Secondary and polymorphic phase behavior of thin film CuInSe2 : ramifications on the device performance

The microstructure of polycrystalline thin film CuInSe₂ is investigated by spectrophotometry, X-ray diffraction, and transmission electron diffraction as a function of composition and relevant processing parameters. The inter- and intragranular microstructure is defined as a compositionally and temperature-dependent polycrystalline aggregate mixture of CuInSe₂ and Cu_x Se/In_ySe minor phases at intragranular and grain boundary positions. The core crystallite exhibits order-disorder and a CuInSe₂-CuIn₂Se_3.5 phase separation and/or solid solution. The implications for device performance are dependent on the extent of band-bending and interface states at phase boundaries and on the filling extent of minor phase precipitates. The Cu-poor CuIn₂Se_3.5 phase may be suitable for device application