Aqueous Synthesis of Ultrastable Dual-Color-Emitting Lead-Free Double-Perovskite Cs2SnI6 with a Wide Emission Span Enabled by the Size Effect

Inthis work, we develop a green-route approach for thesynthesis of lead-free double-perovskite Cs2SnI6 powder and nanocrystals (NCs). Lead-free perovskites are promising materials for thefunctionalitiesof optoelectronic devices and systems. In this work, we develop agreen-route approach for the synthesis of lead-free double-perovskiteCs(2)SnI(6) powder and nanocrystals (NCs). An environmentallyfriendly aqueous solution is used to prepare the Cs2SnI6 powder at room temperature, and ultrasonicating the Cs2SnI6 powder in hexane yields the Cs2SnI6 NCs. The photoluminescence (PL) analysis revealsband gaps of 1.3 and 2.8 eV for the Cs2SnI6 powderand NCs, respectively. The Cs2SnI6 powder exhibitsa remarkable photothermal effect driven by a laser of 785 nm withelectric voltage ranging from 0.31 to 0.36 V, and the PL peak experiencesa blueshift of 940 to 934 nm. Increasing temperature from 30 to 90 degrees C causes a blueshift of the PL peak of the Cs2SnI6 powder with an apparent energy barrier of 1.298 eV for thermalquenching. The Cs2SnI6 NCs exhibit a PL peakcentered at 440 nm and a photoluminescence quantum yield of similar to 7%at room temperature and have a long-term stability over 50 days. Theanomalous behavior of the dual-color emission of the perovskite Cs2SnI6 is likely attributed to the size dependenceof the dielectric constant.