The role of growth temperature and Se flux on Cu(In,Ga)Se2 thin film deposited on a stainless steel substrate and solar cell

The role of growth temperature and Se flux on Cu(In,Ga)Se2 (CIGS)/Mo deposited on stainless steel substrates without a barrier is investigated by combined use of secondary ion mass spectroscopy, scanning electron microscopy and Raman spectroscopy. Fe atoms diffuse into the CIGS film with an increasing slope toward the CIGS front surface and the CIGS/Mo interface at 500 °C. High Se flux can increase the grain size and depress the formation of group III-rich phases on the surface and grain boundaries of the CIGS film, reducing Fe content in the surface region of the CIGS film and grain boundaries, which results in the increase of open circuit voltage (Voc) and fill factor (FF). Meanwhile, Jsc also significantly increases for high Se flux. In this case, a 12.1%-efficient CIGS solar cell on stainless steel without a diffusion barrier and Na supply is obtained. The influence of diffusing Fe on a solar cell with different Se fluxes is further discussed in detail. (paper)