Abstract
Abstract All-inorganic CsPbBr3 perovskite is an attractive emission material for high-stability perovskite light-emitting diodes (PeLEDs), due to the high thermal and chemical stability. However, the external quantum efficiencies (EQEs) of CsPbBr3 based PeLEDs are still far behind their organic–inorganic congeners. Massive defect states on the surface of CsPbBr3 perovskite grains should be the main reason. Lewis base additives have been widely used to passivate surface defects. However, systematic investigations which relate to improving the passivation effect via rational molecule design are still lacking. Here, we demonstrate that the CsPbBr3 film’s optical and electrical properties can be significantly boosted by tailoring the hardness–softness of the Lewis base additives. Three carboxylate Lewis bases with different tail groups are selected to in-situ passivate CsPbBr3 perovskite films. Our research indicates that 4-(trifluoromethyl) benzoate acid anion (TBA−) with the powerful electron-withdrawing group trifluoromethyl and benzene ring possesses the softest COO− bonding head. TBA− thus acts as a soft Lewis base and possesses a robust combination with unsaturated lead atoms caused by halogen vacancies. Based on this, the all-inorganic CsPbBr3 PeLEDs with a maximum EQE up to 16.75% and a half-lifetime over 129 h at an initial brightness of 100 cd m−2 is thus delivered.
Highlights
Metal halide perovskite films fabricated by solutionprocessed method is promising candidates for the next-generation display and light-emitting devices contributed to their high photoluminescence quantum yield (PLQY), tunable bandgap, excellent color purity, and simple preparation process
Defect state densities of 1.52 × 1017, 1.36 × 1017, 7.26 × 1016, and 6.01 × 1016 cm−3 were extracted for original CsPbBr3 films and CsPbBr3 films incorporated with hexanoic acid sodium salt (HAS), BA, and TBAS, respectively
Our result demonstrates that anionic Lewis base TBA−, containing electron-withdrawing groups, possesses a soft carboxylate anion (COO−) binding head
Summary
Metal halide perovskite films fabricated by solutionprocessed method is promising candidates for the next-generation display and light-emitting devices contributed to their high photoluminescence quantum yield (PLQY), tunable bandgap, excellent color purity, and simple preparation process. Typical Lewis base molecules such as pyridine, thiophene [18], ethylenediamine (EDA) [19], and trioctylphosphine oxide (TOPO) [2] have been used to passivate perovskite solar cells or LED devices, which achieve significant photoelectric properties improvement Most of these passivation strategies were carried out through a post treatment process, where a considerable amount of defect states still existed inside the resulting films. To reveal the underlying connection and propose a universal strategy for designing the additive molecules, we introduced three carboxylate sodium salts with different molecule structures into the CsPbBr3 perovskite precursor for in-situ passivating the film’s defect states These carboxylate sodium salts include hexanoic acid sodium salt (HAS), benzoic acid sodium salt (BAS) and 4-(trifluoromethyl) benzoate acid sodium salt (TBAS). A half-lifetime up to 129 h is obtained at an initial brightness of 100 cd m−2
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