Schöppe, P.; Gurieva, G.; Giraldo, S.; Martinez-Criado, G.; Ronning, C.; Saucedo, E.; Schorr, S.; Schnohr, C.S.: Discrepancy between integral and local composition in off-stoichiometric Cu2ZnSnSe4 kesterites : A pitfall for classification. Applied Physics Letters 110 (2017), p. 043901/1-5
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High-efficiency kesterite-based thin film solar cells typically feature Cu-poor, Zn-rich absorbers although secondary phases occur easily in non-stoichiometric Cu2ZnSnSe4. We therefore applied high-resolution X-ray fluorescence analysis using a synchrotron nanobeam to study the local composition of a CZTSe cross section lamella cut from a sample with an integral composition of Zn/Sn ¼ 1.37 and Cu/(ZnþSn) ¼ 0.55. We find submicrometer-sized ZnSe-, SnSe/SnSe2-, and even CuSe/Cu2Se-like secondary phases, while the local compositions of the kesterite are highly Zn-rich yet barely Cu-poor with 1.5 Zn/Sn 2.2 and Cu/(ZnþSn) 1.0. Consequently, great care must be taken when relating the integral composition to other material properties including the device performance.