Enhanced Flexibility and Stability of Emissive Layer Enable High‐Performance Flexible Light‐Emitting Diodes by Cross‐Linking of Biomass Material

Abstract

Flexible perovskite light‐emitting diodes (LEDs) have been highly expected to realize advanced wearable optoelectronic applications due to the excellent optoelectronic properties of perovskites. However, the poor water and oxygen stability and limited flexibility of perovskites prevent their commercialization and applications in flexible LEDs. Herein, the low‐cost and green biomass materials‐ethyl cellulose (EC) is added in the CsPbI3 nanocrystals (NCs), acting as a cross‐linker between neighboring halide octahedra through hydrogen bonds and PbO coordination bonds. It reduces the defect densities of NCs, leading to improved photoluminescence quantum yield. Simultaneously, the synergistic effect of efficient defect passivation and hydrophobic ether groups of EC significantly improve the environment stability of NCs. Additionally, the favorable flexibility of EC and cross‐linking between EC and perovskite NCs improve the deformation resistance of the perovskite layer with stable photoluminescence and negligible cracks after repeated bending. Consequently, flexible LEDs based on the EC‐passivated CsPbI3 NCs achieved a record external quantum efficiency of 12.1% and significantly enhanced operational stability. Moreover, the flexible LEDs show small luminance degradation after bending for 1000 cycles at a radius of 3 mm, and still retain high performance even after repeatedly bending at an ultrasmall bending radius of 1 mm.

Highly Stable and Efficient Light-Emitting Diodes Based on Orthorhombic γ-CsPbI3 Nanocrystals

“…Trap densities ( N t ) and charge carrier mobilities (μ) determined from the dark current–voltage characterization of hole-only and electron-only devices are provided in Figure S14. Derived from those measurements , and summarized in Figure F, the hole trap density decreases from 5.03 × 10 17 to 4.46 × 10 17 cm –3 , and the electron trap density decreases from 1.26 × 10 18 to 1.04 × 10 18 cm –3 along with the phase transformation from α-CsPbI 3 to γ-CsPbI 3 .…”

Spring‐Like Ammonium Salt Assisting Stress Release for Low‐Temperature Deposited FAPbI3 Films Toward Flexible Photovoltaic Application

“…In order to reduce the residual stress and enhance the flexibility of perovskite, polymer materials are widely utilized. [24][25][26][27][28] However, the interfacial contact between the polymer materials and the perovskite layer is poor due to the difference of the structure, which affects the transport of carriers and the stable output of performance. Therefore, we need to find a material which can reduce the density of trap states on the surface of the perovskite film, reduce the residual stress of the perovskite layer, and have good contact with the perovskite surface.…”

Bifunctional Molecule Enables High-Quality CsPb(Br/Cl)3 Nanocrystals for Efficient and Stable Pure-Blue Perovskite Light-Emitting Diodes

“…The sharp rise of the current density–voltage ( J – V ) curve relates to a trap-filled limit, where all the defects are occupied by charge carriers. By calculation (see the Supporting Information for details), the defect densities of pristine and optimized PeNC films are 2.57 × 10 17 and 1.97 × 10 17 cm –3 , respectively, confirming that the defect density of PeNC films can be substantially decreased with the use of PFTS …”

“…By calculation (see the Supporting Information for details), the defect densities of pristine and optimized PeNC films are 2.57 × 10 17 and 1.97 × 10 17 cm −3 , respectively, confirming that the defect density of PeNC films can be substantially decreased with the use of PFTS. 34 By observing the X-ray diffraction (XRD) spectra of the synthesized NCs (Figure 2a), one can see that both the pristine and optimized PeNCs have a cubic crystal structure, but the diffraction peaks of the optimized PeNCs slightly shift to a larger angle in comparison with the pristine PeNCs, demonstrating the lattice shrinkage of the PeNCs. 35 In addition, we noted that the diffraction peaks of the optimized PeNCs are narrower than those of the pristine PeNCs, implying the larger crystal grain size for the optimized PeNCs.…”