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.