Consequences of Bandgap Shifts Resulting from Decreasing CIGS Thickness in CIGS Solar Cells

We investigated the effects on performance of reducing the thickness of CIGS solar cells. One of the important observations is that there is an apparent bandgap increase as the thickness is reduced. This is attributed to the details of our device fabrication and resulting Ga profile. AMPS simulations indicate that accompanying expected lowering of J_sc due to absorption losses, we should expect increases in V_oc and FF resulting in a net gain in efficiency. As we decrease thickness the losses that we observe in J_sc are larger than expected from absorption due to two factors: the unexpected bandgap increase and increased defect density at the junction interface. However, while AMPS predicts an increase of 13 mV in V_oc, the increase we observe is in the 20-30 mV range. J_sc´sfor one micron thick devices have also been increased to 30.5 mA/cm² which is somewhat above what is expected from simulations