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Molecular doping plays an important role in controlling the carrier concentration of organic semiconductors. However, the introduction of dopant counterions often results in increased energetic disorder and traps due to the molecular packing disruption and Coulomb potential wells. To date, no general strategy has been proposed to reduce the counterion-induced structural and energetic disorder. Here, we demonstrate the critical role of non-covalent interactions (NCIs) between counterions and polymers. Employing a computer-aided approach, we identified the optimal counterions and discovered that NCIs determine their docking positions, which significantly affect the counterion-induced energetic disorder. With the optimal counterions, we successfully reduced the energetic disorder to levels even lower than that of the undoped polymer. As a result, we achieved a high n-doped electrical conductivity of over 200 S cm−1 and an eight-fold increase in the thermoelectric power factor. We found that the NCIs have substantial effects on doping efficiency, polymer backbone planarity, and Coulomb potential landscape. Our work not only provides a general strategy for identifying the most suitable counterions but also deepens our understanding of the counterion effects on doped polymeric semiconductors. Xiong et al. demonstrate the effects of non-covalent interactions between counterions and n-doped polymers on charge transport properties. They propose an approach, namely "counterion docking", for selecting optimal counterions in doping of organic semiconductors. [ABSTRACT FROM AUTHOR]

Non-fullerene based organic solar cells display a high initial power conversion efficiency but continue to suffer from poor thermal stability, especially in case of devices with thick active layers. Mixing of five structurally similar acceptors with similar electron affinities, and blending with a donor polymer is explored, yielding devices with a power conversion efficiency of up to 17.6%. The hexanary device performance is unaffected by thermal annealing of the bulk-heterojunction active layer for at least 23 days at 130 °C in the dark and an inert atmosphere. Moreover, hexanary blends offer a high degree of thermal stability for an active layer thickness of up to 390 nm, which is advantageous for high-throughput processing of organic solar cells. Here, a generic strategy based on multi-component acceptor mixtures is presented that permits to considerably improve the thermal stability of non-fullerene based devices and thus paves the way for large-area organic solar cells. Non-fullerene-based organic solar cells generally suffer from poor thermal stability and especially in case of devices with thick active layers. Here, the authors report hexanary blends based on multi-component acceptor mixtures with a device efficiency of 17.6% and thermally stability for 23 days at 130 °C. [ABSTRACT FROM AUTHOR]

A critical bottleneck for improving the performance of organic solar cells (OSC) is minimising non-radiative losses in the interfacial charge-transfer (CT) state via the formation of hybrid energetic states. This requires small energetic offsets often detrimental for high external quantum efficiency (EQE). Here, we obtain OSC with both non-radiative voltage losses (0.24 V) and photocurrent losses (EQE > 80%) simultaneously minimised. The interfacial CT states separate into free carriers with ≈40-ps time constant. We combine device and spectroscopic data to model the thermodynamics of charge separation and extraction, revealing that the relatively high performance of the devices arises from an optimal adjustment of the CT state energy, which determines how the available overall driving force is efficiently used to maximize both exciton splitting and charge separation. The model proposed is universal for donor:acceptor (D:A) with low driving forces and predicts which D:A will benefit from a morphology optimization for highly efficient OSC. Understanding the mechanism of non-radiative losses in organic photovoltaics is crucial to improve the performance further. Here, the authors use combined device and spectroscopic data to reveal universal model to maximise exciton splitting and charge separation by adjusting the energy of charge transfer state. [ABSTRACT FROM AUTHOR]

Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells. [ABSTRACT FROM AUTHOR]

The 'phonon-glass electron-crystal' concept has triggered most of the progress that has been achieved in inorganic thermoelectrics in the past two decades. Organic thermoelectric materials, unlike their inorganic counterparts, exhibit molecular diversity, flexible mechanical properties and easy fabrication, and are mostly 'phonon glasses'. However, the thermoelectric performances of these organic materials are largely limited by low molecular order and they are therefore far from being 'electron crystals'. Here, we report a molecularly n-doped fullerene derivative with meticulous design of the side chain that approaches an organic 'PGEC' thermoelectric material. This thermoelectric material exhibits an excellent electrical conductivity of >10 S cm−1 and an ultralow thermal conductivity of <0.1 Wm−1K−1, leading to the best figure of merit ZT = 0.34 (at 120 °C) among all reported single-host n-type organic thermoelectric materials. The key factor to achieving the record performance is to use 'arm-shaped' double-triethylene-glycol-type side chains, which not only offer excellent doping efficiency (~60%) but also induce a disorder-to-order transition upon thermal annealing. This study illustrates the vast potential of organic semiconductors as thermoelectric materials. Achieved high thermoelectric figure of merit (ZT) in organic thermoelectric materials remains a challenge due to their low packing order and poor host/dopant miscibility. Here, the authors report side chain-engineered n-doped fullerene derivatives with record ZT >0.3 for organic thermoelectrics. [ABSTRACT FROM AUTHOR]

Inexpensive and easy-to-use diagnostic tools for fast health screening are imperative, especially in the developing world, where portability and affordability are a necessity. Accurate monitoring of metabolite levels can provide useful information regarding key metabolic activities of the body and detect the concomitant irregularities such as in the case of diabetes, a worldwide chronic disease. Today, the majority of daily glucose monitoring tools rely on piercing the skin to draw blood. The pain and discomfort associated with finger pricking have created a global need to develop non-invasive, portable glucose assays. In this work, we develop a disposable analytical device which can measure physiologically relevant glucose concentrations in human saliva based on enzymatic electrochemical detection. We use inkjet-printing technology for the rapid and low-cost deposition of all the components of this glucose sensor, from the electronics to the biorecognition elements, on commercially available paper substrates. The only electronic component of the sensor is the conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), while the biorecognition element comprises of the enzyme glucose oxidase coupled with an electron mediator. We demonstrate that one month after its fabrication and storage in air-free environment, the sensor maintains its function with only minor performance loss. This fully printed, all-polymer biosensor with its ease of fabrication, accuracy, sensitivity and compatibility with easy-to-obtain biofluids such as saliva aids in the development of next generation low-cost, non-invasive, eco-friendly, and disposable diagnostic tools. Glucose in saliva tested by paper sensors: Saliva based glucose test can now be made easily and cheaply with inkjet-printed paper sensors enabled by enzyme glucose oxidase. Most present technologies rely on blood tests to monitor glucose concentration. To tackle this problem, a collaborative international team led by Prof Sahika Inal from King Abdullah University of Science and Technology, Saudi Arabia designs disposable glucose sensors based on saliva testing. They construct the analytical device by ink-jet printing cheap conducting polymer, an enzyme containing biological film and an encapsulation layer on paper substrates to measure glucose concentrations in human saliva. The devices stay active for more than a month in air-free storage conditions with minor performance losses. The high versatility and adaptability of the material system enable the possibilities to design affordable and expandable enzyme testing based diagnostic platforms. [ABSTRACT FROM AUTHOR]