Influence of the selenium/metal flux ratio on the crystallinity of widegap Cu(In/sub 0.4/Ga/sub 0.6/)Se/sub 2/ thin films and devices

The influence of the Se/metal flux ratio on the crystallinity of widegap Cu(In/sub 0.4/Ga/sub 0.6/)Se/sub 2/ thin films with bandgap energy of 1.4 eV as well as the device performance has been investigated. The Se/metal flux ratio during the 1st stage of the modified three-stage process was varied from 10 to 118. As the Se/metal flux ratio was increased to 51, large crystal grains of CIGS thin films were observed to grow and the cell efficiency improved. Moreover, the (204)/( 112) peak X-ray intensity ratio increased, whereas, almost no change in the RHEED pattern was observed. These results suggest that the bulk crystallinity of high gallium content CIGS shin films as well as cell performance can improved by the optimization of Se/metal flux ratio. However, cell performance was still low compared to ClGS cells with lower bandgap energy. Therefore, other factors may be causing the decrease in efficiency of devices with bandgap energies above 1.3 eV.