## Introduction

Wearable electronic textiles (e-textiles) have been of great interest owing to their many compelling applications, such as healthcare monitoring/therapy systems, portable energy harvesting devices, and functional outdoor clothes/accessories1,2,3,4. One alluring format of e-textile devices is the e-textile displays that can visually deliver communication information and also provide a high degree of aesthetic design freedom5,6,7,8. As a fundamental building block for such e-textile displays, self-emissive lighting fibers were demonstrated at the early stage by exploiting various existing flexible lighting technologies, including electroluminescent units8,9,10, electrochemical cells11,12, electrochromic devices13,14, and light-emitting diodes15,16,17,18,19,20,21. Among these various lighting fibers, organic light-emitting diode (OLED) fibers have shown impressive progress by achieving high-class electroluminescence (EL) performance with low operating voltages19,20,21,22. Over the simple formation of planar OLEDs on textile substrates23,24,25, OLED fiber configurations could be created through vacuum19 or solution20,21,22 processes available with one-dimensional fiber substrates. In particular, with fiber-to-fiber interconnectable pixel configurations (i.e., separately defined outer pixel contacts), 2-dimensional matrix interconnections for the pixel addressing have been attained from instant contacts between the perpendicularly interlaced OLED fibers and conductive addressing fibers19,21, leading to actual display textiles over lighting textiles.

Despite the technical advances, the current level of OLED fiber technology is still rather in the immature stage due to challenging hurdles. For instance, a portion of the non-emitting area over the available textile area is considerably large due to the nature of interlacing networks in which OLED emitting fibers are alternately obscured by orthogonally placed non-emitting addressing fibers19,21. This results in limited resolution and, therefore, image quality. In addition, the well-developed thin-film encapsulations (TFEs) with hardly-patternable dense dielectric (e.g., metal oxide) barriers26,27,28,29,30,31 formed by atomic layer deposition (ALD) or chemical vapor deposition (CVD) cannot be directly applied to the interconnectable OLED fibers due to the concern of the pixel contact off arising from insulating the exposed pixel contact pads. The lack of high-grade barrier encapsulations is a critical challenge to reaching a practically applicable level of e-textile OLED displays in consideration of their serious vulnerability to the permeation of oxygen or moisture.

To address these issues of the emission area reduction by non-emitting fibers and the underdeveloped encapsulation systems for interconnectable OLED fibers, here we suggest strategic solution options for large emitting-area, highly durable OLED textile displays by applying (i) the addressable network only with integrated OLED emitting fibers and (ii) tailored TFE designs to interconnectable fiber configurations. To enable the matrix addressability without non-emitting addressing fibers, a phosphorescent OLED pixel array is assembled on a half-side of a rectangular strip fiber, while an independent conductor is formed on the opposite fiber side for supplying the electrical power to OLED pixels of interlaced fibers. Unlike the typical TFEs composed of oxide/polymer multilayer18,27,28,29,30, metal/ultrathin (~5 nm) oxide/polymer multilayer TFE is employed as a top encapsulation system for the OLED fiber pixels with exposed contact pads. This multilayer TFE features (i) high permeation barrier property that secures reliable OLED operations even in the water and (ii) controllable conductive domains that offer electrical circumventing paths between pixels and outer contact pads without the oxide patterning. Detailed device designs, fabrication processes, and experimental characterizations, together with proof-of-concept device demonstrations, systematically support the feasibility of the proposed approaches to full emitting-area water-resistant fibrous OLED e-textile displays.

## Results

### Design and fabrication of encapsulated OLED fiber displays

Figure 1a, b schematically illustrate a proposed device design of OLED fiber display and its fabrication procedures. The device is created only with perpendicularly interlaced, encapsulated interconnectable OLED fibers integrated with data-addressing conductors. A half-side of a single OLED fiber consists of a 1-dimensional array of bottom-emission OLED pixels that share a common conductor connected to their anodes but possess individual contact pads linked to their own cathodes over the top encapsulation. On the other hand, the opposite half-side is utilized to span a separate electrical channel with an emission-aperture-defined conductor involved in the pixel addressing from instant contacts with OLED pixel pads on interlaced other fibers. Because every cross-spots of the woven network with these OLED fibers implement physical contact between the OLED pixel pad and the orthogonal addressing conductor, they all can participate in the light emission, meaning that the light dead spots appearing in the previously reported woven textile displays with non-emitting conductive fibers17,19 can be eliminated. The woven textile format with all emitting fibers is advantageous for increasing the emission area fraction against the available textile area compared to that with emitting/non-emitting fibers even at various fiber widths and gaps, which is discussed in detail in the Supplementary Information (Supplementary Notes, Supplementary Fig. 1~3).

The device fabrication began with the formation of the encapsulated OLED pixel arrays on fibers. Colorless polyimide (PI) strips with a rectangular cross-section (2 × 0.15 mm2) were used as base fibers due to their clear division definition (i.e., the OLED pixel array on the front side and the addressing conductor on the rear side) as well as straightforward process handling19,32. The front side of as-prepared PI fibers was covered with a transparent multibarrier of 2-dyadic aluminum oxide (Al2O3, 30 nm)/parylene-C (500 nm)28,29 by ALD and CVD, respectively, for the high-performance bottom encapsulation (water vapor transmission rate; WVTR = ~6 × 10−5 g m−2 day−1). After deposition of the common conductor with a combination of indium tin oxide (ITO, 150 nm, conductivity; σ = ~104 S cm−1) anode and chromium (Cr, 30 nm, σ = ~105 S cm−1) conductive protector on this bottom TFE, a parylene-C separator (1 μm) with periodic apertures (area = 1.5 × 1.5 mm2, period = 6 mm) was produced through CVD and subsequent photolithographic dry etching for the OLED pixel definition. On the ITO anode exposed after wet-chemical etching of the Cr protector in these separator apertures, constituent layers of bottom-emission phosphorescent green OLEDs were thermally deposited, thereby creating a highly efficient but incompletely encapsulated OLED pixel array. Although given colored OLEDs were exploited herein for a proof of concept, other types of bottom-emission small-molecule OLEDs with different colors and materials combinations can be employed without any technical issues because of their similar deposition processes.

The fabrication of the encapsulated interconnectable OLED fibers was completed after the formation of the Cr (30 nm)/silver (Ag, 500 nm) addressing conductor on the rear fiber side for pixel driving by using thermal evaporation with an aperture-defined shadow mask. Figure 1c exhibits a representative photograph of the resulting OLED fiber, where the OLED pixels with upper contact pads can emit the light through the apertures existing in the bottom addressing conductor. Interlacing horizontal and vertical arrays of these OLED fibers (denoted as x-fibers and y-fibers) under the fiber-to-fiber contact layout resulted in a woven fiber matrix with the OLED pixels appearing at every cross-spots (Fig. 1d). As shown in Fig. 1e, a fabricated prototype of the woven fiber display consisting of 10 × 10 OLED fibers was successfully driven via the passive matrix scheme, in which the ITO/Cr common conductors on the front fiber sides and the Cr/Ag addressing conductors on the rear fiber sides were used as the data-lines and the scan-lines in the addressing process, respectively. More details of overall device fabrication procedures are available in the Supplementary Information (Supplementary Methods, Supplementary Fig. 4).

### Electroluminescence performance of OLED fibers

The EL characteristics of the proposed OLED fibers were experimentally examined to manifest the attainability of high-performance lighting fibers. Figure 2a depicts the tested OLED fiber pixel structure composed of ITO (150 nm) anode, 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN, 5 nm) hole injection layer, 4,4’-cyclohexylidenebis[N,N-bis(4-methylphenyl) benzenamine] (TAPC, 40 nm) hole transport layer, tris(4-carbazoyl-9-ylphenyl)amine:bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (TCTA:Ir(ppy)2(acac), 8 wt%, 25 nm) emitting layer, 4,6-bis(3,5-di(pyridine-3-yl)phenyl)-2-methylpyrimidine (B3PYMPM, 35 nm) electron transport layer, 8-hydroxyquinolinolato-lithium (Liq, 1 nm) electron injection layer, and Al (100 nm) cathode, which is an efficient phosphorescent green OLED confirmed on a PI plate (Supplementary Fig. 5). The representative current density (J)-voltage (V)-luminance (L) curves of the TFE-passivated (i.e., fully encapsulated) OLED fiber pixels, measured with the perpendicularly placed Cr/Ag conductive fiber (Fig. 2b), are presented in Fig. 2c, where those of the TFE-less OLED fiber pixels (i.e., only with the domed PU barrier and Al base/contact pads) are also displayed to clarify the performance variation evoked from the introduced TFEs. The TFE-passivated OLED pixels could be turned on at a low voltage level of ~2.3 V once the antifuse in the top TFE was activated. Since their luminance rapidly rose to a reasonably high level as increasing the applied voltage (~2400 cd m−2 at 4.9 V), the high brightness could be achieved as in the OLED plate devices. Compared with the TFE-less OLED pixels (~3400 cd m−2 at 4.9 V), diminished luminance was observed at the TFE-passivated OLED pixels. This resulted from increased series resistance arising from the inserted antifuse in the top TFE (~12 and ~17 mA cm−2 at 4.9 V for the TFE-passivated and TFE-less pixels, respectively), not from any materials degradations during the TFE formation, as supported by their similar levels in the current efficiency (ηc = ~35 cd A−1) and the power efficiency (ηp = ~40 lm W−1) (Fig. 2d). It needs to be mentioned that the relatively severe roll-off behavior of the TFE-passivated OLED pixels at high luminance values seems to be attributed to the suppressed heat dissipation property provoked by thermally insulating TFE sublayers36,37,38.

### Electrical properties of OLED fibers and driving characteristics of their textiles

To avert unexpected device damage at the first operation of as-fabricated OLED fibers with TFEs, the antifuse in the top TFE has to be activated at a moderately low voltage level that does not suddenly yield the intensified current over the device. For designing such low-voltage TFE antifuses, we preferentially measured VBD levels of the antifuse samples consisting of Al/Al2O3/Al multistack with a fixed Al2O3 thickness of 5 nm, as shown in Fig. 3a. As the number of Al2O3 layers increased from 1 (i.e., Al/Al2O3/Al) to 3 (i.e., Al/Al2O3/Al/Al2O3/Al/Al2O3/Al), the VBD monotonically escalated from ~4.9 to ~10.2 V due to the electrical connection of the antifuse in series. Although multiple Al2O3 layers in the antifuse and thus multiple triadic barriers in the TFE can facilitate the permeation blocking property, their increased VBD was apparently unfavorable to the device reliability. This observation means an empirical compromise needs to be involved in determining the Al2O3 layer number of the TFE antifuse: The double Al2O3 layers (i.e., Al/Al2O3/Al/Al2O3/Al) with a VBD of ~7.3 V sounds reasonably acceptable in consideration of the EL parameters (~12,000 cd m−2, ~150 mA cm−2) of OLEDs in this voltage range. The OLED fibers passivated with the 2 triads multibarrier TFE can be safely stabilized after several voltage sweeps for the aging of the initiated antifuse, as indicated in Fig. 3b.

To explicate the driving characteristics of woven OLED fiber displays, Fig. 3c provides a schematic illustration of 8 × 8 OLED fiber arrays operated by the passive matrix addressing scheme. Here, the data-lines (ITO/Cr common conductors) and the scan-lines (Cr/Ag addressing conductors) of 8 x-fibers are denoted as dx1 ~ dx8 and sx1 ~ sx8, and those of 8 y-fibers are dy1 ~ dy8 and sy1 ~ sy8. As pixels on the x-fiber data-lines are linked to the y-fiber scan-lines, and likewise, pixels on the y-fiber data-lines are linked to the x-fiber scan-lines, the addressing for all cross-spot pixels is feasible in this woven fiber matrix. The fiber interconnections can be organized into four distinguishable data-lines/scan-lines combinations: odd-data/odd-scan and even-data/even-scan combinations for the x-fiber pixels (i.e., (dx1, dx3, dx5, dx5)/(sy1, sy3, sy5, sy7) and (dx2, dx4, dx6, dx8)/(sy2, sy4, sy6, sy8)) and odd-data/even-scan and even-data/odd-scan combinations for the y-fiber pixels (i.e., (dy1, dy3, dy5, dy5)/(sx2, sx4, sx6, sx8) and (dy2, dy4, dy6, dy8)/(sx1, sx3, sx5, sx7)). This implies that pixels selected from the different interconnection combinations can be controlled individually in the addressing process. For instance, 4 pixels at (3, 3), (4, 4), (4, 5), and (5, 6) cross-spots in the given illustration of Fig. 3c are simultaneously turned on by activated switch pairs of dx3/sy3, dx4/sy4, dy5/sx4, and dy6/sx5. By applying the passive matrix addressing scheme described above, an instance image representing ‘sprout’ could be successfully displayed on the experimental textile sample, as shown in the photograph in Fig. 3d.

## Discussion

In summary, we demonstrated high-performance fibrous OLED textile displays that featured a large emission area and water resistance exceeding the reported textile devices. A matrix-addressable woven textile format consisting only of integrated interconnectable OLED fibers was implemented to substantiate the large emission area textiles. We designed decoupled fiber domains for a 1-dimensional array of phosphorescence OLED pixels with exclusive contacts and independent addressing conductor involved in the operation of interlaced other fibers. The long-term device durability was enabled by tailoring the encapsulation system to interconnectable OLED fiber pixels. In particular, the devised top TFE of 2-triadic Al/ultrathin Al2O3/parylene-C multilayer allowed not only the achievement of high permeation barrier property but also the construction of low-voltage dielectric antifuses that offered electrical circumventing channels between pixels and outer contact pads. The high EL performance and reliable bending stability of the OLED fibers were also successfully manifested, and the proof-of-concept textiles of these fibers could be operated even in water through the passive matrix driving method tamed to the fiber network.

The device design concepts and fabrication strategies suggested in this study are readily applicable to related advanced classes of fibrous textile displays in several aspects. The scheme of defining decoupled fiber domains can be employed for single fiber integration of various lighting elements with addressing conductors for textile displays without addressing fibers (as in this work) or with other functional electronic elements/devices (e.g., sensors, energy harvesters) for multifunctional (or self-powered) textile displays. The presented passive matrix addressing for interlaced fiber networks may lead the device driving scheme in the early stage of fibrous textile displays before moving toward the active matrix textiles. The high-grade fiber TFEs with antifuses for interconnectable pixels and their wet-chemical-less fabrication process can be an up-and-coming solution for many vulnerable lighting fiber candidates (e.g., perovskite LEDs, polymer LEDs, quantum-dot LEDs) for being long-term stable fibrous textile displays.

## Methods

### Fabrication of OLED fiber textiles

$${{{\mathrm{WVTR}}}} = - n\frac{{M{}_{{{{\mathrm{H}}}}_{{{\mathrm{2}}}}{{{\mathrm{O}}}}}}}{{M{}_{{{{\mathrm{Ca}}}}}}}\delta _{{{{\mathrm{Ca}}}}}\rho _{{{{\mathrm{Ca}}}}}\frac{L}{W}\frac{{dG}}{{dt}},$$