Nanometer-scale electronic and microstructural properties of grain boundaries in Cu(In,Ga)Se2

Despite many recent research efforts, the influence of grain boundaries (GBs) on device properties of CuIn1-xGaxSe2 solar cells is still not fully understood Here, we present a microscopic approach to characterizing GBs in polycrystalline CuIn1-xGaxSe2 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-Sigma 3 GBs, while Sigma 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. (C) 2011 Elsevier B.V. All rights reserved.