Skin-like displays are critical components of information output in next-generation portable and wearable electronics. Currently, all such displays are fabricated on glass or thick plastic substrates, limiting the inherent mechanical flexibility of organic materials and preventing intimate skin contact. Developing active-matrix (AM) displays comprising organic thin-film transistors (OTFTs) and organic light-emitting diodes (OLEDs) is crucial for achieving high-quality skin-like displays. Almost all reported AMOLED displays are parallel structures consisting of side-by-side OTFTs and OLED. Unfortunately, this parallel structure covers part of the pixel area by nonluminous OTFTs and wiring, resulting in low active area, luminance, resolution, and aperture ratio. The vertical structure is more conducive than the parallel structure for fabricating AMOLEDs with a high aperture ratio. Vertically stacking OLEDs and OTFTs eliminates obstruction from nonluminous OTFTs and wiring parts, maximizing the active area. In addition, a vertically structured pixel minimizes the occupied area, dramatically improving the display's resolution and quality. Nevertheless, fabricating vertically structured skin-like AMOLEDs is complex because such displays introduce new challenges, including mutual dissolution, mechanical compatibility, and interconnection between functional layers.
Researchers propose a general strategy of "discrete preparation-multilayer lamination" for the first demonstration of vertically stacked skin-like active-matrix displays. This strategy is mainly to separately prepare each conformable functional layer (OLED/interconnection layer/OTFT), and then laminate them together, which effectively avoid chemical and physical damage and ensure mechanical compatibility and interconnection between functional layers. Researchers experiments introduced no solvents or water during the peeling process, and no additional adhesives were used during the lamination process. This all-dry fabrication avoids mutual dissolution and interface pollution, providing a clean, complete contact interface for fabricating high-quality vertically stacked skin-like displays.
Compared with existing active-matrix display fabrication strategies, the proposed strategy has several advantages: (i) In contrast with the parallel AMOLED preparation strategies, we separately prepared each conformable functional layer (TE-OLED/interconnection layer/all-photolithographic OTFT) and then vertically laminated them together. This strategy significantly improves the aperture ratio. By linking the interconnect layer, the OLED array becomes intimately and vertically stacked on an all-photolithographic OTFT array. The entire array is complete and has no deletions or cracks. The aperture ratio of a pixel is as high as 83%, and the aperture ratio of the display array reaches 71%, both of which surpass the results of all previously reported flexible AMOLED displays. (ii) Unlike conventional layer-by-layer deposition techniques, this strategy eliminates chemical (i.e., various solvents) or physical (i.e., etching and heating) damage to fragile organic materials during fabrication, which is essential for fabricating reproducible, high-quality vertically stacked skin-like displays. In addition, this strategy can integrate modern microelectronic techniques such as photolithography and etching into the skin display, allowing mass production of highly-integrated, high-resolution skin-like displays. (iii) In contrast with the layer-by-layer preparation on rigid or flexible substrates, all functional layers are stripped from rigid substrates, liberating them from any mechanical limitations imposed by these substrates. Thus, the proposed display has outstanding mechanical flexibility and good conformability.
