Determination of charge carrier collecting regions in chalcopyrite heterojunction solar cells by electron-beam-induced current measurements

The depth-dependent experimental collection functions F(z) of solar cells with CuInS2, CuGaSe2 and CuInSe2 absorber layers are derived from planar electron-beam-induced current (EBIC) measurements. It is shown that F(z) for CuInS2 and CuGaSe2 cells can be interpreted by a simple heterojunction model. For CuInSe2 cells, however, a near-interface region with modified experimental collection function is found, which is possibly due to an ordered vacancy compound formed at the surface. Moreover, high values of F(z) for minority carriers generated near the backcontact of the CuInSe2 cell are indicated. This can be interpreted by either the implementation of a backsurface field in these devices or perpendicular junctions at grain boundaries.