In Situ and Ex Situ Investigations of KF Postdeposition Treatment Effects on CIGS Solar Cells

Abstract

In situ and ex situ characterization were performed to assess the effects of potassium fluoride postdeposition treatment (KF PDT) on Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGS) films and solar cells. Real-time spectroscopic ellipsometry enabled the in situ observation of the modification of the CIGS dielectric function and surface roughness thickness during KF PDT. In addition, deep-level transient spectroscopies (DLTS) and deep-level optical spectroscopies and scanning-DLTS enabled the identification of the nature and location of trap levels. Two main traps were present in both films near E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> + 0.56/0.61 eV and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</sub> + 0.99 eV, but with clearly lower concentrations for the latter in the KF PDT film. Finally, devices were fabricated, and higher efficiencies were found for the KF PDT devices. SCAPS modeling indicates that the traps identified by deep-level spectroscopies are in part responsible for these changes.