Direct Handwriting of All-Solution-Processed and Intrinsically Flexible Multicolor Perovskite Light-Emitting Diodes and Photodetectors on Textiles and Papers

Textiles and papers, made of percolation yarn- and fiber- networks, are commonly used in our daily life and they hold great potential to be platforms for next-generation flexible and wearable electronics. In this work, we report a versatile and ultra-fast mask-free fabrication strategy that enables direct handwriting of all-solution-processed halide perovskite optoelectronic devices onto papers, textiles (cotton, polyester, and nylon), and other unconventional substrates including metal foil, plastic film, rubber balloon, vinyl glove, and even 3-dimensional surfaces such as glass vial or spheres. More specifically, we have developed and formulated universal electronic inks that could either be used in printing/coating machines or loaded into ballpoint pens for direct handwriting on target substrates. These electronic inks include poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and poly(ethylene oxide) (PEO) composite ink for transparent anodes, perovskite and polystyrene (PS)/ poly(methyl methacrylate (PMMA) composite ink for the photoactive layer, polyethylenimine (PEI) ink for the electron transporting layer, and silver nanowires ink for semi-transparent cathodes. The PEO component blended in the PEDOT:PSS conducting ink not only helped planarize the rough percolating yarn/fiber substrates, but also improved the conductivity and conformability of conducting film, thus leading to improved device performance and stability. By directly writing the above functional inks onto the substrate layer by layer, we have demonstrated high-performance multicolor light-emitting diodes (LEDs) with emissions covering the entire visible spectrum and photodetectors (PDs) in both a vertical photodiode configuration and a planar photoconductor configuration. The direct-drawn LEDs exhibited a brightness as high as 15,225 cd m^-2 with a turn-on voltage of 2.4 V; and the PDs exhibited an on-off ratio over 10⁴, a responsivity up to 132 mA/W, and a response time of less than 15 ms. Compared with existing microfabrication and printing processes, the direct handwriting approach allows high-performance optoelectronics being easily fabricated by untrained individuals in a time-efficient and cost-effective manner. The formulated inks buffered with handwriting technique are especially meaningful for early-stage demonstration and ideally suited for low-cost and large-area application scenarios such as E-Textiles, E-Packaging, and E-Papers with less stringent requirements on resolution. Additionally, the handwritten LEDs showed extraordinary robustness which could be bent to a 1 mm extreme curvature radius for over 5000 cycles without decay in performance. Overall, such low-cost and eco-friendly textile/paper-based LEDs and PDs could pave way for the integration of optoelectronics with wearable and human-machine interface applications.