Fully Printed Light‐Emitting Electrochemical Cells Utilizing Biocompatible Materials

Abstract

The use of biomaterials and bioinspired concepts in electronics will enable the fabrication of transient and disposable technologies within areas ranging from smart packaging and advertisement to healthcare applications. In this work, the use of a nonhalogenated biodegradable solid polymer electrolyte based on poly(ε-caprolactone-co-trimethylene carbonate) and tetrabutylammonium bis-oxalato borate in light-emitting electrochemical cells (LECs) is presented. It is shown that the spin-cast devices exhibit current efficiencies of ≈2 cd A −1 with luminance over ≈12 000 cd m −2 , an order of magnitude higher than previous bio-based LECs. By a combination of industrially relevant techniques (i.e., inkjet printing and blade coating), the fabrication of LEC devices on a cellulose-based flexible biodegradable substrate showing lifetimes compatible with transient applications is demonstrated. The presented results have direct implications toward the industrial manufacturing of biomaterialbased light-emitting devices with potential use in future biodegradable/ biocompatible electronics.

Ultrathin Fully Printed Light‐Emitting Electrochemical Cells with Arbitrary Designs on Biocompatible Substrates

“…After the steady state is reached the ion movement is stopped and doped areas in the organic semiconductor are created in the interface to the contacts. [52] For the inkjet-printed PEDOT:PSS a conductivity of 255 S cm −1 was determined with linear four-point measurement which is around one order of magnitude lower than ITO (≈6000 S cm −1 ). [65] The working mechanism of LECs provokes a certain turn-on time because light emission only occurs after the ions have dissociated to a certain extent, however this drawback is equalized by the very simple fabrication process of the technology.…”

“…Between the doped regions a light-emitting p-n-junction is formed in analogy to an inorganic light-emitting diode. [52,68,69] However the current density follows a characteristic profile typical for LECs. [66,67] From the LIV-characteristics (Figure 3a) one can see that the device has a turn-on voltage of 6.7 V and reaches its maximum luminance of 918 cd m −2 at 15 V. The rather high operating voltages compared to similar devices is attributed to the low conductivity of the PEDOT:PSS electrode.…”

“…The lifetime of LECs is commonly measured in constant current mode rather than in constant voltage mode. [47][48][49][50][51][52] Specially, this study reports an operational lifetime on the timescale of several hours for fully printed LECs which would enable its application in disposable applications. In Figure 3c one can see that the LEC can deliver a significant luminance >100 cd m −2 for 8.8 h which is sufficiently long for disposable applications in the fields of advertisement, packaging, or wearable electronics.…”

“…[42,43] For the light generation we are using a light-emitting electrochemical cell (LEC). [47][48][49][50][51][52][53][54] However, no studies are known to the authors in which the device active layer and top and bottom electrodes of the LECs were completely fabricated by scalable printing techniques in addition to exhibiting operational lifetimes of at least several hours. Concerning solution processing this fact simplifies the production in a crucial manner.…”

“…Concerning solution processing this fact simplifies the production in a crucial manner. [52] Except SY this selection of materials is certified for biodegradability and biocompatibility enabling a potential application at biological interfaces. [47][48][49][50][51][52][53][54] However, no studies are known to the authors in which the device active layer and top and bottom electrodes of the LECs were completely fabricated by scalable printing techniques in addition to exhibiting operational lifetimes of at least several hours.…”