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

Abstract

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.

Polarity-Mediated Antisolvent Control Enables Efficient Lanthanide-Based near-Infrared Perovskite LEDs

“…We conducted the ICP measurements several times to ensure the repeatability and validity of the concentration and used the average value (three-time measurements) to indicate the Yb/Pb ratio. ICP-OES (Figure a) shows the average Pb and Yb concentration of control is 5.1 and 0.85 mg/mL, respectively, which coincides with the reported Yb/Pb ratio of ∼15% in the literature . By contrast, the Yb/Pb concentration of the treated films is 30.2% under the same solution concentration of 30 mg/mL.…”

“…This Yb/ Pb ratio is the highest among reported Yb 3+ :CsPb(Cl 1−x Br x ) 3 , and represents 1.75-fold higher than the previous record value. 23 We further verified the Yb 3+ ratio by using X-ray photoelectron spectroscopy (XPS, Supporting Figure 1) and transmission electron microscope energy-dispersive X-ray spectroscopy (TEM-EDX, Supporting Information, Figure 2), and the results are consistent with the ICP measurements.…”

“…In previous work, the highest Yb 3+ concentration is limited to 17.2% because of the existence of strongly confined quantum dots and inferior material stability with a high Yb 3+ alloying ratio, resulting in the collapse of the lattice and loss of the Yb 3+ concentrations. 23 By engineering the antisolvent ratio and overall solution polarity (details in the mechanism study part), we improve the Yb 3+ alloying ratio with a factor of 1.8 benefiting from improved size distribution and material stability. Due to the large increase of Yb 3+ , the 4f−4f transition channels are increased, resulting in an improved saturation limit in the 2 F 5/2 orbit of Yb 3+ .…”

“…22 However, a high amount of Yb 3+ alloying (>15%) in smallsize perovskite quantum dots results in additional lattice defects and poor material stability, posing limitations to the NIR-LED performance. 23 In this work, we report a polarity-mediated antisolvent manipulation strategy to resolve the trade-off between the Yb 3+ alloying ratio and material stability and enhance the NIR emission efficiency by increasing the Yb 3+ alloying ratio to a higher level. We found uniform perovskite matrix with improved crystallinity can be obtained by controlling the solution polarity: we reduced the solution polarity during the antisolvent precipitation process and optimized the antisolvent ratio to obtain the proportion of large, uniform, and heavily doped Yb control effect on the performance of Yb 3+ :CsPb(Cl 1−x Br x ) 3 QDs reveals there is an optimal polarity ratio to achieve the balance between ligand density, trap density and materials stability with high Yb 3+ alloying ratio, which is the key to enabling record-high EQE with improved operational stability.…”

Nanocrystals of divalent europium-doped CsPbCl3 perovskites: a novel optoelectronic material with dual-emissions

“…1–5 Recently, doping Ln 3+ ions into CsPbX 3 QDs has been proved to provide opportunities to modify the perovskite structure and expand the spectral emitting range from the visible to near-infrared region due to their abundant 4f energy levels and unique electronic configurations. 6–9 For instance, efficient quantum cutting luminescence with a PLQY close to 200% is observed in Yb 3+ -doped CsPb(Cl/Br) 3 QDs, and Ln 3+ doping or co-doping into CsPbX 3 can enable their potential applications in lighting and photovoltaics. 10–15…”