Spectrally resolved photoluminescence studies on Cu(In,Ga)Se 2 solar cells with lateral submicron resolution

Abstract

We have analyzed thin film glass/Mo/Cu(In 1− x ,Ga x )Se 2/CdS/ZnO solar cells ( x = 0.3–0.5) and samples without the ZnO layer in a confocal scanning microscope setup with lateral submicron resolution and we have recorded a full photoluminescence (PL) spectrum for each pixel of the respective scans (20 μm × 20 μm). Our analyses show non-negligible spectral and intensity variations of the PL in length scales of a few micrometers. The recorded spectra (Y PL( x, ω)) are seemingly composed of three basic peaks (B PL, i ( ω); Y PL( x, ω) = a( x)·B PL,1( ω) + b( x)·B PL,2( ω) + c( x)·B PL,3( ω)). Hence we are able to extract values for the quantifiers a, b, c which exhibit a laterally non-random distribution, yielding qualitative and quantitative fluctuations of the material properties in the few micron scale as neighbouring grains or grain centres and boundaries. We discuss these variations in terms of locally fluctuating splitting of quasi-Fermi levels, of local variations of band gap and material composition, which similarly have commonly known impacts on the performance of CIGSe devices.