Ecological Biosubstrates Obtained from Onion Pulp (Allium cepa L.) for Flexible Organic Light-Emitting Diodes

Abstract

A new biopolymer obtained from onion pulp (Allium cepa L.) was employed to produce a sustainable substrate for flexible organic light-emitting diodes (FOLEDs). Indium tin oxide (ITO) and SiO2 thin films were deposited by rf-magnetron sputtering onto these biosubstrates to obtain flexible, transparent, and conductive anodes, on top of which FOLEDs were produced. This new biomaterial exhibits an optical transparency of 63% at 550 nm. ITO films were optimized by varying rf power during deposition onto the biopolymers, and their electrical properties are comparable to the those of ITO grown on top of rigid substrates: a carrier concentration of −3.63 × 1021 cm–3 and carrier mobility of 7.72 cm2 V–1 s–1 for the optimized film. Consequently, the sheet resistance and resistivity of this ITO film were 8.92 Ω sq–1 and 2.23 × 10–4 Ω cm, respectively, hence allowing the production of FOLEDs. The A. cepa L. based FOLED was fabricated using CuPc, β-NPB, and Alq3 as organic layers, and it exhibited a maximum luminance of about 2062 cd m–2 at 16.6 V. The current efficiency reached a maximum value of 2.1 cd A–1 at 85.3 mA cm–2. The obtained results suggest the possibility to use these substrates for innovative biocompatible applications in optoelectronics, such as photodynamic therapy.

Development of Conformable Substrates for OLEDs Using Highly Transparent Bacterial Cellulose Modified with Recycled Polystyrene

“…As expected, the glass/ITO‐based OLED exhibits the highest performance, similar to the values reported previously. [ 6,8,23 ] However, the results of this study indicate that BC‐PS as a substrate is comparable to standard glass. All the devices exhibited a turn on voltage of ≈3.0 V for an operation voltage of up to 10 V. The device efficiency and power density of the BC‐PS membrane based OLED were ≈5 cd A −1 at 16 000 cd m −2 and 2.6 mW cm −2 at 10 V, respectively.…”

“…The main bands at 3340, 1016, and 555 cm −1 that are characteristic of BC were not observed, indicating that a PS film formed on the BC surface and the physicochemical properties of the BC, which is consistent with the enhanced hydrophobicity of the BC‐PS observed in the contact angle measurements. [ 23,37–40 ]…”

“…An approach to improve the transparency, which is a requirement for OLED substrates, is to fill the BC interstices with polymers having similar refractive indices (η > 1.5). [ 22 ] To this end, several polymers, such as polyurethane, polycaprolactone, chitosan, poly(3‐hydroxybutyrate), poly(vinyl alcohol), and boehmite‐epoxy siloxane have been employed, [ 2,23,24 ] prepared using different techniques, such as doctor blade deposition, solvent exchange process, immersion, and inkjet printing. [ 20,25 ] However, these methods are not always economically feasible, scalable, simple, fast, and acceptable under a green chemistry approach.…”

The Food–Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri‐Food Residues

“…In this context, a green and ecological biosubstrate fabricated with onion pulp ( Allium cepa L.) was employed to develop flexible organic light‐emitting diodes (FOLEDs). [ 560 ] For this purpose, the onion substrates were produced using a simple, rapid, and highly reproducible solvent casting method (see Section 5). Indium tin oxide (ITO) and SiO 2 thin films were deposited onto the onion‐based biosubstrates to obtain conductive, yet flexible, transparent anodes, on top of which FOLED was produced, as schematically illustrated in Figure 12 c 1 .…”

“…Copyright 2019, Elsevier B.V). c-c 1 ) Flexible organic light-emitting diode (FOLED) fabricated by solvent casting on top of an onion substrate and its c 2 ) current density as a function of applied voltage in the flat and folded states (Adapted with permission [560]. Copyright 2019, American Chemical Society).…”