All-Solution-Processed Fabrication of Flexible Multicolor Quasi-2D Perovskite LEDs and Photodetectors on Unconventional Substrates (Elastomer, Paper, Textiles, etc.)

Owing to unique properties such as a tunable bandgap and strong optical absorption, perovskites hold great potential for optoelectronic device applications. Although significant progress has been made in developing high-performance LEDs and photodetectors (PDs) using perovskites, existing fabrication techniques based on rigid substrates fail to meet the growing demand for large-area flexible displays. In this work, we report all-solution-processed perovskite LEDs (PeLEDs) and photodetectors (PePDs) fabricated on various unconventional substrates commonly found in daily life, including paper, textiles, plastics, rubber, metal, and even 3D objects, using a versatile and low-cost approach, termed “Handwriting”. Compared to conventional spin-coating and vacuum-evaporation processes, this direct-writing approach enables mask-free patterning and allows even untrained individuals to “draw” a batch of high-performance LEDs/PDs in a time-efficient and energy-saving manner.<br/><br/>A significant challenge in implementing optoelectronic devices on paper and textiles is the rough surface morphology of yarn and cellulose fiber, which can lead to nonuniform film thickness and leakage current. To address this issue, we demonstrated that blending the ionic polymer poly(ethylene oxide) (PEO) with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) not only enhances the conductivity and flexibility of the polymer conductors but also achieves local self-planarization. For the emissive layer, we successfully achieved multicolor LEDs covering the entire visible spectrum on both paper and textile substrates by substituting halide elements in the perovskite material (MAPbX₃) and formulating inks with varying halide compositions. The brightness and efficiency of LEDs were further boosted by introducing the butylammonium (BA) group to reduce the perovskite structure dimensionality to form 2D Ruddlesden−Popper perovskite (RPP) BA₂(MAPbI₃)_n−1PbI₄. Furthermore, systematic investigations on perovskite-polymer composites demonstrated that the morphology and optoelectronic properties of the perovskite photoactive layer can be tuned by incorporating different polymer additives. Specifically, PEO allows for precise and smoother perovskite film deposition by tuning ink rheology and viscosity, while polystyrene (PS) increases the density and uniformity of crystal arrangement, resulting in improved LED brightness and reduced current leakage. Poly(methyl methacrylate) (PMMA) helps reduce grain defects and boundaries in perovskite polycrystalline films, benefiting carrier diffusion in photodetectors.<br/><br/>The PeLEDs written on paper substrates exhibited a brightness as high as 15,225 cd/m², a current efficiency of 6.65 cd/A, and a turn-on voltage of 2.4 V. The PePDs demonstrate an on/off ratio exceeding 10⁴ and a response time of less than 15 ms. Owing to the extraordinary flexibility of each functional layer, the written LEDs on paper substrates could be bent to an extreme curvature radius of 1 mm for over 5000 cycles without performance decay. In summary, the written perovskite optoelectronic devices show great promise for low-cost and large-area emerging applications such as deformable displays, wearable E-textiles, E-papers, and E-packaging.<br/><br/>References:<br/>1. Zhao, Junyi, et al. "Handwriting of perovskite optoelectronic devices on diverse substrates." <i>Nature Photonics</i> 17.11 (2023): 964-971.<br/>2. Zhao, Junyi, et al. "High-Speed Fabrication of All-Inkjet-Printed Organometallic Halide Perovskite Light-Emitting Diodes on Elastic Substrates." <i>Advanced Materials</i> 33.48 (2021): 2102095.