Ga/(Ga + In) grading effects on ultra-thin (UT) CIGS solar cell

Here, we specifically address device performance in ultra-thin CIGS (UT UT-CIGS) films with thickness around 500 nm by systematically implementing varying in in-depth grading of the GGI (Ga/(Ga+In)ratio). By adjusting the GGI slope, the open circuit voltage can be significantly improved, indicating a reduction of recombination in the quasiquasi-neutral region and at the back contact; the photocarrier collection efficiency over the whole absorption spectrum enhanced significantly with an aggressive GGI profile. Ultimately, a power conversion efficiency of UT-CIGS device over 12% with thickness around 500 nm by carefully applying a an appropriate GGI profile was demonstrated.