Colloidal lead-free Cs₂AgBiBr₆ double perovskite nanocrystals: Synthesis, uniform thin-film fabrication, and application in solution-processed solar cells

Recently developed lead-free double perovskite nanocrystals (NCs) have been proposed for the possible application in solution- processed optoelectronic devices. However, the optoelectronic applications of double perovskite NCs have been hampered due to the structural and chemical instability in the presence of polar molecules. Here, we report a facile strategy for the synthesis and purification of Cs₂AgBiBr₆ double perovskite NCs that remained stable even after washing with polar solvent. This is realized with our efficient colloidal route to synthesize Cs₂AgBiBr₆ NCs that involve stable and strongly coordinated precursor such as silver- trioctylphosphine complex together with bismuth neodecanoate, which leads to a significantly improved chemical and colloidal stability. Using layer-by-layer solid-state ligand exchange technique, a compact and crack-free thin film of Cs₂AgBiBr₆ NCs were fabricated. Finally, perovskite solar cells consisting of Cs₂AgBiBr₆ as an absorber layer were fabricated and tested.