Preparation and Characterization of Cu2Zn(GexSn1-x)Se4 Thin-films from Sputtered Elemental Precursors. Issue 1670 (2014)

• Record Type: Journal Article
• Authors: Jan, Antony; Yee, Yesheng; Clemens, Bruce M.
• Is Part Of: MRS proceedings. Issue 1670:(2014)
• Publication Date: 2014
• Subjects: photovoltaic, -- thin film, -- x-ray diffraction (XRD); Electrical engineering -- Congresses; Physics -- Congresses; Materials -- Research -- Congresses; Materials science -- Congresses; 620.11
• DOI: 10.1557/opl.2014.418
• Languages: English
• ISSNs: 0272-9172

Abstract

ABSTRACT: Thin-film absorber layers for photovoltaics have attracted much attention for their potential for low cost per unit power generation, due both to reduced material consumption and to higher tolerance for defects such as grain boundaries. Cu2 ZnGeSe4 (CZGSe) comprises one such material system which has a near-optimal direct band gap of 1.6 eV for absorption of the solar spectrum, and is made primarily from earth-abundant elements. CZGSe metallic precursor films were sputtered from Cu, Zn, and Ge onto Mo-coated soda lime glass substrates. These were then selenized in a two-zone close-space sublimation furnace using elemental Se as the source, with temperatures in the range of 400 to 500 C, and at a variety of background pressures. Films approximately 1-1.5 µm thick were obtained with the expected stannite crystal structure. Next, Cu2 ZnSnSe4 (CZTSe), which has a direct band gap of 1.0 eV, was prepared in a similar manner and combined with CZGSe as either compositionally homogeneous or layered absorbers. The compositional uniformity of selenide absorbers made by selenizing compositionally homogeneous Cu-Zn-Ge-Sn precursor layers was determined and the band gap as a function of composition was investigated in order to demonstrate that the band gap is tuneable for a range of compositions. For layered Cu-Zn-Ge/Cu-Zn-Sn precursor films, the composition profile was measured before and after selenization to assess the stability of the layered structure, and its applicability for forming a band-gap-graded device for improved current collection.