Can Grain Boundaries Improve the Performance of Cu(In,Ga)Se2 Solar Cells?

K. TARETTO; U. RAU

MATERIALS RESEARCH SOCIETY SYMPOSIA PROCEEDINGS

Thin Film Compound Semiconductor Photovoltaics

Lugar: Pittsburgh (EEUU); Año: 2007 p. 9 - 15

0272-9172

Two-dimensional numerical device simulations investigate the influence of grain boundarieson the performance of Cu(In,Ga)Se2 solar cells focussing on the question whether or notgrain boundaries can improve the efficiency of those devices. The results unveil the followingstatements: (i) The mere introduction of a grain boundary by adding localized defects into a device that has a high performance from the beginning is not beneficial. (ii) Polycrystalline solarcells can outperform monocrystalline ones, if the total number of defects is equal in both devicesi.e. a given number of recombination centers is better dealt with if these defects are concentratedat the grain boundary rather than homogeneously distributed in the bulk. (iii) A significant improvement of carrier collection via the grain boundaries is found if the bulk of the devices is assumed as relatively poor. In this situation, addition of defects that are not much recombination active but provide a large charge density at the grain boundaries can improve the device performance. (iv) Almost perfect passivation of grain boundaries by an internal band offset in the valence band requires an internal barrier of at least to 300 meV.