Counterfeiting poses a significant global threat to economies, health, and the environment. Current anticounterfeiting technologies, primarily relying on photoresponsive materials printed on paper, often have low security thresholds. This research aims to enhance security by integrating optoelectronic devices, specifically organic light-emitting diodes (OLEDs), into paper-based anticounterfeiting. OLEDs offer the advantage of generating both electro-responsive and photo-responsive patterns. However, integrating high-performance OLEDs onto paper substrates presents challenges due to the paper's porous and rough nature, leading to device breakdown or short circuits. This study overcomes these challenges to create a high-performance, flexible, and secure anticounterfeiting device.

The paper reviews existing anticounterfeiting technologies, including dithered patterns, plasma tags, security inks, holograms, watermarks, and long-lag phosphors. These methods, mostly based on photoresponsive materials printed on paper, are noted for their low security threshold. The integration of optoelectronic devices, particularly OLEDs, is proposed as a solution to improve security by adding multiple stimuli responsiveness. The authors highlight the technical challenges of integrating OLEDs onto paper due to the material's properties and morphology, emphasizing the lack of previous reports on high-performance paper-based OLEDs.

The researchers investigated five commercially available papers (stone, art, printing, sulfuric, and filter paper) and chose stone paper for its environmental friendliness. A QR code was printed on the paper, followed by dip-coating with poly(methyl methacrylate) (PMMA) to modify the paper's morphology, filling pores and creating a smoother surface. Atomic force microscopy confirmed the improved surface flatness (roughness of 21.4 nm). A top-emitting OLED structure was then deposited using a shadow mask to create a patterned emitting layer. The device structure consisted of Al/MoO3/TAPC/TcTa/CBP:Ir(ppy)3/TmPyPB/LiF/Mg:Ag/Ag. The performance of the paper-based OLED (TG-P) was compared to a glass-based OLED (TG-G). Mechanical flexibility was tested by bending the device multiple times and measuring its performance. Peel-adhesion tests were conducted to assess the adhesion strength between the Al electrode and the paper substrate compared to a PET substrate. Finally, a flexible anticounterfeiting device was created by integrating patterned electro-responsive and photo-responsive organic emitters onto the treated paper substrate.

The PMMA dip-coating process successfully modified the paper's surface, creating a suitable substrate for OLED fabrication. The resulting paper-based OLED (TG-P) demonstrated comparable brightness and current efficiency to the glass-based OLED (TG-G), achieving a maximum brightness of 71346 cd m⁻² and a maximum current efficiency of 64 cd A⁻¹. Using art paper, even higher values of 110000 cd m⁻² and 90 cd A⁻¹ were obtained. The device exhibited an operating half-lifetime of over 4000 hours at 100 cd m⁻². The paper-based OLED showed excellent mechanical flexibility, maintaining performance after 1000 bending cycles, outperforming a PET-based OLED. The superior flexibility was attributed to the lower flexural modulus and bending strength of the treated paper compared to PET. Stronger adhesion between the Al electrode and the paper substrate was also observed. The FAC device demonstrated multiple unclonable behaviors, showing varying patterns and colors in response to light, electricity, and combined stimuli, along with discernible color shifts depending on viewing angle and voltage.

The results demonstrate the successful integration of high-performance OLEDs onto a paper substrate for anticounterfeiting applications. The use of PMMA dip-coating effectively addressed the challenges posed by the paper's inherent roughness, achieving OLED performance comparable to glass-based devices. The exceptional flexibility of the device, exceeding that of PET-based OLEDs, significantly expands the application possibilities. The multiple stimuli responsiveness of the FAC device creates a highly secure and unclonable anticounterfeiting system, offering a significant advancement in the field.

This research successfully developed a high-performance, flexible, and multifunctional optoelectronic anticounterfeiting device using organic light-emitting paper. The device exhibits superior performance and flexibility compared to existing technologies. Future research could explore different organic materials and device structures to further enhance performance and expand the range of stimuli responsiveness.

While the study demonstrates excellent results, further investigation into long-term stability under various environmental conditions is needed. The scalability of the fabrication process for mass production should also be explored. Finally, a comprehensive security analysis comparing the proposed method to existing techniques would strengthen the overall contribution.