Többens, D.M.; Gurieva, G.; Levcenko, S.; Unold, T.; Schorr, S.: Temperature dependency of Cu/Zn ordering in CZTSe kesterites determined by anomalous diffraction. Physica Status Solidi B 253 (2016), p. 1890-1897
10.1002/pssb.201600372
Abstract:
Low-temperature cation ordering is emerging as a critical factor limiting the efficiency of CZTSSe kesterite photovoltaic materials. By means of direct determination of the site occupancies from anomalous X-ray powder diffraction data at the Cu- and Zn-absorption edges, the ordering of Cu(I) and Zn(II) in B-type Cu2ZnSnSe4 (CZTSe) kesterite upon annealing at temperatures below 203(6) °C is demonstrated. Anomalous X-ray diffraction on the Cu- and Zn-K absorption edges allows determination of the distribution of isoelectric Cu(I) and Zn(II) over the crystallographic sites in a B-type CZTSe kesterite powder. By Rietveld refinement the quantitative determination of both Cu- and Zn-occupancy for all relevant sites is achieved. From this, the temperature dependency of a structure-based, quantitative order parameter is determined. The critical temperature of the phase transition is confirmed at 203(6) °C. The ordering mechanism is in agreement with a transition from disordered to ordered kesterite. The photoluminescence band maximum shows a closely related temperature dependency, directly demonstrating the effect of cation ordering on the optical properties of CZTSe.