Stretchable inkjet-printed electronics on mechanically compliant island-bridge architectures covalently bonded to elastomeric substrates

Herein, we present an approach that allows versatile combination of inkjet-printed electronics and stretchable substrates. For this, we created a hybrid platform made out of stretchable Ecoflex covalently bonded via silane monolayers to flexible polyethylene terephthalate islands interconnected by bridges. The islands served as platforms where conductive lines, capacitive sensors and electrochromic devices (ECDs) were fabricated by inkjet printing. The robustness of the approach is highlighted by the minor influence of strain on the conductivity of printed Ag electrodes, which changed the resistance only by 1.3% at an applied strain of 50%. Furthermore, we demonstrated capacitor sensors capable of responding to strain changing their capacitance from 0.2 to 1.6 pF. To further show the applicability of the approach for multilayer/multimaterial optoelectronic elements, we processed ECDs capable of displaying information on the stretchable platform. Thus, we demonstrate how this digital and additive concept can be applied for the scalable integration of printed optoelectronic devices onto stretchable systems without relying on lithographic processes

Organic photodiodes: printing, coating, benchmarks, and applications

Organic photodiodes (OPDs) are set to enhance traditional optical detection technologies and open new fields of applications, through the addition of functionalities such as wavelength tunability, mechanical flexibility, light-weight or transparency. This, in combination with printing and coating technology will contribute to the development of cost-effective production methods for optical detection systems. In this review, we compile the current progress in the development of OPDs fabricated with the help of industrial relevant coating and printing techniques. We review their working principle and their figures-of-merit (FOM) highlighting the top device performances through a comparison of material systems and processing approaches. We place particular emphasis in discussing methodologies, processing steps and architectural design that lead to improved FOM. Finally, we survey the current applications of OPDs in which printing technology have enabled technological developments while discussing future trends and needs for improvement

Biodegradable inkjet-printed electrochromic display for sustainable short-lifecycle electronics

The fabrication of electronics on the basis of biofriendly materials aims to counterbalance the negative trends conveyed by the short life-cycle of electronics. Furthermore, these materials open the possibility to develop optoelectronic technologies which will be in contact with the human body. In this work, we present an electrochromic display fabricated by resource- and energy-efficient digital printing techniques. The biodegradation of the device is certified under the ISO 14855 standard. The display comprises of a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrochromic layer, a gelatin-based electrolyte and Au electrodes deposited on a cellulose di-acetate substrate. We investigate the impact of various naturally sourced ionic species on the ionic conductivity of the electrolyte and the figures of merit of the display. The printed devices show an electrochromic contrast of 32 ± 4% and switching times of 3.0 ± 1.4 s, comparable to the spincoated reference devices. The utilization of inkjet printing enables the fabrication of different device designs with individually addressable pixels. The display can be worn innocuously on the skin without loss of performance thanks to the self-adhesion properties of the gelatin hydrogel. The present work highlights the use of industrial relevant technology for the fabrication of truly ecofriendly optoelectronic systems

Gas-assisted blade-coating of organic semiconductors: molecular assembly, device fabrication and complex thin-film structuring

The competitive performance of optoelectronic devices based on advanced organic semiconductors increasingly calls for suitably scalable processing schemes to capitalise on their application potential. With performance benchmarks typically established by spin-coating fabrication, doctor-blade deposition represents a widely available roll-to-roll-compatible means for the preparation of large-area samples and establishing the device upscaling potential. However, the inherently slower film formation kinetics often result in unfavourable active layer microstructures, requiring empirical and material-inefficient optimisation of solutions to reach the performance of spin-coated devices. Here we present a versatile approach to achieving performance parity for spin- and blade-coated devices using in situ gas-assisted drying enabled by a modular 3D-printed attachment. This is illustrated for organic photodetectors (OPDs) featuring bulk heterojunction active layers comprising blends of P3HT and PM6 polymer donors with the nonfullerene acceptor ITIC. Compared to conventionally blade-coated devices, mild drying gas pressures of 0.5–2 bar yield up to a 10-fold enhancement of specific detectivity by maximising external quantum efficiency and suppressing dark-current. Furthermore, controlling gas flux distribution enables one-step fabrication of 1D chain conformation and 2D chain orientation patterns in, respectively, PFO and P3HT:N2200 blend films, opening the possibility for high-throughput fabrication of devices with complex structured active layers

Blue-emission tuning of perovskite light-emitting diodes with a simple TPBi surface treatment

We demonstrate a simple approach for blue-emission tuning of quasi-2D perovskite light-emitting diodes through a surface treatment of 2,2′,2″-(1,3,5-benzinetriyl)tris(1-phenyl-1H-benzimidazole) (TPBi). By increasing the TPBi concentration, we achieved tunable electroluminescence of the perovskite layer with wavelength shifted from the blue-green (506 nm) to blue (481 nm) regions of the visible spectrum. Fourier-transform infrared spectroscopy, scanning electron microscopy, and UV–Vis absorption spectroscopy were conducted to study the morphological and optoelectronic properties of the films. Our results suggest that the TPBi molecules accumulated on the surface and grain boundaries of the perovskite layer changed the perovskite electronic structure causing the observed blue shifts

Aerosol‐Jet‐Printed Donor‐Blocking Layer for Organic Photodiodes

Organic photodiodes (OPDs) are optical sensors combining high performance, lightweight mechanical flexibility, and processability from solution. Their fabrication by industrial printing techniques opens a wide range of innovative applications for emerging fields in sensing and the Internet of Things. They typically consist of printed multilayers with functionalities to absorb light, to extract charges, or to reduce detection noise. However, the printing of such device architecture poses a challenge as the deposition of a material can lead to disruption of film morphology or intermixing of materials if its solvent interacts with the previously deposited layer. This work proposes a process to print multilayers from the same solvent system utilizing the aerosol-jet technique. By fine adjustment of the aerosol properties through the tube temperature (TTube), the drying time of poly(3-hexylthiophene-2,5-diyl) (P3HT) printed layers is significantly reduced. This allows its deposition onto a P3HT-based bulk-heterojunction (BHJ) without negatively affecting its performance. The additional printed P3HT layer, spatially extends the donor region of the BHJ, providing ideal hole extraction and simultaneous noise reduction by the blocking of injected electrons. This donor blocking layer (DBL) yields a noise reduction of two orders of magnitude in OPDs operated under −2 V reverse bias

Improved performance of perovskite light-emitting diodes with a NaCl doped PEDOT:PSS hole transport layer

We demonstrate a simple and effective way to enhance the performance of perovskite light-emitting diodes (PeLEDs) by utilizing an alkali halide doped PEDOT:PSS as the hole transport layer (HTL). The alkali halide (NaCl) doping helped the growth of the quasi-2D perovskite phases on top of the PEDOT:PSS, it also significantly reduced the exciton quenching in PEDOT:PSS based PeLEDs. More importantly, the doping reduced the work function of the PEDOT:PSS surface, which appropriately modulated the hole injection leading to improved charge balance. This helps to control the recombination zone inside the thin perovskite emitting layer (∼10 nm). The optimized blue-green PeLEDs with the NaCl doped PEDOT:PSS HTL showed a maximum luminance of 1487 cd m$^{-2}$, current efficiency of 2.16 cd A$^{-1}$ with a low turn-on voltage of 3.0 V, which are 217% and 567% higher than the PeLEDs with the pristine PEDOT:PSS layer (turn-on voltage: 3.3 V), respectively

A Single‐Step Hot Embossing Process for Integration of Microlens Arrays in Biodegradable Substrates for Improved Light Extraction of Light‐Emitting Devices

Integration of light management solutions relying on biodegradable materials in organic light‐emitting devices could assist the development of sustainable light sources or conformable and wearable display technology. Using industrially relevant processing techniques, it is shown that microlens arrays can be seamlessly integrated into flexible and biodegradable cellulose diacetate substrates to facilitate extraction of the trapped substrate modes in light‐emitting electrochemical cells. The substrates are patterned for light extraction and optimized for scalable printing processes in a single step by thermally embossing microlenses with polydimethylsiloxane molds on one substrate surface and simultaneous flattening of the other. Furthermore, by implementing the biopolymer substrate with microlens arrays, the total volume fraction of biodegradable materials in the microlense equipped device is 99.94%. The embossed microstructures on the biopolymer substrates are investigated by means of scanning electron microscopy and the angular light extraction profile of the devices is measured and compared to ray tracing simulations. Light‐emitting electrochemical cells with integrated microlens array substrates achieve an efficiency enhancement factor of 1.45, exceeding conventional organic light‐emitting diodes on glass substrates with laminated microlens arrays (enhancement factor of 1.23)