Synthesis of lead-free iodide perovskites

Abstract

Lead halide perovskites are developed for light-absorbing applications (e.g., solar cells), but concerns about the toxicity of Pb have motivated the research of lead-free perovskites that might be equally as effective as the parent haloplumbates. One promising alternative family of materials consists of double perovskites in which two metals substitute the divalent Pb metal, for example with a monovalent metal and a trivalent metal. A prominent synthetic target are iodide double perovskites, which may display a bandgap much more suitable for solar-cell applications. The synthesis of iodide double perovskite is currently hindered by the crystallization of competing phases with low-dimensional structures with similar chemical composition as the double perovskites. This project proposes the hypothesis of moving away from standard solution methods by using microfluidic chips and thus avoiding competing phases. To do this, the chemical space of three iodide perovskites based on Cs and CH3NH3 as A-sites and Na, Ag, Bi, In and La as B/B’-sites (Cs2AgBiI6, (CH3NH3)2AgBiI6 Cs2AgInI6 and Cs2AgLaI6) was explored. Although it has not been possible to synthesize any iodide double perovskites, new compounds that have not yet been reported have been obtained such as (CH3NH3)InI4 and CsAgI2 as well as already reported ones such as Cs3Bi2I9, (CH3NH3) Bi2I9, CsInI4 and CsI3. It has also been observed that there is a tendency to obtain the same competitive phase for the cases of Bi and In in the B'-site (0D A3Bi2I9 and AInI4 respectively with A = Cs or CH3NH3). Moreover, it has also been observed that despite changing the elements of the B-site (Ag and Na), these did not interfere at all in the formation of the preferred phases in the cases of Bi and In in the B’-site but it did interfere when there was La in the B’-site. Finally, due to the high solubility of the starting reagents in the case of CH3NH3 in the A-site and La in the B’-site crystallization did not occur.