Organic Electronics最新文献

In organic solar cells, the absorption range and extinction coefficient of the active layer not only affect the charge separation and carrier transfer efficiency of excitons, but also influence the J_SC, and thus the device efficiency. Herein, an efficient nonfullerene polymer solar cells (NF–PSCs) based on a medium-bandgap (MBG) polymer donor PBDTTS-TClQx comprising chlorinethiophene quinoxaline (Qx) unit and a small molecule nonfullerene acceptor (SM-NFA) Y6 is developed. The PBDTTS-TClQx shows a strong absorption in the wavelength region of 330∼750 nm with an optical band gaps (E_g^opt) of 1.68 eV, which is well complementary with that of Y6 (1.33 eV) and facilitates achieving of high short-circuit current (J_SC) in PSCs. As a result, the PBDTTS-TClQx:Y6-based PSCs achieved a power conversion efficiency (PCE) of 14.28% with a J_SC of 25.9 mA cm⁻². The J_SC of 25.9 mA cm⁻² achieved is among the highest reported for Qx-based polymer donors in PSCs.

The reflection losses are among the principal causes that limiting the performances of the solar cells. Indeed, the conventional organic solar cell (OSC) provides a relatively low photocurrent mainly due to light reflection at the front and back sides of the glass-substrate. To overcome this limitation we propose an optimized hybrid antireflective structure. The proposed design is a combination between multilayer antireflection coating (MARC) and moth eye structure (MES). The OSC with this antireflection coating, consisting of thin coherent multilayer stack and moth eye subwavelength structure, is modeled using transfer matrix method (TMM) and effective medium theory (EMT). In this work, several antireflection coating designs with different dielectric material films are investigated. The layer thicknesses of the MARC were tuned such that they obey to quarter-quarter-quarter (Q-Q-Q) and quarter-half-quarter (Q-H-Q) wavelength rules to obtain zero reflectance. Based on these configurations, we performed an optimization algorithm to design the antireflection coating that maximizes the short circuit photocurrent density (J_SC). The optical analysis is applied to ITO/PEDOT:PSS/P3HT:PCBM/Al bulk heterojunction (BHJ) organic solar cell. The highest value of short circuit photocurrent density is obtained for OSC with hybrid MES/Glass-substrate/MARC(QHQ) antireflective structure using Al₂O₃/ZrO₂/M-optm material films. In comparison with the conventional organic solar cell without antireflection coating, the short circuit photocurrent density was improved by 5% at normal incidence. Besides, the antireflection effect is maintained even at large incidence angle of 68° thanks to the omnidirectional optical propriety of the moth eye structure.

A very promising approach to achieving stable polymer P-N junctions is polymer light-emitting electrochemical cells (LECs). In LECs, under a specific voltage bias, the injection of carriers into the polymer occurs through a redox reaction and subsequently gets compensated by opposite ions, resulting in the creation of electrochemical doping. Unlike organic light-emitting diodes, which have numerous mature electrical current models serving as invaluable tools for understanding the underlying mechanism and predicting device performance, LECs lack such modeling. This lack of modeling stems from the greater complexity of LECs, as the electrical current in LECs is composed of not only electronic components but also ionic contributions, along with a side-reaction portion arising from the electrochemical reaction. This work demonstrates an electrical current model for LECs, which is simple and accurate enough for practical applications. The model achieves a quantitative separation of electronic and ionic charge contributions to the electrical currents, as well as provides insights into the distribution of oxygen through operation schemes. Additionally, this paper incorporates the relationships between oxygen level, voltage, temperature, and current into the current model, thereby discerningly formulating expressions for ionic and electronic currents within the model. This demonstrates a precise equation for LEC electric current.

Pseudo-halide substitution is an effective approach to enhance the performance and stability of perovskite optoelectronic devices. However, the role of pseudo-halide ions played in the perovskite light-emitting diodes (PeLEDs) is still rarely investigated. Herein, we have synthesized the organic salt PEABF₄ (PEA = phenylethylamine) as a pseudo halide substitute for surface halides in PEABr and fabricate quasi two-dimensional (quasi-2D) PeLEDs. The incorporation of BF₄⁻ anion improves the photoluminescence (PL) intensity and lifetime by taking advantage of improved crystallinity and enlarged grain size. The BF₄⁻ substituted PeLEDs shows great improvement of performance to the control devices. The optimized device with structure of indium tin oxide-coated glass (ITO(glass))/poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS)/perovskite/4,7-Diphenyl-1,10-phenanthroline (Bphen)/Ag produces a maximum luminance at 44850 cd/m², and an efficiency of 11.5 cd/A, respectively. Through further investigation by optical and electrical characterization, we find the substitution of BF₄⁻ anion has merits on the enhancement of exciton binding energy and suppression of non-radiative trap-assisted recombination on the surface. These results provide better understanding of pseudo-halide's benefits in perovskite light-emitting devices.

Functional and low-cost switching materials are necessary to sustain the development of data storage and brain-inspired computing technologies. Polypyrrole (PPy) is one of the potential organic polymer materials for resistive switching (RS) applications. Given this, the present work reports the electrochemical synthesis of PPy and gold (Au) decorated PPy (Au-PPy) switching layers for non-volatile memory and neuromorphic computing applications. Among two switching layer materials, the Au decorated PPy (Ag/Au-PPy/Pt) shows good bipolar RS properties in terms of cyclic stability (16,000 cycles), memory retention (6000 s), and memory window (>60). Moreover, Ag/Au-PPy/Pt device realistically mimic the various bio-synaptic properties such as potentiation, depression, excitatory post-synaptic current (EPSC), and paired-pulse facilitation (PPF) index (%) as compared to Ag/PPy/Pt device. The double-valued charge-flux relation asserted that both devices are non-ideal memristors. Various statistical techniques such as cumulative probability, Weibull distribution, and time series analysis techniques were utilized to understand, model, and predict the switching variation of both devices. Moreover, the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were probed to understand the RS process of the devices. The conduction and plausible RS mechanisms of the optimized device were also reported. The results of the present work assert that the Au-decorated PPy is a potential organic polymer material for data storage and neuromorphic computing applications.

Supercapacitors using the electrolyte containing aniline-substituted viologen were fabricated, and the effects of the substitution number of the aniline group on viologen materials were studied. The electrolyte mainly comprised 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide, dimethyl ferrocene, and the aniline-substituted viologens. As-synthesized aniline monomer, aniline dimer, and aniline trimer were used to substitute into the nitrogen site of the viologen molecule. The areal capacitance value of aniline dimer substituted viologen was 5.81 mF/cm², while the values for aniline monomer and aniline trimer substituted viologens were 0.82 and 2.17 mF/cm², respectively. The electrochemical stability for 1000 cycles was 98.6%, 90.8%, and 20.3% for the aniline monomer, aniline dimer, and aniline trimer substituted viologens, respectively. Electrolytes with aniline dimer substituted viologen represented good performance and high stability. On the other hand, aniline monomer exhibited poor performance for the supercapacitor, and aniline trimer substituted viologen showed very low stability, originating from a low solubility to build electrolytes. From these results, the aniline dimer was the appropriate substituent for the viologen, and the proposed material is expected to play an important role in enhancing the performance of the organic supercapacitor.

The crystalline and amorphous phases often coexist in the organic active layers of their electronic devices, which further undergo morphological changes over time. Understanding of the characteristics of the microscopic processes in polycrystalline organic films is essential for optimizing organic semiconductors and their devices, particularly in the context of flexible electronics. Here, we systematically investigate the charge-carrier distributions and transport in polycrystalline organic films, focusing on the impact of the crystallinity and grain density. These polycrystalline morphology data were generated from an efficient Monte Carlo method, which were then incorporated into molecular-level device simulations that can describe the microscopic charge-transport processes. These results demonstrate the distributions and transport characteristics of charge carriers in different phases of the polycrystalline organic semiconductor films, as well as the influencing factors. Importantly, we show that the influence of a polycrystalline morphology becomes more pronounced at low driving voltages, which has been the subject of significant research efforts. Our study also revealed a decrease in mobility at low crystallinities, a phenomenon that was not previously anticipated.

In addition to emission efficiency and colors, emission characteristics such as preferentially horizontal emitting dipole orientation and resistance against concentration quenching are also highly desired for high-performance thermally activated delayed fluorescence (TADF) emitters. In this work, we report a simple and yet effective strategy for enhancing such emission performance of the pure red-to-near infrared (NIR) TADF emitter by introducing bulky aryl derivatives (m-xylene) to the efficient emission core. Incorporating m-xylene groups as the electronically inert pendants to the acceptor unit of the TADF emitter TPA–CN–N4-CH3 successfully retains favorable emission properties (e.g., pure red color chromaticity, nearly unitary photoluminescence quantum yield etc.) of the parent compound TPA–CN–N4 and yet also renders significantly higher horizontal emitting dipole ratio Θ// of ∼85 % with the more extended molecular configuration and reduced concentration quenching at very high concentrations in thin films. As a result, OLEDs adopting TPA–CN–N4-CH3 can demonstrate rather high EQEs of 29.8–32.1 % for pure red emission (625–650 nm) at low doping concentrations and decent EQEs of 18.9–27.5 % in the deep red to NIR range (650–700 nm) at higher doping concentrations. The results of this work shall provide a useful reference for development of efficient TADF emitters.