Efficiency Of CIGS Solar Cells Research Articles

Band-gap engineering in CIGS solar cells using Nelder–Mead simplex optimization algorithm

Band-gap grading in a CIGS absorber and a conduction band offset at n/p hetero-interface are two important parameters of band-gap engineering aiming at high efficient CIGS solar cells. To obtain optimal CIGS absorber's band-gap grading profile an automatic optimization loop based on Nelder–Mead simplex optimization algorithm has been implemented. The optimization problem is described with an objective function, which—by varying the input parameters—is minimized or maximized. In our study two types of objective functions are used; optical and electrical. As the most optimal profile a parabolic, double graded band-gap profile with a positive or nearly zero conduction band offset at n/p hetero-interface is calculated. Structures with different CIGS absorber thicknesses and bulk and/or hetero-interface recombination lifetimes are examined and their optimized parameters are discussed in the light of experimental achievements.

Characterization of the Cu(In,Ga)Se 2/Mo interface in CIGS solar cells

In a high efficiency CIGS solar cell, we observed a MoSe 2 layer at the interface by SIMS, TEM and X-ray diffraction. MoSe 2 had a layer structure and the layers were oriented perpendicular to the Mo layer. The MoSe 2 contributes to the improvement of adhesion at the CIGS/Mo interface. The effects of the MoSe 2 layer on the electrical and photovoltaic properties of CIGS solar cells were investigated. The CIGS/Mo heterocontact, including the MoSe 2 layer, is not Schottky-type, but a favorable ohmic-type by the evaluation of dark I– V measurement at low temperature. A characteristic peak at 870 nm is observed in the differential quantum efficiency of a solar cell with a CIGS thickness of 500 nm. This peak relates to the absorption of the MoSe 2 layer. The band gap of MoSe 2 is calculated to be 1.41 eV from the absorption peak.