Local built-in potential on grain boundary of Cu(In,Ga)Se2 thin films

Abstract

We report on a direct measurement of two-dimensional potential distribution on the surface of photovoltaic Cu(In,Ga)Se2 thin films using a nanoscale electrical characterization of scanning Kelvin probe microscopy. The potential measurement reveals a higher surface potential or a smaller work function on grain boundaries of the film than on the grain surfaces. This demonstrates the existence of a local built-in potential on grain boundaries, and the grain boundary is positively charged. The local built-in potential on the grain boundary is expected to increase the minority-carrier collection area from one to three dimensional. In addition, a work function decrease induced by Na on the film surface was observed.

Comparative study of the luminescence and intrinsic point defects in the kesterite Cu2ZnSnS4and chalcopyrite Cu(In,Ga)Se2Romero1, Du2, Teeter3 et al. 2011Phys. Rev. B20351220View full textAdd to dashboardCite

“…The predicted valence band offset caused by the removal of copper atoms from the boundary leads to the formation of a neutral barrier for holes that do not otherwise impede the electron transport and reduce recombination [22]. The existence of this neutral barrier has been confirmed experimentally by several methods [10,[23][24][25]. In our case, microluminescence measurements based on spectrum imaging revealed a redshift of the emission spectrum at grain boundaries.…”

Thin-film Sb2Se3 photovoltaics with oriented one-dimensional ribbons and benign grain boundaries

“…Typical examples are the carefully engineered Cu deficient GBs in CIGS solar cells 23,24 and a high temperature CdCl2 treatment for CdTe solar cells 24,25 .…”

Potential variations around grain boundaries in impurity-doped BaSi2 epitaxial films evaluated by Kelvin probe force microscopy

“…KFM revealed that random GBs have negative influences on solar cell performance compared to those with low R values in polycrystalline Si, 27,28 and that the electron-hole pairs are well separated at GBs in high-efficiency CIGS solar cells. [29][30][31] According to our previous work on the potential variations around the GBs using KFM, 32 the potentials were higher at GBs by approximately 30 meV than those in the BaSi 2 grain interiors in the undoped n-type BaSi 2 films, suppressing the charge carrier recombination at the GBs. This explains the reason why the minority-carrier diffusion length (ca.10 lm) is much longer than the average grain size of undoped n-BaSi 2 (ca.0.2 lm), 8 which is to be an active layer in a BaSi 2 pn junction solar cell.…”