Intercrystallite molecular connections are widely recognized to tremendously impact the macroscopic properties of semicrystalline polymers. Because it is challenging to directly probe such ...connections, theoretical frameworks have been developed to quantify their concentrations and predict the mechanical properties that result from these connections. Tie-chain connectivity similarly impacts the electrical properties in semicrystalline conjugated polymers. Yet, its quantitative impact has eluded the community. Here, we assess the Huang–Brown model, a framework commonly used to describe the structural origins of mechanical properties in polyolefins, to quantitatively elucidate the effect of tie chains on the electrical properties of a model conjugated polymer. We found that a critical tie-chain fraction of 10–3 is needed to support macroscopic charge transport, below which intercrystallite connectivity limits charge transport, and above which intracrystallite disorder is the bottleneck. Extending the Huang–Brown framework to conjugated polymers enables the prediction of macroscopic electrical properties based on experimentally accessible morphological parameters. Our study implicates the importance of long and rigid polymer chains for efficient charge transport over device length scales.
Achieving intimate mixing in immiscible polymer blend thin films is of paramount importance for maximizing their performance in numerous applications such as membranes, electronics, and energy ...devices. Here, we introduce a promising approach to confine and stabilize phase separation in an immiscible polymer mixture using a bottom-up technique termed matrix-assisted pulsed laser evaporation (MAPLE). Using polyethylene/poly(methyl methacrylate) as a model blend system, we demonstrate that the mechanism of thin-film growth by MAPLE, which geometrically confines a polymer into nanometer- to micrometer-size clusters during film formation, can act to kinetically trap strongly immiscible polymer mixtures, which in turn limits the extent of phase separation of the resulting film without the need for compatibilizers. Due to the unique morphology, the films exhibit distinct thermal properties in comparison to macroscopically phase-separated films. Our results present a promising technique for polymer thin-film fabrication and blending, which could inspire the design of thin films with exceptionally integrated properties.
The mechano‐electrical properties of poly(3‐hexylthiophene) thin films are investigated as a function of their tie‐chain content. Tie chains play an indispensable role in enabling strain‐induced ...structural alignment and charge‐transport enhancement in the strain direction. In the absence of sufficient tie chains, the external mechanical force cannot induce any significant polymer backbone alignment locally or crystallite reorientation at the mesoscale. These samples instead undergo brittle fracture on deformation, with cracks forming normal to the direction of strain; charge transport in this direction is hindered as a consequence. This mechanistic insight on strain alignment points to the promise of leveraging tie‐chain fraction as a practical tuning knob for effecting the mechano‐electrical properties in conjugated polymer systems.
The impact of tie chains on the mechano‐electrical properties of conjugated polymers is investigated. Structural and electrical characterizations show that polymer films need to have sufficient tie‐chain connectivity to exhibit strain‐induced polymer backbone alignment locally, and crystallite reorientation at the mesoscale, which jointly lead to improved macroscopic charge transport along the strain direction.
Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene "universal crystal engineering core". After computationally screening derivatives, a ...trialkylsilylethyne-based crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm
2
V
−1
s
−1
.
Silylethyne-functionalized benzodithiophene serves as a universal crystal engineering core to yield stable, soluble, π-stacked arrays of aromatic chromophores.
•Rigorous treatment of heat exchanger network matching graph as a bipartite graph.•Identification of which part in the Pinch Technology algorithm introduces loops in the resulting ...network.•Identification of requirement of planarity of resulting graph for the valid application of Euler's rule relating number of loops with number of heat exchanger units.•Demonstration by counter examples that planarity is not guaranteed by the heat integration process hence use of Euler's rule on the total network cannot be guaranteed to predict correctly the number of loops.
Pinch Technology developed by Linnhoff and other workers has been widely adopted and considered to be one of the most successful techniques in process energy integration. The number of heat exchanger units is one of the most important aspects in the problem and Euler's formula has been applied in correlating the number of units and loops in the network. However, planarity of a graph is required for the application of Euler's formula, a fact that has been ignored in previous literature. It is demonstrated in this paper that Euler's formula cannot always be applied in Pinch Technology, by presenting examples of non-planar graphs resulting from thermodynamically feasible heat exchanger networks.
While typical perovskite solar cells (PSCs) with doped Spiro-OMeTAD as a hole transport material (HTM) have shown rapid increase in their power-conversion efficiencies (PCEs), their poor stability ...remains a big concern as the dopants and additives used with Spiro-OMeTAD have a strong tendency to diffuse into and degrade the perovskite active layer under normal operating conditions. Aiming to push forward the development of PSCs, many dopant-free small-molecular HTMs have been reported based on energetic considerations for charge transfer and criteria for charge transport. However, the PCEs of the state-of-the-art PSCs with dopant-free small-molecular HTMs are still inferior to those using doped Spiro-OMeTAD, and little attention has been paid to the interactions between the HTM and perovskite absorber in PSCs. Here, we report a facile design concept to functionalize HTMs so that they can passivate perovskite surface defects and enable perovskite active layers with lower density of surface trap states and more efficient charge transfer to the hole transport layer. As a consequence, perovskite solar cells with a functionalized HTM exhibit a champion PCE of 22.4%, the highest value for PSCs using dopant-free small molecular HTMs to date, and substantively improved operational stability under continuous illumination. With a
T
80
of (1617 ± 7) h for encapsulated cells tested at 30 °C in air, the PSCs containing the functionalized HTM are among the most stable PSCs using dopant-free small-molecular HTMs. The effectiveness of our strategy is demonstrated in PSCs comprising both a state-of-the-art MA-free perovskite and MAPbI, a system having more surface defects, and implies the potential generality of our strategy for a broad class of perovskite systems, to further advance highly efficient and stable solar cells.
Incorporation of a hole-transport material that also passivates surface defects results in perovskite solar cells with superior efficiency and stability.
Size exclusion chromatography (SEC) is not well suited for characterizing the molecular weight (MW) and MW distribution of conjugated polymers, especially those that absorb strongly at the detection ...wavelengths, or those that interact with and adsorb on the walls of SEC columns. We demonstrate diffusion-ordered NMR spectroscopy (DOSY) as a complementary method for characterizing the size and size distribution of conjugated polymers. Starting with four batches of poly(3-hexylthiophene), whose distinct and narrow MW distributions had been fully characterized, as a model system, we establish a power-law relationship between the weight-average MW and the diffusion coefficient measured through DOSY. We extend this approach to characterizing poly4-(4,4-dihexadecyl-4H-cyclopenta1,2-b:5,4-b′dithiophen-2-yl)-alt-1,2,5thiadiazolo-3,4-cpyridine, whose absorption properties preclude its characterization with light scattering based techniques, including SEC. By applying the same power law on the diffusion coefficients obtained by DOSY measurements, we extracted P3HT-equivalent MWs and MW distributions for six different batches of PCDTPT. By circumventing the practical issues in SEC measurements, DOSY shows promise as a versatile complement for determining polymer size.
Correction for A hole-transport material that also passivates perovskite surface defects for solar cells with improved efficiency and stability by Xiaoming Zhao
et al.
,
Energy Environ. Sci.
, 2020,
...13
, 43344343,
https://doi.org/10.1039/D0EE01655A
.
Most contemporary X‐ray detectors adopt device structures with non/low‐gain energy conversion, such that a fairly thick X‐ray photoconductor or scintillator is required to generate sufficient ...X‐ray‐induced charges, and thus numerous merits for thin devices, such as mechanical flexibility and high spatial resolution, have to be compromised. This dilemma is overcome by adopting a new high‐gain device concept of a heterojunction X‐ray phototransistor. In contrast to conventional detectors, X‐ray phototransistors allow both electrical gating and photodoping for effective carrier‐density modulation, leading to high photoconductive gain and low noise. As a result, ultrahigh sensitivities of over 105 μC Gyair−1 cm−2 with low detection limit are achieved by just using an ≈50 nm thin photoconductor. The employment of ultrathin photoconductors also endows the detectors with superior flexibility and high imaging resolution. This concept offers great promise in realizing well‐balanced detection performance, mechanical flexibility, integration, and cost for next‐generation X‐ray detectors.
An ultrathin and ultrasensitive direct X‐ray detector based on a heterojunction phototransistor is developed by taking advantage of high‐gain and gating‐modulation mechanisms. This unique device concept allows for a significant reduction in X‐ray photoconductor thickness while maintaining high sensitivity and low detection limit, which opens up new opportunities for developing high‐resolution, flexible, and low‐cost X‐ray direct detectors.
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