Calculated quantum efficiency of polycrystalline CIGSe/CdS/ZnO solar cells at a wavelength of the incident light of 1000 nm. The energy position of the donor type defect at the grain boundary (trap level) has been varied to modify the band bending towards the grain boundary. The dashed horizontal lines indicate the quantum efficiency without grain boundary (1D case). The dotted vertical line marks the mid-gap position. The absorber grain radius is 1 μm and the carrier lifetimes are 1 ns.