Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge. (1st June 2018)

• Record Type: Journal Article
• Authors: Robert, Erika V.C.; Gunder, René; de Wild, Jessica; Spindler, Conrad; Babbe, Finn; Elanzeery, Hossam; El Adib, Brahime; Treharne, Robert; Miranda, Henrique P.C.; Wirtz, Ludger; Schorr, Susan; Dale, Phillip J.
• Is Part Of: Acta materialia. Volume 151(2018)
• Page Start: 125
• Page End: 136
• Publication Date: 2018-06-01
• Subjects: Inorganic materials -- Semiconductors -- Thin films -- Alloys; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2018.03.043
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Cu2 Sn1- x Ge x S3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2 Sn1- x Ge x S3 films are prepared from x = 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2 SnS3 and Cu2 GeS3 . For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x = 0 to x = 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 10 18 cm −3 . These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure. Graphical abstract: Image 1