Phase Identification and Control of Thin Films Deposited by Co-Evaporation of Elemental Cu, Zn, Sn, and Se

Kesterite thin films [(i.e., Cu ₂ZnSn(S,Se) ₄ and related alloys] have been the subject of recent interest for use as an absorber layer for thin film photovoltaics due to their high absorption coefficient (>10 ⁴ cm ^-1), their similarity to successful chalcopyrites (like CuInxGa _1-xSe ₂) in structure, and their earth-abundance. The process window for growing a single-phase kesterite film is narrow. In this work, we have documented, for our 9.15-efficient kesterite co-evaporation process, (1) how appearance of certain undesirable phases are controlled via choice of processing conditions, (2) several techniques for identification of phases in these films with resolution adequate to discern changes that are important to device performance, and (3) reference measurements for those performing such phase identification. Data from x-ray diffraction, x-ray fluorescence, Raman scattering, scanning electron microscopy, energy dispersive spectroscopy, and current-voltage characterization are presented.