All-inorganic perovskite light-emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy-level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr-based PeLED with an inverted architecture using lithium-doped TiO nanoparticles as the electron transport layer (ETL). The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A, a luminance efficiency of 2210 cd m, and a low turn-on voltage of 2.3 V. The turn-on voltage is one of the lowest values among reported CsPbBr-based PeLEDs. A 7-fold increase in device efficiencies has been obtained for lithium-doped TiO compared to that for undoped TiO-based devices.

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Although all-inorganic perovskite light emitting diodes (PeLED) have satisfactory stability under an ambient atmosphere, producing devices with high performance is challenging.

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performance such as low operation voltages, good device stability, and high color quality. [1][2][3] However, the deep valence band (VB) level of QDs results in a large band offset for hole injection and limits the electroluminance (EL) efficiency. [4][5][6][7][8] To overcome the hindrance, multi-holetransporting layers (multi-HTLs) have been used to increase the external quantum efficiency (EQE) up to 20.5%, bringing it closer to the theoretical maximum of 21%. [9][10][11][12] Nevertheless, the number of transport layers can limit the device performance in a multi-HTL device because of charge imbalance and accumulation. [11,13,14] In this regard, HTL materials with proper band alignment and precise thickness are required to maximize the hole diffusion in materials. [15] In particular, the unequal energy barriers at both sides of QD layer cause imbalanced charge injection (CI) into the QD layer, leading to charge density accumulation at the interfaces of HTL/QDs and QD/electron transport layer (ETL). [16] The charge imbalance will further lead to luminance quenching via the nonradiative Auger recombination mechanism. [17] Depending on the density of available electrons and holes, the charge accumulation facilitates Förster resonance energy transfer (FRET), which is a dominating undesirable process limiting the QLED efficiency. [18,19] Furthermore, the limited carrier injection normally results in instability and higher operation voltage of Development of quantum dots (QDs) based light-emitting diodes (QLEDs) is driven by attractive properties of these fluorophores such as precise Gaussian distribution, tunable emission, and facile solution processability. The performance of QLED devices is limited by intrinsic factors such as luminance quenching in quantum dots due to imbalanced carrier injection predominantly caused by a large hole injection barrier as well as by extrinsic processes such as nonradiative recombination at active layer interfaces.The Auger recombination problem is overcome by charge siphoning at the interfaces between QDs and charge-transporting material. A simplest trilayer (p-i-n) LED structure is fabricated using an all-solution processing method: a carefully engineered p-type polymeric hole transport layer with a gradient work function is incorporated. The gradient work function creates the cascading energy levels from the moderate Fermi level anode to the deeplying valence band level of QDs. As a result, the QLEDs exhibit significantly improved external quantum efficiencies and luminous efficiencies of 15.9% and 31.8 cd A −1 , 17.4% and 59.3 cd A −1 , and 12.8% and 14.4 cd A −1 for red, green, and blue light-emitting devices, respectively. It is expected that the concept demonstrated here will facilitate the design and development of efficient solution-processible QLEDs for full-color displays.