. Finally, Cu-poor surface on Cu-rich absorber is prepared by three-stage evaporation process, which reduces the short-circuit current and open-circuit voltage loss and optimizes the performance of CIGS solar cells. The efficiency of CIGS solar cell is achieved to be as high as more than 15%.