Monovalent Charge Compensation Enables Efficient Lanthanide‐Based Near‐Infrared Perovskite LEDs

• Published in: Advanced functional materials Vol. 33; no. 45
• Main Authors: Yu, Yan‐Jun, Wang, Hong‐Shuai, Pan, Jia‐Lin, Li, Sheng‐Nan, Shen, Wan‐Shan, Cheng, Shu‐Ning, Jin, Lu‐Jie, Wang, Ya‐Kun, Li, You‐Yong, Liao, Liang‐Sheng
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01-11-2023
• Subjects: Alloying; charge compensation; Distortion; Efficiency; electroluminescence beyond 950 nm; Emissions control; Erbium; lanthanide alloying; lattice distortions; Lattice vacancies; Lead; Light emitting diodes; Materials science; Nanocrystals; Near infrared radiation; perovskite quantum dots; Perovskites; Phase stability; Quantum dots; Quantum efficiency; Sodium; Structural stability; Ytterbium
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202305125

Lanthanide ions (Yb3+ or Er3+) alloying of CsPb(Cl1‐xBrx)3 quantum dots (QDs) to emit approaching 1000 nm show promise in near‐infrared light‐emitting diodes (NIR‐LEDs). High Yb3+ alloying ratio increases the electroluminance efficiency of emission at 990 nm and enables high external quantum efficiency (EQE) of NIR‐LEDs, however, the high alloying ratio also results in inferior material stability and PLQY drop because of Yb3+‐induced nanocrystal precipitation. This study finds that the heavy alloying of Yb3+ ions causes lattice distortion and coherent energy reduction of Yb3+: CsPb(Cl1‐xBrx)3 QDs, induced by two Yb3+ ions replacing three Pb2+, which leads to the collapse of the octahedral structure in ambient conditions. It posits that spontaneous monovalent ion (Na+) alloying can address the trade‐off between material stability and emission intensity. The Na+ occupies the vacancy of Pb2+ ions, relaxing the distortion in the lattice and improving the phase stability of octahedral structure, and this optimized structure in turn allows a higher Yb3+ alloying ratio. Stability measurements show that the Na+/Yb3+ co‐alloyed films show ten‐fold higher material stability and 2.0‐fold emission efficiency related to controls. It reports that as a result Na+/Yb3+ co‐alloyed NIR‐LEDs have an EQE of 6.4% at 990 nm, which is among the highest perovskite NIR‐LEDs beyond 950 nm.
In this study, the structure of Yb3+‐doped perovskite nanocrystals is stabilized by modifying Na+ ions in the crystal lattice, and solving the issue of poor structural stability at high Yb3+ doping concentration. It reports near‐infrared light‐emitting diodes that provide an external quantum efficiency of 6.4% at 990 nm, fully 1.3‐fold as high as a pristine sample.