Mechanochemical synthesis of the lead-free double perovskite Cs2[AgIn]Br6 and its optical properties

Joachim Breternitz,Susan Schorr,Hannes Hempel,Galina Gurieva,Alexandra Franz,Andreas Hoser,Sergiu Levcenko

doi:10.1088/2515-7655/ab155b

Abstract

Hitting hard on the binary halides yields in the formation of Cs2[AgIn]Br6. The lead-free double perovskite marks, although not usable itself, a further step forward in finding sustainable and durable perovskite materials for photovoltaic applications. Cs2[AgIn]Br6 is one of the prominent examples of double perovskites materials that have been suggested to circumvent the use of lead compounds in perovskite solar cells. We herein report the successful synthesis of the material as bulk powder using a mechanochemical approach. It crystallises in an elpasolite-type structure, an ordered perovskite superstructure, with a cell parameter of a = 11.00 Å. However, the compound exhibits a relatively large optical bandgap of 2.36 eV and is unstable under illumination, which impedes its use as solar absorber material at this early stage. Still, substitution of lead and the potential of this synthesis method are promising as well as the fruitful combination of theoretical considerations with experimental materials discovery.

Highlights

The X-ray diffraction pattern of the reaction product showed a pattern of mediocre quality (Figure 1a), which is mainly due to the small coherent domain size, as is characteristic for mechanochemical syntheses.[17]
We were able to perform a Rietveld refinement of the compound in an elpasolite type structure (Figure 1b) using Jana2006,[20] which is adopted by the analogous chloride compound Cs2[AgIn]Cl6.[9]. The full details of the Rietveld refinement may be found in the ESI (Figure S1 and S2 and Table S1 – Table S14)
The difference in cell parameters Δa = 0.52 Å between the bromide compound reported here and the chloride compound synthesized by Volonakis et al.[9] coincides very closely with the difference in atomic radii 2∙Δd = 4∙Δr = 0.6 Å

Summary

Introduction

The X-ray diffraction pattern of the reaction product showed a pattern of mediocre quality (Figure 1a), which is mainly due to the small coherent domain size, as is characteristic for mechanochemical syntheses.[17]. This was further confirmed in a temperaturedependent X-ray diffraction measurement, where the sample was heated under nitrogen gas flow (Figures S6-S8). The powder pattern does neither match to the starting materials, nor to the phases identified as competing phases within the system.[7,8] we were able to perform a Rietveld refinement of the compound in an elpasolite type structure (Figure 1b) using Jana2006,[20] which is adopted by the analogous chloride compound Cs2[AgIn]Cl6.[9] The full details of the Rietveld refinement may be found in the ESI (Figure S1 and S2 and Table S1 – Table S14).

Results

Conclusion