Charge carrier traps are discrete states within organic semiconductors with the propensity to capture and hold onto electrons or holes, thereby hindering their contribution to electrical conductivity ...and frequently diminishing device performance. Despite extensive research into charge-trapping mechanisms, the precise origins of these trap states remain elusive. This review endeavours to bridge this knowledge gap by compiling a range of factors identified as instrumental in the genesis of traps. The review commences with an introductory overview of organic semiconductors and a definition of charge carrier traps. Subsequently, we delve into an examination of the myriad origins of trap states and their impact on the function of organic electronic devices culminating with a discussion of various approaches devised to mitigate the effects of charge carrier trapping. This includes an exploration of the potential for harnessing charge carrier traps within the realms of artificial intelligence and neuromorphic computing.
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•Charge traps in OSCs hinder electrical conductivity.•Origins of traps in OSCs are diverse and complex.•Traps affect device performance, reducing efficiency.•Minimizing effect of traps is key for advanced OSC applications.
High mechanical flexibility and wavelength tunability of organic semiconductor materials have propelled the development of organic semiconductor lasers (OSLs) as a complementary technology to current ...inorganic lasers. While excellent progress has been made across multiple aspects of OSLs, demonstration of long‐pulse operation quasi‐continuous wave (qCW) or continuous wave (CW) lasing has presented significant challenges due to the detrimental accumulation of triplets under long‐pulse photoexcitation and substantial quenching of singlet excitons, arising from singlet‐triplet annihilation (STA). In particular, qCW or CW lasing from solution‐processed OSL materials has not been reported, and thus remains a long‐thought objective in optoelectronic research. Using a novel bis(N‐carbazolylstyryl)‐9,9‐dihexylfluorene (BSFCz), the first solution‐processable organic laser dye demonstrating lasing oscillation in the long‐pulse photoexcitation regime (up to 10 ms pulse width) with a low threshold (420 W cm−2), which in part can be attributed to its negligible spectral overlap between triplet excited‐state absorption and laser emission, is herein reported. Temporal emission profiles below and above the lasing threshold also demonstrate that STA has a negligible effect on emission. These combined observations show BSFCz incur low losses due to triplet excited‐states, leading to extremely small changes in lasing thresholds when moving from pulsed to qCW (>1 ms) excitation.
The first lasing activity under long‐pulse (up to 10 ms) photoexcitation from a new solution‐processable organic semiconductor laser dye is demonstrated. Its negligible spectral overlap between triplet excited‐state absorption and emission, coupled with its high molar extinction coefficient, high radiative decay rate, short excited‐state lifetimes, and low solid‐state ASE and lasing thresholds (0.9–1.1 µJ cm−2), enables the long‐pulse lasing.
Engineering semiconductor devices requires an understanding of charge carrier mobility. Typically, mobilities are estimated using Hall effect and electrical resistivity meausrements, which are are ...routinely performed at room temperature and below, in materials with mobilities greater than 1 cm2 V‐1 s‐1. With the availability of combined Seebeck coefficient and electrical resistivity measurement systems, it is now easy to measure the weighted mobility (electron mobility weighted by the density of electronic states). A simple method to calculate the weighted mobility from Seebeck coefficient and electrical resistivity measurements is introduced, which gives good results at room temperature and above, and for mobilities as low as 10−3 cm2 V‐1 s‐1,
μw=331cm2Vs(mΩ cmρ) (T300 K)−3/2 exp |S|kB/e−21+exp−5(|S|kB/e−1) +3π2|S|kB/e1+exp5(|S|kB/e−1) Here, μw is the weighted mobility, ρ is the electrical resistivity measured in mΩ cm, T is the absolute temperature in K, S is the Seebeck coefficient, and kB/e = 86.3 µV K–1. Weighted mobility analysis can elucidate the electronic structure and scattering mechanisms in materials and is particularly helpful in understanding and optimizing thermoelectric systems.
The weighted mobility, easily computed from measurements of the Seebeck coefficient and electrical resistivity, is an accurate measure of the charge carrier mobility and effective mass. It is even more sensitive than measurements of the Hall effect for revealing electron transport mechanisms in complex materials ranging from metals, semiconductors, and conducting polymers.
Compared to inorganic semiconductors and/or fullerene derivatives, nonfullerene n‐type organic semiconductors present some advantages, such as low‐temperature processing, flexibility, and molecule ...structure diversity, and have been widely used in perovskite solar cells (PSCs). In this research news article, the recent advances in nonfullerene n‐type organic semiconductors which function as electron‐transporting, interface‐modifying, additive, and light‐harvesting materials in PSCs are summarized. The remaining challenges and promising future directions of nonfullerene‐based PSCs are also discussed.
Nonfullerene n‐type organic semiconductors possess unique advantages over inorganic semiconductors and/or fullerene derivatives in perovskite solar cells. This research news article summarizes and discusses the recent development of the multifunctional nonfullerene n‐type organic semiconductors used in perovskite solar cells.
The furan–thiophene‐based quinoidal organic semiconductor, TFT‐CN, is designed and synthesized. TFT‐CN displays a high electron mobility of 7.7 cm2 V−1 s−1, two orders of magnitude higher than the ...corresponding thiophene‐based derivative.
The field of organic electronics thrives on the hope of enabling low‐cost, solution‐processed electronic devices with mechanical, optoelectronic, and chemical properties not available from inorganic ...semiconductors. A key to the success of these aspirations is the ability to controllably dope organic semiconductors with high spatial resolution. Here, recent progress in molecular doping of organic semiconductors is summarized, with an emphasis on solution‐processed p‐type doped polymeric semiconductors. Highlighted topics include how solution‐processing techniques can control the distribution, diffusion, and density of dopants within the organic semiconductor, and, in turn, affect the electronic properties of the material. Research in these areas has recently intensified, thanks to advances in chemical synthesis, improved understanding of charged states in organic materials, and a focus on relating fabrication techniques to morphology. Significant disorder in these systems, along with complex interactions between doping and film morphology, is often responsible for charge trapping and low doping efficiency. However, the strong coupling between doping, solubility, and morphology can be harnessed to control crystallinity, create doping gradients, and pattern polymers. These breakthroughs suggest a role for molecular doping not only in device function but also in fabrication—applications beyond those directly analogous to inorganic doping.
Strong interactions between molecular dopants and organic semiconductor morphology are often responsible for charge trapping and low doping efficiency. This study reviews how solution‐processing techniques can control these interactions and render them useful for engineering diffusion rates, doping gradients, and film topography. These breakthroughs suggest new roles for molecular doping in device fabrication as well as function.
The organic electrochemical transistor (OECT) is one of the most versatile building blocks within the bioelectronics device toolbox. While p‐type organic semiconductors have progressed as OECT ...channel materials, only a few n‐type semiconductors have been reported, precluding the development of advanced sensor‐integrated OECT‐based complementary circuits. Herein, green aldol polymerization is uses to synthesize lactone‐based n‐type conjugated polymers. Fluorination of the lactone‐based acceptor endows a fully locked backbone with a low‐lying lowest unoccupied molecular orbital, facilitating efficient ionic‐to‐electronic charge coupling. The resulting polymer has a record‐high n‐type OECT performance with a high product of mobility and capacitance (µC* = 108 F cm−1 V−1 s−1), excellent mobility (0.912 cm2 V−1 s−1), low threshold voltage (0.02 V), and fast switching speed (τON, τOFF = 336 µs,108 µs). This work demonstrates two types of device architectures and applications enabled by the high performance of this n‐type OECT, i.e., an artificial synapse and a complementary amplifier for detecting α‐synuclein, a potential biomarker of Parkinson's disease. This study shows that materials that enable high gain and fast speed n‐type OECTs can be developed via a green polymerization route, and the diverse form factors that these devices take promise for exploration of other application areas.
Fluorinated lactone‐based polymer p(C2F‐V) has a fully locked backbone leading to a record‐high n‐type organic electrochemical transistor performance. This work demonstrates two types of device architectures and applications enabled by this n‐type semiconductor, i.e., an artificial synapse and a complementary amplifier for detecting α‐synuclein, a potential biomarker of Parkinson's disease.
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