Octadecene-free colloidal synthesis of CsPbI₃ nanocrystals with improved size, shape and phase control

Cesium lead triiodide (CsPbI₃) colloidal nanocrystals (NCs) attract significant attention due to their potential for optoelectronic applications. However, they are prone to degrade to the non-photoactive phase (δ-CsPbI₃), posing a considerable challenge for industrial use. While many strategies to improve their stability have been explored, the effect of the solvent used during synthesis on the properties of the NCs has received much less attention. This study examines the replacement of the ubiquitously used solvent 1-octadecene (ODE), known to polymerize under mild to high temperatures (120-320 °C), with the less reactive alternative octadecane (ODA). We show that ODA can affect the crystalline growth, size distribution, and stability of CsPbI₃ colloidal NCs. While both ODE and ODA form mixtures of cubic α- and orthorhombic γ-CsPbI₃ NCs, each phase's prevalence differs depending on the solvent. The use of ODE led to primarily α-phase particles with large polydispersity. In contrast, ODA resulted in a significantly narrower size distribution and a prevalence of γ-CsPbI₃ NCs, which are considered more stable. Consequently, we observed improved stability of thin CsPbI₃ NC films without further additives or encapsulation procedures. Our work highlights the critical role of the solvent in the synthesis procedure in impacting the NCs' properties and stability.