Simulation of the effect of grain-boundaries in backside-passivated CIGS solar cells

We carry out numerical 3D simulations of CIGS cells with back-side Al
₂
O
₃
passivation and point contact openings in the presence of grain boundaries in the absorber. We consider CIGS cells with different absorber thickness, from 0.35 to 3 μm. For thinner absorbers ( 1 μm or less) we observe that GBs terminating on the Al
₂
O
₃
are completely or almost completely passivated, while the effectiveness of the passivation decreases for thicker absorbers. GBs terminating on the point contact, instead, significantly lower the efficiency, regardless of absorber thickness. The presence of grain boundaries and the dimension of grains should therefore be taken into consideration when optimizing the back-side point contact array geometry.