Chalcopyrite/defect chalcopyrite heterojunctions on the basis of CuInSe2

Abstract

A new model for the formation of heterojunctions in polycrystalline CuInSe₂ thin films on the basis of surface analysis experiments is presented. In situ photoemission measurements of CuInSe₂ clearly show the existence of an In‐rich n‐type surface layer on samples relevant for solar‐cell devices. Furthermore, this layer has been identified as an ordered vacancy compound (OVC) with a band gap of about 1.3 eV. The previous model of the CuInSe₂/CdS solar cell with a p‐n heterojunction between p‐type CuInSe₂ and n‐type CdS is replaced by the model of a chalcopyrite/defect chalcopyrite heterojunction between p‐type bulk CuInSe₂ and the In‐rich n‐type OVC. The existence of this junction was proven directly by evaporating an ohmic metal contact onto the surface n‐type layer and measuring the spectral quantum efficiency and electron‐beam‐induced current of this device. The band offsets of CuInSe₂‐based devices have been determined.