Abstract
Kesterite based materials are being researched and developed as affordable, efficient, and mechanically flexible absorber materials for thin film photovoltaics. Both (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 based devices have shown great potential in overcoming some of the remaining challenges for further increasing the conversion efficiency of kesterite based solar cells. This study therefore investigates the long range crystallographic structure and the local atomic scale structure of technologically relevant thin films by means of grazing incidence X-ray diffraction and low temperature X-ray absorption spectroscopy. As expected, the unit cell dimensions change about an order of magnitude more than the element specific average bond lengths. In case of Cu2Zn(Sn,Ge)Se4, the thin film absorbers show a very similar behavior as Cu2Zn(Sn,Ge)Se4 powder samples previously studied. Small amounts of residual S in the thin films were taken into account in the analysis and the results imply a preferential formation of Sn-S bonds instead of Ge-S bonds. In (Ag,Cu)2ZnSnSe4, the dependence of the Ag-Se and Cu-Se bond lengths on Ag/(Ag+Cu) might indicate an energetic advantage in the formation of certain local configurations.
Highlights
The quaternary compounds Cu2ZnSnSe4 and Cu2ZnSnS4 as well as some of their derivatives are well researched semiconductors (Giraldo et al, 2019)
Element specific average cation-Se bond lengths obtained from the low temperature Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) measurements of (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 thin film samples are plotted in Figure 2 as full symbols
The element specific average bond lengths of technologically relevant (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 thin films have been measured by low temperature EXAFS and compared to lattice parameters obtained from grazing incidence X-ray diffraction (GIXRD)
Summary
The quaternary compounds Cu2ZnSnSe4 and Cu2ZnSnS4 as well as some of their derivatives are well researched semiconductors (Giraldo et al, 2019). Atomic-Scale Structure of Kesterite Films (Voc) as a main culprit (Giraldo et al, 2019; Nazligul et al, 2020) This Voc deficit and the low conversion efficiency may be directly connected to intrinsic properties of the bulk material. This work uses Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) to determine the element specific average bond lengths for all cations in technologically relevant (Ag,Cu)2ZnSnSe4 and Cu2Zn(Sn,Ge)Se4 thin films This method has been successfully applied to both kesterite (Zalewski et al, 2010; Ritter et al, 2020) and chalcopyrite (Eckner et al, 2013; Schnohr, 2015) materials to probe for subtle differences in atomic scale structure as a function of elemental concentrations. X-ray diffraction was employed to measure the lattice parameters of the samples and to evaluate the change of the long range crystallographic structure with changing alloy composition
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
