Lead-Free Direct Bandgap Double Perovskite Nanocrystals with Bright Dual-Color Emission

摘要： Lead-free double perovskite nanocrystals (NCs), i.e. Cs2AgInxBi1?xCl6 (x = 0, 0.25, 0.5 0.75 and 0.9), that can be tuned from the indirect bandgap (x = 0, 0.25 and 0.5) to the direct bandgap (x = 0.75 and 0.9) are designed. Direct-bandgap NCs exhibit 3 times greater absorption cross-section, lower sub-bandgap trap states, and >5 times photoluminescence quantum efficiency (PLQE) compared with those observed for indirect bandgap NCs (Cs2AgBiCl6). A PLQE of 36.6% for direct bandgap NCs is comparable to those observed for lead-perovskite NCs in the violet region. Besides the band edge violet emission, the direct bandgap NCs exhibit bright orange (570 nm) emission. Density functional theory calculations suggesting forbidden transition is responsible for the orange emission, which is supported by time resolved PL and PL excitation spectra. The successful design of lead-free direct bandgap perovskite NCs with superior optical properties opens the door for high performance lead-free perovskite optoelectronic devices.