Nanometer-scale electronic and microstructural properties of grain boundaries in Cu(In,Ga)Se 2

Abstract

Despite many recent research efforts, the influence of grain boundaries (GBs) on device properties of CuIn 1−xGa xSe 2 solar cells is still not fully understood Here, we present a microscopic approach to characterizing GBs in polycrystalline CuIn 1−xGa xSe 2 films with x = 0.33. On samples from the same deposition process we applied methods giving complementary information, i.e., electron backscatter diffraction (EBSD), electron-beam induced current measurements (EBIC), conductive atomic force microscopy (c-AFM), variable-temperature Kelvin probe force microscopy (KPFM), and scanning capacitance microscopy (SCM). By combining EBIC with EBSD, we find a decrease in charge-carrier collection for non-∑3 GBs, while ∑ 3 GBs exhibit no variation with respect to grain interiors. In contrast, a higher conductance of GBs compared to grain interiors was found by c-AFM at low bias and under illumination. By KPFM, we directly measured the band bending at GBs, finding a variation from − 80 up to + 115 mV. Depletion and even inversion at GBs was confirmed by SCM. We comparatively discuss the apparent differences between the results obtained by various microscopic techniques.