All-Solution-Processed Fabrication of Intrinsically Flexible Multicolor Perovskite Light-Emitting Diodes and Photodetectors on Diverse Substrates (Elastomer, Paper, Textiles, etc.)

Owing to the unique properties such as tunable bandgap and strong optical absorption, perovskite holds great potential for optoelectronic device applications. Although significant progress has been made to explore high-performance light-emitting diodes (LEDs) and photodetectors (PDs) using perovskite, existing fabrication techniques based on the rigid substrate are unable to meet the growing demand from 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 our daily life, including paper, textiles, plastics, rubber, metal, and even three-dimensional surfaces using a versatile and low-cost direct writing approach. Compared to conventional spin-coating and vacuum-evaporation processes, the 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. A significant challenge when implementing optoelectronic devices on paper and textiles is the rough surface morphology of yarn and fiber networks, which can lead to nonuniform film thickness and leakage current. To address this issue, we have demonstrated that blending 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 achieve local self-planarization. For the emissive layer, we have 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. Meanwhile, the brightness and efficiency of LEDs could be further boosted by introducing the butylammonium (BA) group to reduce the perovskite structure dimensionality to form 2D Ruddlesden−Popper perovskite (RPP) structures. Furthermore, we have conducted systematic investigations on perovskite-polymer composites and 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, benefiting carrier diffusion in photodetectors. The PeLEDs written on paper substrates exhibited a brightness as high as 15,225 cd m^-2, a current efficiency of 6.65 cd/A, and a turn-on voltage of 2.4 V. Owing to the extraordinary flexibility of each functional layer, the written LEDs on the paper substrate could be bent to a 1 mm extreme curvature radius for over 5000 cycles without decay in performance. In summary, the written perovskite optoelectronic devices are ideally suited for low-cost and large-area emerging application scenarios such as deformable displays, wearable E-Textiles, E-Papers, and E-packaging.