Point defects in Cu 2 ZnSnSe 4 (CZTSe): Resonant X‐ray diffraction study of the low‐temperature order/disorder transition (Phys. Status Solidi B 9/2017)

Cu 2 ZnSnSe 4 (CZTSe) gained interest as an earth abundant solar absorber material; however, thin films of CZTSe are known to have high levels of Cu Zn and Zn Cu defects. The implication of this disorder is often debated, but it may contribute to the open circuit voltage deficit in CZTSe films, which has prevented these materials from becoming commercially viable. To explore this disorder, Schelhas et al. (article no. 1700156 ) have used resonant X‐ray diffraction (REXD), a site and element specific probe of long‐range order to determine the level of Cu Zn and Zn Cu defects in CZTSe thin films annealed just below and quenched from just above the order/disorder transition temperature. The REXD technique utilizes the increase in scattering intensity of atoms near their resonant edge. The plot on the cover shows the idealized case of fully ordered Cu/Zn (black line – right structure), and fully disordered (red line – left structure). In this work, Schelhas et al. explore the Cu/Zn order in CZTSe thin films and comment on discrepancies between the REXD results and previous studies that employ NMR and optical spectroscopies. The authors present a structural model of the antiphase boundaries (pink plane) to explain previous observations in the literature and point to the importance of developing alternative approaches to CZTS processing.