Non-toxic, all-inorganic perovskite light absorbers received great attention in recent years due to their potential to replace lead-containing perovskite materials in photovoltaics. Regardless of the potential of lead-based halide perovskites, their application on large scale is challenging, mainly due to the toxicity of lead and stability issues. Lead-free absorbers, such as the double perovskite Cs₂AgBiBr₆ as a prominent representative, offer high stability and auspicious optoelectronic properties. Cs₂AgBiBr₆ has been studied intensively in the past few years. Various researchers pre-synthesize this absorber as powder by a synthesis method first suggested by Slavney et al. in 2016 [1] and the resulting absorber powder is further dissolved to render a thin film deposition. Although this method is well reproducible, it is only suitable for the lab-scale synthesis of Cs₂AgBiBr₆, with yields usually in the range of a few grams. Besides this rather small yield, the synthesis requires exceptional safety precautions.

Within this work, we present an alternative synthesis approach for Cs₂AgBiBr₆ powder, namely via spray-drying [2]. During spray-drying, the perovskite phase forms by in-situ crystallization upon drying of the atomized precursor solution. The product is compared to the conventionally synthesized absorber. XRD and Raman analyses confirm the product’s phase-purity, whereas UV-Vis spectroscopy confirms the desired bandgap. Furthermore, absorber films in single-junction perovskite solar cells are successfully produced from both absorber powders, clearly demonstrating the suitability of spray-drying as an alternative synthesis method.

Moreover, we investigated the Bi-substitution by Sb to reduce the perovskite’s original bandgap of ~2.2 eV achieving better suitability as top-cell absorber in perovskite-silicon tandem devices [3]. Spray-drying enabled a fast screening and identification of the substitution limit, and could overcome limitations of the conventional synthesis for the Sb-substituted Cs₂AgBiBr₆.

As a side notice, we can tell that we additionally investigated the lead-free perovskites Cs₃Bi₂Br₉ and Cs₃Bi₂I₉. Besides these, lead-based halide perovskites have been synthesized successfully via spray-drying, too. With the prospect of an industrial scale photovoltaic industry, the demand for high-quality perovskite materials will most likely increase in future. Therefore, spray-drying could pave the way for an easy adaptation to increasing production volumes of perovskite powders in general owing to its suitability as screening method and its capability of producing large amounts of powders.