Search

Designing high-efficiency bifunctional photocatalysts toward photoinduced overall water splitting is one of the most promising and challenging research directions for clean energy generation. By employing static electronic structure calculation and nonadiabatic molecular dynamics (NAMD) simulation, we herein established a recently synthesized two-dimensional (2D) aza-fused covalent organic framework (aza-COF) as a potential bifunctional photocatalyst toward overall water splitting reactions. Our calculated results reveal that the overpotentials for hydrogen evolution reaction and oxygen evolution reaction are only 0.06 and 0.31 V, respectively, at pH = 4. The dynamics of photoexcited charge carriers studied through NAMD simulation predicts the electron-hole recombination time (25.15 ns), and this confirms that the photogenerated electron and hole carriers migrate to the active sites for the occurrence of reaction before they recombine. Therefore, our results suggest that the 2D aza-COFs exhibit great potential as metal-free and single-material photocatalysts toward overall water splitting under visible light.

The argyrodite family has emerged as a promising thermoelectric candidate due to its highly diffusive Ag ions and inherent low thermal conductivity. To address issues that commonly arise with hot pressing (HP) sintering, this study proposes to use the zone melting (ZM) method to synthesize high-density polycrystalline bulk Ag 8 SnSe 6 samples. The thermoelectric properties of samples synthesized by the ZM and HP methods were thoroughly evaluated over a temperature range of 300 to 700 K. Due to the weaker scattering of electrons, the ZM-synthesized samples exhibited an ∼60% increase in weighted mobility, compared to those produced by the HP method. Despite the slight increase in thermal conductivity, the specimen synthesized by the ZM method achieves a higher peak zT value of 1.05 at 700 K. The average zT value also improves to 0.71 across the temperature range of 300 to 700 K. This work demonstrates the effectiveness of the ZM method in enhancing the thermoelectric performance of Ag 8 SnSe 6 , with great potential applicability to other argyrodite compounds.

GeTe stands as a promising lead-free medium-temperature thermoelectric material that has garnered considerable attention in recent years. Suppressing carrier concentration by aliovalent doping in GeTe-based thermoelectrics is the most common optimization strategy due to the intrinsically high Ge vacancy concentration. However, it inevitably results in a significant deterioration of carrier mobility, which limits further improvement of the zT value. Thus, an effective Trojan doping strategy via CuScTe 2 alloying is utilized to optimize carrier concentration without intensifying charge carrier scattering by increasing the solubility of Sc in the GeTe system. Because of the high doping efficiency of the Trojan doping strategy, optimized hole concentration and high mobility are obtained. Furthermore, CuScTe 2 alloying leads to band convergence in GeTe, increasing the effective mass m * in (Ge 0.84 Sb 0.06 Te 0.9 )(CuScTe 2 ) 0.05 and thus significantly improving the Seebeck coefficient throughout the measured temperature range. Meanwhile, the achievement of the ultralow lattice thermal conductivity ( κ L ∼ 0.34 W m -1 K -1 ) at 623 K is attributed to dense point defects with mass/strain-field fluctuations. Ultimately, the (Ge 0.84 Sb 0.06 Te 0.9 )(CuScTe 2 ) 0.05 sample exhibits a desirable thermoelectric performance of zT max ∼ 1.81 at 623 K and zT ave ∼ 1.01 between 300 and 723 K. This study showcases an effective doping strategy for enhancing the thermoelectric properties of GeTe-based materials by decoupling phonon and carrier scattering.

The exploration of novel two-dimensional (2D) materials with a direct band gap and high mobility has attracted huge attention due to their potential application in electronic and optoelectronic devices. Here, we propose a feasible way to construct multiatomic monolayer Ca 2 A 2 Z 5 (A = Al and Ga and Z = S, Se, and Te) by first-principles calculations. Our results indicated that the energies of α 1 -phase Ca 2 A 2 Z 5 are slightly lower than those of experimentally synthesized α 3 -phase-like Ca 2 A 2 Z 5 monolayers with excellent structural stability. Moreover, the α 1 - and α 3 -phase Ca 2 A 2 Z 5 monolayers possess not only direct band gaps but also high electron mobilities (up to ∼10 3 cm 2 V -1 s -1 ), demonstrating an intriguing range of visible light absorption. Importantly, α 1 - and α 3 -phase Ca 2 Ga 2 Se 5 monolayers are good donor materials, and the corresponding Ca 2 Ga 2 Se 5 /ZrSe 2 type-II heterostructures exhibit desirable power conversion efficiencies of 22.4% and 22.9%, respectively. Our findings provide a feasible way to explore new 2D materials and offer several Ca 2 A 2 Z 5 candidate monolayers for the application of high-performance solar cells.

We theoretically identify the ScSeI monolayer as a promising new 2D material for photocatalysis through first-principles calculations. The most notable feature is the significant difference in carrier mobility, with electron mobility in the horizontal direction being 20.66 times higher than hole mobility, minimizing electron-hole recombination. The ScSeI monolayer exhibits a bandgap of 2.51 eV, with the valence band maximum at -6.37 eV and the conduction band minimum at -3.86 eV, meeting the requirements for water splitting. Phosphorus doping lowers the Gibbs free energy by 1.63 eV, enhancing the catalytic activity. The ScSeI monolayer achieves a hydrogen production efficiency of 17%, surpassing the commercial threshold of 10% and shows excellent mechanical, thermal, and dynamic stability, indicating feasibility for experimental synthesis and practical application. Additionally, the monolayer maintains its photocatalytic properties under tensile strain (-6% to 6%) and in aqueous environments, reinforcing its potential as an effective photocatalyst. Based on these findings, we believe the ScSeI monolayer is a highly promising photocatalyst.

Halide perovskite nanocrystals (NCs), specifically CsPbBr 3 , have attracted considerable interest due to their remarkable optical properties for optoelectronic devices. To achieve high-efficiency light-emitting diodes (LEDs) based on CsPbBr 3 nanocrystals (NCs), it is crucial to optimize both their photoluminescence quantum yield (PLQY) and carrier transport properties when they are deposited to form films on substrates. While the exchange of native ligands with didodecyl dimethylammonium bromide (DDAB) ligand pairs has been successful in boosting their PLQY, dense DDAB coverage on the surface of NCs should impede carrier transport and limit device efficiency. Following our previous work, here, we use oleyl phosphonic acid (OLPA) as a selective stripping agent to remove a fraction of DDAB from the NC surface and demonstrate that such stripping enhances carrier transport while maintaining a high PLQY. Through systematic optimization of OLPA dosage, we significantly improve the performance of CsPbBr 3 LEDs, achieving a maximum external quantum efficiency (EQE) of 15.1% at 516 nm and a maximum brightness of 5931 cd m -2 . These findings underscore the potential of controlled ligand stripping to enhance the performance of CsPbBr 3 NC-based optoelectronic devices.

The thermoelectric performance of n-type Bi 2 Te 3 needs further enhancement to match that of its p-type Bi 2 Te 3 counterpart and should be considered for competitive applications. Combining Cu/Cl and multiscale additives (AgBiSe 2 ) presents a suitable route for such enhancement. This is evidence of the enhanced thermoelectric performance of Bi 1.995 Cu 0.005 Te 2.69 Se 0.33 Cl 0.03 . Moreover, by incorporating 0.65 wt % AgBiSe 2 (ABS) into Bi 1.995 Cu 0.005 Te 2.69 Se 0.33 Cl 0.03 , we further reduce its lattice thermal conductivity to ∼0.28 W m -1 K -1 at 353 K owing to the extra phonon scattering of multiscale ABS. Additionally, the Seebeck coefficient enhances (-183.89 μV K -1 at 353 K) owing to the matrix's reduced carrier concentration caused by ABS. As a result, we achieve a high ZT of ∼1.25 (at 353 K) and a high ZT ave of ∼1.12 at 300-433 K for Bi 1.995 Cu 0.005 Te 2.69 Se 0.33 Cl 0.03 + 0.65 wt % ABS. This work provides a promising strategy for enhancing the thermoelectric performance of n-type Bi 2 Te 3 through Cu/Cl doping and ABS incorporation.

Thermally activated delayed fluorescent (TADF) materials are naturally bipolar and can potentially serve as hosts. However, triplet excitons in TADF materials are long-lived and prone to unfavorable bimolecular processes. Implementing an efficient reverse system intersection (RISC) process is an effective solution. Moreover, although the general TADF host is bipolar, polarity differences still cause a mobility imbalance. In this work, we designed and synthesized a novel TADF host material, 11-(3-(4-(3-bromophenyl)-6-phenyl-1,3,5-triazin-2-yl)phenyl)-12,12-dimethyl-11,12-dihydroindeno[2,1- a ]carbazole (Br-DMIC-TRZ). The upconversion of the TADF host and its doped films is facilitated due to enhanced spin-orbit coupling (SOC) induced by bromine, which exhibits a higher rate of RISC. This progress facilitates the involvement of more triplet excitons in luminescence. Meanwhile, the attachment of bromine to the acceptor fragment of TADF enhances the electron mobility, where hole mobility and electron mobility are more comparable. Enhanced exciton upconversion and balanced carrier transport allow devices formed based on brominated TADF hosts to outperform other hosts. The Br-TADF-based devices with three dopants sensitized achieved improvements of 29.8, 21.4, and 24.4% compared to the DMIC-TRZ-based device. This work provides a feasible molecular design strategy for further developing efficient hosts.

Graphene-hexagonal boron nitride (hBN) scalable heterostructures are pivotal for the development of graphene-based high-tech applications. In this work, we demonstrate the realization of high-quality graphene-hBN heterostructures entirely obtained with scalable approaches. hBN continuous films were grown via ion beam-assisted physical vapor deposition directly on commercially available SiO 2 /Si and used as receiving substrates for graphene single-crystal matrixes grown by chemical vapor deposition on copper. The structural, chemical, and electronic properties of the heterostructure were investigated by atomic force microscopy, Raman spectroscopy, and electrical transport measurements. We demonstrate graphene carrier mobilities exceeding 10,000 cm 2 /Vs in ambient conditions, 30% higher than those directly measured on SiO 2 /Si. We prove the scalability of our approach by measuring more than 100 transfer length method devices over a centimeter scale, which present an average carrier mobility of 7500 ± 850 cm 2 /Vs. The reported high-quality all-scalable heterostructures are of relevance for the development of graphene-based high-performing electronic and optoelectronic applications.

The morphological characteristics of the GaN nonpolar sidewalls with different crystal plane orientations were studied under various TMAH wet treatment conditions, and the effect of different morphological features on device carrier mobility was modeled and analyzed. After TMAH wet treatment, the morphology of the a -plane sidewall presents multiplied zigzag triangular prisms along the [0001] direction, which consist of two adjacent m- plane and c -plane on top. While along the [112̅0] direction, the m -plane sidewall is represented by thin, striped prisms with three m -plane and a c -plane on the side. The density and size of sidewall prisms were studied by varying the solution temperature and immersion period. The prism density decreases linearly as the solution temperature rises. With increased immersion time, both a -plane and m -plane sidewalls show smaller prism sizes. Vertical GaN trench MOSFET with nonpolar a - and m -plane sidewall channels were fabricated and characterized. By properly treated in TMAH solution, transistors with an a -plane sidewall conduction channel exhibit higher current density, from 241 to 423 A cm -2 @ V DS = 10 V, V GS = 20 V, and higher mobility, from 2.9 to 2.0 cm 2 -plane sidewall devices. The temperature dependence on mobility is also discussed, and a modeling analysis for the difference in carrier mobility is then performed.-1 , compared to those of m -plane sidewall devices. The temperature dependence on mobility is also discussed, and a modeling analysis for the difference in carrier mobility is then performed.

Two-dimensional (2D) van der Waals (vdW) layered materials have provided novel opportunities to explore interesting physical properties such as thickness-dependent bandgap, moiré excitons, superconductivity, and superfluidity. However, the presence of interlayer resistance along the thickness and Schottky barrier in metal-to-2D vdW semiconducting materials causes a limited interlayer charge injection efficiency, perturbing various intrinsic properties of 2D vdW multilayers. Herein, we report a simple but powerful contact electrode design to enhance interlayer carrier injection efficiency along the thickness by constructing vertical double-side contact (VDC) electrodes. A 2-fold extended contact area of VDC not only strongly limits an interlayer resistance contribution to the field-effect mobility and current density at the metal-to-2D semiconductor interface but also significantly suppresses both current transfer length (≤1 μm) and specific contact resistivity (≤1 mΩ·cm 2 ), manifesting clear benefits of VDC in comparison with those in conventional top-contact and bottom-contact configurations. Our layout for contact electrode configuration may suggest an advanced electronic device platform for high-performing 2D optoelectronic devices.

An aligned semiconducting carbon nanotube (A-CNT) array has been considered an excellent channel material to construct high-performance field-effect transistors (FETs) and integrated circuits (ICs). The purification and assembly processes to prepare a semiconducting A-CNT array require conjugated polymers, introducing stubborn residual polymers and stress at the interface between A-CNTs and substrate, which inevitably affects the fabrication and performance of the FETs. In this work, we develop a process to refresh the Si/SiO 2 substrate surface underneath the A-CNT film by wet etching to clean the residual polymers and release the stress. Top-gated A-CNT FETs fabricated with this process show significant performance improvement especially in terms of saturation on-current, peak transconductance, hysteresis, and subthreshold swing. These improvements are attributed to the increase in carrier mobility from 1025 to 1374 cm 2 /Vs by 34% after the substrate surface refreshing process. Representative 200 nm gate-length A-CNT FETs exhibit an on-current of 1.42 mA/μm and a peak transconductance of 1.06 mS/μm at a drain-to-source bias of 1 V, subthreshold swing (SS) of 105 mV/dec, and negligible hysteresis and drain-induced barrier lowering (DIBL) of 5 mV/V.

Simultaneously realizing improved carrier mobility and good photoluminescence (PL) efficiency in red thermally activated delayed-fluorescence (TADF) emitters remains challenging but important. Herein, two isomeric orange-red TADF emitters, o PDM and p PDM, with the same basic donor-acceptor backbone but a pyrimidine ( Pm ) attachment at different positions are designed and synthesized. The two emitters show similarly good PL properties, including narrow singlet-triplet energy offsets (0.11 and 0.15 eV) and high photoluminescence quantum yields (ca. 100 and 88%) in doped films. An orange-red organic light-emitting diode (OLED) employing o PDM as an emitter achieves an almost twice as high maximum external quantum efficiency (28.2%) compared with that of a p PDM-based OLED. More balanced carrier-transporting properties are responsible for their contrasting device performances, and the position effect of the Pm substituent leads to significantly distinct molecular packing behaviors in the aggregate states and different carrier mobilities.

To date, measuring the carrier mobility in semiconductor films, especially for the amorphous organic small-molecule films, is still a big challenge. Here, we demonstrate that transient electroluminescence (TrEL) spectroscopy with quantum-dot light-emitting diodes as the platform is a feasible and reliable method to evaluate the carrier mobility of such amorphous films. The position of the exciton formation zone is precisely determined and controlled by employing a quantum dot monolayer as the emissive layer. The electrical field intensity across the organic layer is evaluated through the charge density at the electrode calculated by the transient current. Then, the charge carrier mobility is obtained by combining the electroluminescence (EL) delay time and the thickness of the organic layer. Additionally, we demonstrate that the large roughness of the organic layer leads to serious charge accumulation and, hence, a high localized electrical field, which provides preferred charge injection paths, reducing the EL delay time and underestimating the EL delay time. Therefore, a thick organic film is the prerequisite for a reliable measurement of charge carrier mobility, which can circumvent the negative effect of film roughness.

GeTe is an emerging lead-free thermoelectric material, but its excessive carrier concentration and high thermal conductivity severely restrict the enhancement of thermoelectric properties. In this study, the synergistically optimized thermoelectric properties of p-type GeTe through Bi-Cu 2 S coalloying are reported. It can be found that the donor behavior of Bi and the substitution-interstitial defect pairs of Cu + ions effectively reduce the hole concentration to an optimal level with carrier mobility less affected. At the same time, Bi-Cu 2 S coalloying induces many phonon scattering centers involving stacking faults, nanoprecipitations, grain boundaries and tetrahedral dislocations and suppresses the lattice thermal conductivity to 0.64 W m -1 K -1 . Consequently, all effects synergistically yield a peak ZT of 1.9 at 770 K with a theoretical conversion efficiency of 14.5% (300-770 K) in the (Ge 0.94 Bi 0.06 Te) 0.988 (Cu 2 S) 0.012 sample, which is very promising for mid-low temperature range waste heat harvest.

Lead-free SnTe-based materials are expected to replace PbTe and have gained much attention from the thermoelectric community. In this work, a maximum ZT of ∼1.31 at 873 K is attained in SnTe via promoting a high quality factor resulting from Mn alloying and BiBr 3 doping. The results show that Mn alloying in SnTe converges the L band and the ∑ band in valence bands to supply enhanced valley degeneracy and the density of states effective mass, giving rise to a high power factor of ∼21.67 μW cm -1 K -2 at 723 K in Sn 0.93 Mn 0.1 Te. In addition, the subsequent BiBr 3 doping can sharpen the top of the valence band to coordinate the contradiction between the band effective mass and the carrier mobility, thus enhancing the carrier mobility while maintaining a relatively large density of states effective mass. Consequently, a maximum power factor of 23.85 μW cm -1 K -2 at 873 K is achieved in Sn 0.93 Mn 0.1 Te-0.8 atom % BiBr 3 . In addition to band sharpening, BiBr 3 doping can also effectively suppress the bipolar effect at elevated temperatures and reduce the lattice thermal conductivity by strengthening the point defect phonon scattering. Benefitting from doping BiBr 3 in Sn 0.93 Mn 0.1 Te optimizes the carrier mobility and suppresses the lattice thermal conductivity, resulting in a dramatically enhanced quality factor. Accordingly, an average ZT of ∼0.62 in the temperature range of 300-873 K is obtained in Sn 0.93 Mn 0.1 Te-0.8 atom % BiBr 3 , ∼250% increase compared with that in Sn 1.03 Te.

The GeTe compound has been revealed to be an outstanding thermoelectric compound, while its inherent high thermal conductivity restricts further improvement in its performance. Herein, we report a study on the synergistic optimization of the thermoelectric performance of GeTe by Bi-Se codoping. It is shown that the introduction of Bi decreases the carrier concentration and increases the structural parameter of the interaxial angle. With Se doping in the Te site, the lattice thermal conductivity is markedly reduced, while the carrier mobility is slightly influenced. Compared with the singly Se-doped GeTe, the Ge 1- x Bi x Te 1 -y Se y samples are more closed to a cubic phase, as indicated by the larger interaxial angle. On account of the reduction of carrier concentration and thermal conductivity, a ZT max of 1.80 at 665 K and a high ZT ave of 1.39 (400-800 K) are obtained in Ge 0.94 Bi 0.06 Te 0.85 Se 0.15 . This work reveals that the interaxial angle is vital to the performance optimization of rhombohedral GeTe.

Mg 3 Sb 2 -based compounds are promising thermoelectric materials because of their excellent thermoelectric performance, low cost, and good mechanical properties. In this work, Er, Dy, Gd, and Nd are all confirmed to be effective n-type dopants for optimizing the carrier concentration, increasing the density of states effective mass, and suppressing the ionized impurity scattering of Mg 3 Sb 2 -based compounds. By increasing the sintering temperature, a larger grain size can be achieved and can effectively improve the carrier mobility in the whole measured temperature range. As a result, maximum zT values above ∼1.6 at 673 K and average zT s above ∼1.0 between 300 and 673 K were achieved for Mg 3.07 Er 0.03 Bi 0.5 Sb 1.5 , Mg 3.07 Dy 0.03 Bi 0.5 Sb 1.5 , and Mg 3.07 Nd 0.03 Bi 0.5 Sb 1.5 . In addition, a high compressive strength of ∼180 MPa was obtained in Mg 3.07 Dy 0.03 Bi 0.5 Sb 1.5 . Therefore, rare-earth element-doped Mg 3 Sb 2 -based compounds are promising for thermoelectric applications.

Small-bandwidth n-type PbTe-MnTe alloys effectively modify the valley shape, while it also inevitably aggravates the deterioration of carrier mobility as nonpolar phonons dominate the scattering. It is found that a trace amount of Cu doping can alleviate the compromises among thermoelectric parameters, thereby significantly optimizing the electrical-transport performance near room temperature of n-type PbTe-MnTe alloys. The single-Kane model reveals that the physical origin of performance improvement lies in the carrier mobility enhancement and self-optimization of carrier concentration. The Debye-Callaway model further quantifies the contribution of copper defect scattering to the lattice thermal conductivity. Notably, the high thermoelectric quality factor obtained in this work rationalizes their superior properties and reveals immense potential for achieving higher zT. Herein, an extremely high zT of ∼0.52 at room temperature and a maximum zT max of ∼1.2 at 823 K are achieved in 0.3% Cu-intercalated n-type PbTe-MnTe. The mechanism in balancing compromise elaborated in principle contributes to an improvement of thermoelectric properties of the n-type PbTe alloys in a broad temperature range.

2D semiconductors with atomically thin body thickness have attracted tremendous research interest for high-performance nanoelectronics and optoelectronics. Most of the 2D semiconductors grown by chemical vapor deposition (CVD) methods suffer from rather low carrier mobility, small single-crystal size, and instability under ambient conditions. Here, we develop an improved CVD method with controllable reverse-gas flow to realize the direct growth of quality Bi 2 O 2 Se 2D single crystals on a mica substrate. The applied reverse flow significantly suppresses the random nucleation and thus promotes the lateral size of 2D Bi 2 O 2 Se crystals up to ∼750 μm. The Bi 2 O 2 Se field-effect transistors display high-room-temperature electron mobility up to ∼1400 cm 2 ·V -1 ·s -1 and a well-defined drain current saturation. The on/off ratio of the Bi 2 O 2 Se transistor is larger than 10 7 , and the sub-threshold swing is about 90 mV·dec -1 . The responsivity, response time, and detectivity of Bi 2 O 2 Se photodetectors approach up to 60 A·W -1 , 5 ms, and 2.4 × 10 10 Jones at room temperature, respectively. Our results demonstrate large-size and high-quality Bi 2 O 2 Se grown by reverse-flow CVD as a high-performance channel material for next-generation transistors and photodetectors.

Perovskite-perovskite tandem solar cells have bright prospects to improve the power conversion efficiency (PCE) beyond the Shockley-Queisser (SQ) limit of single-junction solar cells. The star lead-based halide perovskites are well-recognized as suitable candidates for the front cell, thanks to their suitable band gap (∼1.8 eV), strong optical absorption, and high certified PCE. However, the toxicity of lead for the front cell and the lack of a narrow band gap (∼1.1 eV) for the rear cell seriously restrict the development of the two-junction tandem cell. To break through this bottleneck, a novel Dion-Jacobson (DJ)-type ( n = 2) chalcogenide perovskite CsLaM 2 X 7 (M = Ta, Nb; X = S, Se) has been found based on the powerful first-principles and advanced many-body perturbation GW calculations. Their excellent electronic, transport, and optical properties can be summarized as follows. (1) They are stable and environmentally friendly lead-free materials. (2) The direct band gap of CsLaTa 2 Se 7 (0.96-1.10 eV) is much smaller than those of lead-based halide perovskites and very suitable for the rear cell in the two-junction tandem cell. (3) The carrier mobility in CsLaTa 2 Se 7 reaches 1.6 × 10 3 cm 2 V -1 s -1 at room temperature. (4) The absorption coefficients (3-5 × 10 5 cm -1 ) are 1 order higher than that of Si (10 4 cm -1 ). (5) The estimated PCEs of the Cs 2 Sb 2 Br 8 -CsLaTa 2 Se 7 tandem cell (33.3%) and the concentrator solar cell (35.8% in 100 suns) are higher than those of the best recorded GaAs-Si tandem cell (32.8%) and the perovskite-perovskite tandem solar cell (24.8%). These energetic results strongly demonstrate that the novel lead-free chalcogenide perovskites CsLaM 2 X 7 are good candidates for the rear cell of tandem cells.

We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C 3 N 5 is a low-band-gap ( E g = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C 3 N 5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C 3 N 5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm 2 V -1 s -1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm 2 V -1 s -1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J-V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C 3 N 5 in CdS-MHP. C 3 N 5 , with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core-shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.

Chemical transformation of typically "nonlayered" phases into two-dimensional structures remains a formidable task. Among the thickness tunable CsPbX 3 ( X = Br, Br/I, I) nanosheets (NSs), CsPbBr 1.5 I 1.5 NSs with a thickness of ∼4.9 nm have structural stability superior to ∼6.8 nm CsPbI 3 NSs and better hole mobility than ∼3.7 nm CsPbBr 3 NSs. Moving beyond the much-explored CsPbBr 3 photodetectors, we demonstrate a sharp improvement of the photodetection of CsPbBr 1.5 I 1.5 NS devices by thickening the NSs to ∼6.1 nm through combining 8-carbon and 18-carbon ligand surfactants. Thereby, the responsivity increases up to one of the highest values of 3313 A W -1 at 1.5 V (and 3946 A W -1 at 2 V) with detectivity of 1.6 × 10 11 Jones at 1.5 V, due to the increase in carrier mobility up to 7.9 × 10 -4 cm 2 V -1 s -1 . The better device performance of the NSs than 8.6-13.9 nm nanocubes (NCs) is due to their planarity which facilitates in-plane mobilization of the charge carriers.

Two-dimensional (2D) semiconductors have been proposed for heterogeneous integration with existing silicon technology; however, their chemical vapor deposition (CVD) growth temperatures are often too high. Here, we demonstrate direct CVD solid-source precursor synthesis of continuous monolayer (1L) MoS 2 films at 560 °C in 50 min, within the 450-to-600 °C, 2 h thermal budget window required for back-end-of-the-line compatibility with modern silicon technology. Transistor measurements reveal on-state current up to ∼140 μA/μm at 1 V drain-to-source voltage for 100 nm channel lengths, the highest reported to date for 1L MoS 2 grown below 600 °C using solid-source precursors. The effective mobility from transfer length method test structures is 29 ± 5 cm 2 V -1 s -1 at 6.1 × 10 12 cm -2 electron density, which is comparable to mobilities reported from films grown at higher temperatures. The results of this work provide a path toward the realization of high-quality, thermal-budget-compatible 2D semiconductors for heterogeneous integration with silicon manufacturing.

Understanding the crystallization mechanism of amorphous metal-oxide thin films remains of importance to avoid the deterioration of multifunctional flexible electronics. We derived the crystallization mechanism of indium-based functional amorphous oxide films by using in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Crystallization begins with surface nucleation, especially at low annealing temperatures, and proceeds simultaneous nucleation and growth in the bulk. Three-dimensional crystal growth in the film was observed when the crystallite size was sufficiently smaller than the film thickness. When the growing crystallites reached the film surface, the crystallization was dominated by two- or lower-dimensional growth. Such crystallization can be explained within the framework of the modified Avrami theory and can be varied for tailoring the electrical properties of the amorphous In 2 O 3 film. After tailoring the film crystallinity and crystallite size, the carrier mobility was improved to >100 cm 2 /V·s in 30 min. Our results show that a carrier mobility of >90 cm 2 /V·s can be implemented for the In 2 O 3 film with a crystallinity of >40% and a crystallite size of >70 nm by an optimized annealing process. The incorporation of Ga element into amorphous In 2 O 3 films obviously increases the activation energy of nucleation and migration. In contrast, Sn dopants can promote the crystal growth. This is attributed to two kinds of migration mechanisms during the annealing in air, one of which is the dominant migration mechanism of oxygen interstitials in crystallized indium-tin oxide (ITO) films and the other dominated by oxygen vacancies in In 2 O 3 and IGO films. Combining the modified Avrami theory with TEM observations, we predicted the structural evolution kinetics for indium-based amorphous oxide films and gained new insights for understanding the temporal structure-functionality relationship during crystallization.

When thickness-dependent carrier mobility is coupled with Thomas-Fermi screening and interlayer resistance effects in two-dimensional (2D) multilayer materials, a conducting channel migrates from the bottom surface to the top surface under electrostatic bias conditions. However, various factors including (i) insufficient carrier density, (ii) atomically thin material thickness, and (iii) numerous oxide traps/defects considerably limit our deep understanding of the carrier transport mechanism in 2D multilayer materials. Herein, we report the restricted conducting channel migration in 2D multilayer ReS 2 after a constant voltage stress of gate dielectrics is applied. At a given gate bias condition, a gradual increase in the drain bias enables a sensitive change in the interlayer resistance of ReS 2 , leading to a modification of the shape of the transconductance curves, and consequently, demonstrates the conducting channel migration along the thickness of ReS 2 before the stress. Meanwhile, this distinct conduction feature disappears after stress, indicating the formation of additional oxide trap sites inside the gate dielectrics that degrade the carrier mobility and eventually restrict the channel migration. Our theoretical and experimental study based on the resistor network model and Thomas-Fermi charge screening theory provides further insights into the origins of channel migration and restriction in 2D multilayer devices.

The nanowire (NW) and gate-all-around (GAA) technologies are regarded as the ultimate solutions to sustain Moore's law benefitting from the exceptional gate control ability. Herein, we conduct a comprehensive ab initio quantum transportation calculation at different diameters (single trigonal-tellurium NW (1Te) and three trigonal-tellrium NW (3Te)) sub-5 nm tellurium (Te) GAA NW metal-oxide-semiconductor field-effect transistors (MOSFETs). The results claim that the performance of 1Te FETs is superior to that of 3Te FETs. Encouragingly, the single Te (1Te) n-type MOSFET with 5 nm gate length achieves International Technology Roadmap for Semiconductors (ITRS) high-performance (HP) and low-dissipation (LP) goals simultaneously. Especially, the HP on-state current reaches 6479 μA/μm, 7 times higher than the goal (900 μA/μm). Moreover, the subthreshold swing of the n-type 1Te FETs even hits a thermionic limit of 60 mV/dec. In terms of the spin-orbit coupling effect, the drain currents of devices are further improved, particularly the p-type Te FETs can also achieve the ITRS HP goal. Hence, the GAA Te MOSFETs provide a feasible approach for state-of-the-art sub-5 nm device applications.

We report a novel approach for engineering tensely strained Si layers on a relaxed silicon germanium on insulator (SGOI) film using a combination of condensation, annealing, and epitaxy in conditions specifically chosen from elastic simulations. The study shows the remarkable role of the SiO 2 buried oxide layer (BOX) on the elastic behavior of the system. We show that tensely strained Si can be engineered by using alternatively rigidity (at low temperature) and viscoelasticity (at high temperature) of the SiO 2 substrate. In these conditions, we get a Si strained layer perfectly flat and free of defects on top of relaxed Si 1- x Ge x . We found very specific annealing conditions to relax SGOI while keeping a homogeneous Ge concentration and an excellent thickness uniformity resulting from the viscoelasticity of SiO 2 at this temperature, which would allow layer-by-layer matter redistribution. Remarkably, the Si layer epitaxially grown on relaxed SGOI remains fully strained with -0.85% tensile strain. The absence of strain sharing (between Si 1- x Ge x and Si) is explained by the rigidity of the Si 1- x Ge x /BOX interface at low temperature. Elastic simulations of the real system show that, because of the very specific elastic characteristics of SiO 2 , there are unique experimental conditions that both relax Si 1- x Ge x and keep Si strained. Various epitaxial processes could be revisited in light of these new results. The generic and simple process implemented here meets all the requirements of the microelectronics industry and should be rapidly integrated in the fabrication lines of large multifinger 2.5 V n-type MOSFET on SOI used for RF-switch applications and for many other applications.

The fundamental challenge for enhancing the thermoelectric performance of n-type PbTe to match p-type counterparts is to eliminate the Pb vacancy and reduce the lattice thermal conductivity. The Cu atom has shown the ability to fill the cationic vacancy, triggering improved mobility. However, the relatively higher solubility of Cu 2 Te limits the interface density in the n-type PbTe matrix, leading to a higher lattice thermal conductivity. In particular, a quantitative relationship between the precipitate scattering and the reduction of lattice thermal conductivity in the n-type PbTe with low solubility of Cu 2 Te alloys still remains unclear. In this work, trivalent Sb atoms are introduced, aiming at decreasing the solubility of Cu in PbTe for improving the precipitate volumetric density and ensuring n-type degenerate conduction. Benefiting from the multiscale hierarchical microstructures by Sb and Cu codoping, the lattice thermal conductivity is considerably decreased to 0.38 W m -1 K -1 . The Debye-Callaway model quantifies the contribution from point defects and nano/microscale precipitates. Moreover, the mobility increases from 228 to 948 cm 2 V -1 s -1 because of the elimination of cationic vacancies. Consequently, a high quality factor is obtained, enabling a superior peak figure of merit ZT of ∼1.32 in n-type Pb 0.975 Sb 0.025 Te by alloying with only ∼1.2% Cu 2 Te. The present finding demonstrates the significant role of low-solubility Cu 2 Te in advancing thermoelectrics in n-type PbTe.

Effective control of the molecular orientation and the degree of ordering in organic semiconductors is important to achieve high-performance organic electronics. Herein, we have successfully achieved highly oriented films in centimeter scale for a naphthalenedicarboximide-based semiconducting polymer (P(NDI2OD-T2)) by solvent vapor annealing (SVA) of precast films under a high magnetic field (HMF). As revealed by the microstructural studies, the SVA-HMF films exhibit a remarkably higher degree of chain alignment and high morphological uniformity compared to the HMF-guided drop-cast films. Based on the structural evolution of the films with the SVA time, a mechanism is proposed to elucidate the alignment process, which emphasizes that the chain aggregates re-formed in the swollen films trigger magnetic alignment and determine the film order. Compared with the unaligned films, field-effect transistors of the magnetic aligned P(NDI2OD-T2) films have exhibited a 19-fold enhancement of electron mobility and an extraordinarily large mobility anisotropy of 125. Furthermore, a significantly reduced energetic barrier for activated transport is observed on the aligned devices from temperature-variable measurements. The improved performance achieved by the HMF-SVA process has indicated its potential for high-performance organic electronic applications.

Carrier mobility is a critical factor for power conversion efficiency (PCE) of polymer solar cells (PSCs), and the low charge carrier mobility still limits the performance improvement of PSCs. Adding high-mobility material into the active layer is one of the better ways to enhance the PCE of PSCs. Two-dimensional (2D) Bi 2 O 2 Se can be an ideal additive material for improving the carrier mobility of PSCs because of its ultrahigh mobility and high thermal stability. In this work, the Bi 2 O 2 Se few-layer 2D nanoflakes are fabricated by combining lithium intercalation with shear force-assisted liquid phase exfoliation and applied as an additive to promote charge transport in PSCs for the first time. The 2D Bi 2 O 2 Se nanoflakes, when introduced into the active layer, not only provide a new interface between a donor and an acceptor and efficient charge transfer pathways but also induce crystallization of the photosensitive layer and form continuous interpenetrating networks, which promotes the exciton separation and charge transfer in the photosensitive layer. As a result, the PCE of a device based on PBDB-T/ITIC is increased from 10.09% (0 wt %) to 12.22% (2 wt %). Meanwhile, the PCE of a device based on PM6/Y6 is also increased from 14.59% for a binary device to 16.28% for an optimized ternary device (2 wt %). Moreover, the optimized ternary device shows excellent air stability by suppressing the mixing of the two phases. This work provides a good method to enhance the PCE of PSCs and also shows that the Bi 2 O 2 Se material has a good prospect in photovoltaic devices.

Interfaces of heterostructures are routinely studied for different applications. Interestingly, monolayers of the same material when interfaced in an unconventional manner can bring about novel properties. For instance, CdS monolayers, stacked in a particular order, are found to show unprecedented potential in the conversion of nanomechanical energy, solar energy, and waste heat into electricity, which has been systematically investigated in this work, using DFT-based approaches. Moreover, stable ultrathin structures showing strong capabilities for all kinds of energy conversion are scarce. The emergence of a very high out-of-plane piezoelectricity, | d 33 | ≈ 56 pm/V, induced by the inversion symmetry broken in the buckled structure helps to supersede the previously reported bulk wurzite GaN, AlN, and Janus multilayer structures of Mo- and W-based dichalcogenides. The piezoelectric coefficients have been found to be largely dependent on the relative stacking between the two layers. CdS bilayer is a direct band gap semiconductor, with its band edges straddling the water redox potential, thereby making it thermodynamically favorable for photocatalytic applications. Strain engineering facilitates its transition from type I to type II semiconductor in CdS bilayer stacked over monolayer boron phosphide, and the theoretically calculated power conversion efficiency (PCE) in the 2D excitonic solar cell exceeds 27% for a fill factor of 0.8, which is much higher than that in ZnO/CdS/CuInGaSe solar cell (20% efficiency). Thermoelectric properties have been investigated using semi classical Boltzmann transport equations for electrons and phonons within the constant relaxation time approximation coupled to deformation potential theory, which reveal ultralow thermal conductivity ( κ l ≈ 0.78 W m -1 K -1 ) at room temperature because of the presence of heavy element Cd, strong anharmonicity (high mode Gruneisen parameter at long wavelength, phonon lifetime <5 ps), low phonon group velocity (4 km/s), and low Debye temperature (260 K). Such a low thermal conductivity is lower than that of dumbbell silicene (2.86 W m -1 K -1 ), SnS 2 (6.41 W m -1 K -1 ) and SnSe 2 (3.82 W m -1 K -1 ), and SnP 3 (4.97 W m -1 ) ≈ 0.8 for p-type and ∼0.7 for n-type doping at room temperature. Its ultrahigh carrier mobility (μ -1 ). CdS bilayer shows a thermoelectric figure of merit ( ZT ) ≈ 0.8 for p-type and ∼0.7 for n-type doping at room temperature. Its ultrahigh carrier mobility (μ e ≈ 2270 cm 2 V -1 s -1 ) is higher than that of single-layer MoS 2 and comparable to that in InSe. The versatile properties of CdS bilayer together with its all-round stability supported by ab initio molecular dynamics simulation, phonon dispersion, and satisfaction of Born-Huang stability criteria highlight its outstanding potential for applications in device fabrication and applications in next-generation nanoelectronics and energy harvesting.

The Zintl compound Mg 3 Sb 2 is a promising thermoelectric material with Earth-abundant components. Compared to its n-type counterpart, p-type Mg 3 Sb 2 reveals lower dimensionless figure of merit ( zT ), principally due to the inferior electronic properties. Herein, p-type Mg 3 Sb 2 materials codoped with Li and Cd have been synthesized via a ball milling plus hot pressing method, and their thermoelectric properties are systematically investigated within the temperature range 300-773 K. Li is found to be an effective hole dopant, which leads to a zT of 0.46 at 773 K in Mg 2.99 Li 0.01 Sb 2 that doubles the zT of Mg 3 Sb 2 . Additional Cd doping further increases carrier mobility ascribed to the weakened polar covalent bonding and diminishes the lattice thermal conductivity simultaneously due to the introduced atomic mass contrast between Cd and Mg. Eventually, the optimized power factor combined with the reduced thermal conductivity has significantly improved the thermoelectric performance of p-type Mg 3 Sb 2 , with Mg 2.69 Li 0.01 Cd 0.5 Sb 2 achieving a maximum zT of ∼0.68 at 773 K and an average zT ave of ∼0.32 over 300-773 K that compare very favorably to those of pristine Mg 3 Sb 2 . This study demonstrates that (Li, Cd) codoping is an effective strategy to enhance the thermoelectric properties of p-type Mg 3 Sb 2 materials.

The thermoelectric hetero nano region, as a new strategy, can effectively modulate the electrical and thermal transport properties. In this study, the thermoelectric hetero nano region is explored to improve the thermoelectric performance for Bi 0.46 Sb 1.54 Te 3 material at room temperature, and a high ZT of 1.45 at 325 K has been achieved. We introduce the thermoelectric hetero nano SnTe regions in a Bi 0.46 Sb 1.54 Te 3 matrix by mechanical alloying and spark plasma sintering technique, which decouples the relation between electrical and thermal transport properties. The improved electrical conductivity can be attributed to the increase in carrier concentration due to the increased point defects and Bi/Sb Te antisite defects. Thermoelectric hetero nano regions effectively scatter the acoustic phonon and thus induce the low lattice thermal conductivity of 0.33 W m -1 K -1 . Due to the synergistic modulation of electrical and thermal transport by the introduction of the thermoelectric hetero nano region, a high ZT value of 1.45 is realized at 325 K.

Potassium-ion batteries (KIBs) have attracted great attention due to their unique advantages including abundant resources, low redox potential of K, and feasible usage of cheap aluminum current collector in battery assembly. In the present work, through first-principles calculations, we find that the recently synthesized two-dimensional T-NiSe 2 is a promising anode material of KIBs. It possesses a large capacity (247 mAh/g), small diffusion barrier (0.05 eV), and low average voltage (0.49 V), rendering T-NiSe 2 a high-performance KIB anode candidate. In addition, we analyze the carrier mobility of T-NiSe 2 , and the results demonstrate that it possesses a superior carrier mobility of 1685 cm 2 /(V s), showing the potential for applications in nanoelectronic devices.

The thermoelectric (TE) community has mainly focused on improving the figure of merit (ZT) of materials. However, the output power of TE devices directly depends on the power factor (PF) rather than ZT. Effective strategies of enhancing PF have been elusive for Bi 2 Te 3 -based compounds, which are efficient thermoelectrics operating near ambient temperature. Here, we report ultrahigh carrier mobility of ∼467 cm 2 V -1 s -1 and power factor of ∼45 μW cm -1 K -2 in a new n-type Bi 2 Te 3 system with nominal composition Cu x Bi 2 Te 3.17 ( x = 0.02, 0.04, and 0.06). It is obtained by reacting Bi 2 Te 3 with surplus Cu and Te and subsequently pressing powder products by spark plasma sintering (SPS). The SPS discharges excess Te but stabilizes the high extent of Cu in the structure, giving unique SPS Cu x Bi 2 Te 3.17 samples. The analyzed composition is close to "Cu x Bi 2 Te 3 ". Their charge transport properties are highly unusual. Hall carrier concentration and mobility simultaneously increase with the higher mole fraction of Cu contrary to the typical carrier scattering mechanism. As a consequence, the electrical conductivity is considerably enhanced with Cu incorporation. The Seebeck coefficient is nearly unchanged by the increasing Cu content in contrast to the general understanding of inverse relationship between electrical conductivity and Seebeck coefficient. These effects synergistically lead to a record high power factor among all polycrystalline n-type Bi 2 Te 3 -based materials.

Size-selected graphene oxide (GO) nanosheets were used to modify the bulk heterojunction (BHJ) morphology and electrical properties of organic photovoltaic (OPV) devices. The GO nanosheets were prepared with sizes ranging from several hundreds of nanometers to micrometers by using a physical sonication process and were then incorporated into PTB7:PC 71 BM photoactive layers. Different GO sizes provide varied portions of the basal plane where aromatic sp 2 -hybridized regions are dominant and edges where oxygenated functional groups are located; thus, GO size distributions affect the GO dispersion stability and morphological aggregation of the BHJ layer. Electron delocalization by sp 2 -hybridization and the electron-withdrawing characteristics of functional groups p-dope the photoactive layer, giving rise to increasing carrier mobilities. Hole and electron mobilities are maximized at GO sizes of several hundreds of nanometers. Consequently, non-geminate recombination is significantly reduced by these facilitated hole and electron transports. The addition of GO nanosheets decreases the recombination order of non-geminate recombination and increases the generated carrier density. This reduction in the non-geminate recombination contributes to an increased power conversion efficiency of PTB7:PC 71 BM OPV devices as high as 9.21%, particularly, by increasing the fill factor to 70.5% in normal devices and 69.4% in inverted devices.

The Seebeck coefficient and carrier mobility in reported doped BiCuSeO system are too small, which limits the improvement of thermoelectric performance. Here, we proposed a novel strategy for optimizing thermoelectric performance by increasing Seebeck coefficient and boosting carrier mobility. We demonstrate that light element Li doping boosts carrier mobility (7.39 cm 2 V -1 s -1 ) due to largely reduced carrier scattering, which results in about 2-fold increase in carrier mobility as compared with reported Bi 0.875 Ba 0.125 CuSeO through modulation doping or microstructure texturing. Moreover, the Seebeck coefficient remarkably increases by contribution of spin entropy induced by magnetic ions Mn incorporation. The enhancement of Seebeck coefficient coupled with enhanced electrical conductivity result in high power factor. Furthermore, nanoprecipitates and dual-atom point defect leads to a significant reduction of lattice thermal conductivity. Therefore, a high ZT value of 0.9 was achieved at 873 K through optimizing power factor while maintaining low thermal conductivity. Our findings provide a new perspective for designing prospective thermoelectric materials.

Screening unique two-dimensional (2D) materials with high mobility and applicable band gaps is motivated by not only the interest in basic science but also the practical applications for photoelectric materials. In this work, we have systematically studied a new family of 2D ternary quintuple layers (QLs), named ABC (A = Na, K, and Rb; B = Cu, Ag, and Au; C = S, Se, and Te). Our results indicate that the QLs of KCuTe, KAgS, KAgSe, KAuTe, RbCuTe, RbAgSe, and RbAgTe host direct band gaps. Moreover, KCuTe, RbCuTe, and RbAgTe QLs show extremely high mobilities of ∼10 4 cm 2 V -1 s -1 . Interestingly, the linear scaling between exciton binding energy and quasiparticle band gap for ABC QLs exhibits an unexpected deviation with the 1/4 law. In addition, KAgSe, KAgS, RbAgSe, and RbAgTe show outstanding power energy conversion efficiencies of up to 21.5%, suggesting that they are good potential donor materials. Our results provide many potential candidates for applications in photoelectric materials, which may be realized in experiments due to the possible exfoliation from their parent compounds.

Photocatalytic water splitting by a two-dimensional material is a promising technology for producing clean and renewable energy. Development of this field requires candidate materials with desirable optoelectronic properties. Here, we present a detailed theoretical investigation of the atomic and electronic structure of few-layer P 4 O 2 systems to predict their optoelectronic properties. We predict that the three-layer P 4 O 2 with normal packing (α-3), ingeniously combining all desired optoelectronic features, is an ideal candidate for photocatalytic water splitting. It fascinatingly bears nearly a direct band gap (1.40 eV), appropriate band edge position, high solar-to-hydrogen efficiency (17.15%), high sunlight absorption efficiency, and ultrahigh carrier mobility (21 460 cm 2 V -1 s -1 ) at room temperature. These results make three-layer P 4 O 2 a promising candidate for photocatalytic water splitting.

We report synthesis of a new poly(4-(4,4-bis(2-ethylhexyl)-4 H-silolo[3,2- b:4,5- b']dithiophene-2-yl)-7-(4,4-bis(2-ethylhexyl)-6-(selenophene-2-yl)-4 H-silolo[3,2- b:4,5- b']dithiophene-2-yl)-5,6-difluorobenzo[ c][1,2,5]thiadiazole (PDFDSe) polymer based on planar 4,7-bis(4,4-bis(2-ethylhexyl)-4 H-silolo[3,2- b:4,5- b']dithiophen-2-yl)-5,6-difluorobenzo[ c][1,2,5]thiadiazole (DFD) moieties and selenophene linkages. The planar backboned PDFDSe polymer exhibits highest occupied molecular orbital and lowest unoccupied molecular orbital levels of -5.13 and -3.56 eV, respectively, and generates well-packed highly crystalline states in films with exclusive edge-on orientations. PDFDSe thin film was incorporated as a channel material in top-gate bottom-contact organic thin-film transistor with a solid-state electrolyte gate insulator (SEGI) composed of poly(vinylidene difluoride-trifluoroethylene)/poly(vinylidene fluoride- co-hexafluroropropylene)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, which exhibited a remarkably high hole mobility up to μ = 20.3 cm 2 V -1 s -1 corresponding to effective hole mobility exceeding 5 cm 2 V -1 s -1 and a very low threshold voltage of -1 V. These device characteristics are associated with the high carrier density in the semiconducting channel region, induced by the high capacitance of the SEGI layer. The excellent carrier mobility from the PDFDSe/SEGI device demonstrates a great potential of semiconducting polymer thin-film transistors as electronic components in future electronic applications.

Large-area, high-quality bilayer graphene (BLG) has attracted great interest because of its immense potential for many viable applications. However, its growth is still greatly limited owing to its small size and low carrier mobility. In this article, we report the successful growth of large-area, high-quality AB-stacked BLG on hexagonal boron nitride (h-BN)/Pt foil by chemical vapor deposition (CVD). Optical microscopy and scanning electron microscopy observations reveal the formation of uniform and continuous BLG films with sizes of up to 500 μm, which are 4-5 times larger than those reported elsewhere for CVD-grown BLG films. A large carrier mobility of up to 9000 cm 2 V -1 s -1 is observed for the BLG films grown on h-BN/Pt foils under ambient conditions. We also propose a plausible growth mechanism of BLG growth on h-BN/Pt foils. Our findings will contribute for the better understanding of the fundamental BLG physics and the development of BLG-based devices.

Adsorption-induced change of carrier density is presently dominating inorganic semiconductor gas sensing, which is usually operated at a high temperature. Besides carrier density, other carrier characteristics might also play a critical role in gas sensing. Here, we show that carrier mobility can be an efficient parameter to dominate gas sensing, by which room-temperature gas sensing of inorganic semiconductors is realized via a carrier mobility-dominated gas-sensing (CMDGS) mode. To demonstrate CMDGS, we design and prepare a gas sensor based on a regular array of SnO 2 nanorods on a bottom film. It is found that the key for determining the gas-sensing mode is adjusting the length of the arrayed nanorods. With the change in the nanorod length from 340 to 40 nm, the gas-sensing behavior changes from the conventional carrier-density mode to a complete carrier-mobility mode. Moreover, compared to the carrier density-dominating gas sensing, the proposed CMDGS mode enhances the sensor sensitivity. CMDGS proves to be an emerging gas-sensing mode for designing inorganic semiconductor gas sensors with high performances at room temperature.

We report high-performance top-gate bottom-contact flexible polymer field-effect transistors (FETs) fabricated by flow-coating diketopyrrolopyrrole (DPP)-based and naphthalene diimide (NDI)-based polymers (P(DPP2DT-T2), P(DPP2DT-TT), P(DPP2DT-DTT), P(NDI2OD-T2), P(NDI2OD-F2T2), and P(NDI2OD-Se2)) as semiconducting channel materials. All of the polymers displayed good FET characteristics with on/off current ratios exceeding 10 7 . The highest hole mobility of 1.51 cm 2 V -1 s -1 and the highest electron mobility of 0.85 cm 2 V -1 s -1 were obtained from the P(DPP2DT-T2) and P(NDI2OD-Se2) polymer FETs, respectively. The impacts of the polymer structures on the FET performance are well-explained by the interplay between the crystallinity, the tendency of the polymer backbone to adopt an edge-on orientation, and the interconnectivity of polymer fibrils in the film state. Additionally, we demonstrated that all of the flexible polymer-based FETs were highly resistant to tensile stress, with negligible changes in their carrier mobilities and on/off ratios after a bending test. Conclusively, these high-performance, flexible, and durable FETs demonstrate the potential of semiconducting conjugated polymers for use in flexible electronic applications.

Black phosphorus is a promising candidate for future nanoelectronics with a moderate electronic band gap and a high carrier mobility. Introducing the magnetism into black phosphorus will widely expand its application scope and may present a bright prospect in spintronic nanodevices. Here, we report our first-principles calculations of spin-polarized electronic structure of monolayer black phosphorus (phosphorene) adsorbed on a magnetic europium oxide (EuO) substrate. Effective spin injection into the phosphorene is realized by means of interaction with the nearby EuO(111) surface, i.e., proximity effect, which results in spin-polarized electrons in the 3p orbitals of phosphorene, with the spin polarization at Fermi level beyond 30%, together with an exchange-splitting energy of ∼0.184 eV for conduction-band minimum of the adsorbed phosphorene corresponding to an energy region where only one spin channel is conductive. The energy region of these exchange-splitting and spin-polarized band gaps of the adsorbed phosphorene can be effectively modulated by in-plane strain. Intrinsically high and anisotropic carrier mobilities at the conduction-band minimum of the phosphorene also become spin-polarized mainly due to spin polarization of deformation potentials and are not depressed significantly after the adsorption. These extraordinary properties would endow black phosphorus with great potentials in the future spintronic nanodevices.

High carrier mobilities have recently been achieved in polymer field effect transistors (FETs). However, many of these polymer FET devices require the use of chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (DCB) during fabrication. The use of these solvents is highly restricted in industry because of health and environmental issues. Here, we report the synthesis of a low band gap (1.43 eV, 870 nm) semiconducting polymer (PDPP2DT-F2T2) having a planar geometry, which can be readily processable with nonchlorinated solvents such as toluene (TOL), o-xylene (XY), and 1,2,4-trimethylbenzene (TMB). We performed structural characterization of PDPP2DT-F2T2 films prepared from different solvents, and the electrical properties of the films were measured in the context of FETs. The devices exhibited an ambipolar behavior with hole dominant transport. Hole mobilities increased with increasing boiling point (bp) of the nonchlorinated solvents: 0.03, 0.05, and 0.10 cm 2 V -1 s -1 for devices processed using TOL, XY, and TMB, respectively. Thermal annealing further improved the FET performance. TMB-based polymer FETs annealed at 200 °C yielded a maximum hole mobility of 1.28 cm 2 V -1 s -1 , which is far higher than the 0.43 cm 2 V -1 s -1 obtained from the CF-based device. This enhancement was attributed to increased interchain interactions as well as improved long-range interconnection between fibrous domains. Moreover, all of the nonchlorinated solutions generated purely edge-on orientations of the polymer chains, which is highly beneficial for carrier transport in FET devices. Furthermore, we fabricated an array of flexible TMB-processed PDPP2DT-F2T2 FETs on the plastic PEN substrates. These devices demonstrated excellent carrier mobilities and negligible degradation after 300 bending cycles. Overall, we demonstrated that the organized assembly of polymer chains can be achieved by slow drying using high bp nonchlorinated solvents and a post thermal treatment. Furthermore, we showed that polymer FETs processed using high bp nonhalogenated solvents may outperform those processed using halogenated solvents.

In this Article, low-bandgap pTTDPP-BT polymers based on electron-accepting pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) and benzothiadiazole (BT) and electron-donating thienothiophene (TT) moieties were synthesized. Phototransistors have been fabricated using ambipolar-behaving pTTDPP-BT polymers as active channel materials. The electrical and photoresponsive properties of the pTTDPP-BT phototransistors were strongly dependent on the film annealing temperature. As-spun pTTDPP-BT phototransistors exhibited a low hole mobility of 0.007 cm 2 /(V·s) and a low electron mobility of 0.005 cm 2 /(V·s), which resulted in low photocurrent detection due to the limited transport of the charge carriers. Thermal treatment of the polymer thin films led to a significant enhancement in the carrier mobilities (hole and electron mobilities of 0.066 and 0.115 cm 2 /(V·s), respectively, for 200 °C annealing) and thus significantly improved photoresponsive properties. The 200 °C-annealed phototransistors showed a wide-range wavelength (405-850 nm) of photoresponse, and a high photocurrent/dark-current ratio of 150 with a fast photoswitching speed of less than 100 ms. This work demonstrates that a dual acceptor-containing low band gap polymer can be an important class of material in broadband photoresponsive transistors, and the crystallinity of the semiconducting polymer layer has a significant effect on the photoresponse characteristics.

Good electronic transport capacity and low lattice thermal conductivity are beneficial for thermoelectric applications. In this study, the potential use as a thermoelectric material for the recently synthesized two-dimensional TiS 3 monolayer is explored by applying first-principles method combined with Boltzmann transport theory. Our work demonstrates that carrier transport in the TiS 3 sheet is orientation-dependent, caused by the difference in charge density distribution at band edges. Due to a variety of Ti-S bonds with longer lengths, we find that the TiS 3 monolayer shows thermal conductivity much lower compared with that of transition-metal dichalcogenides such as MoS 2 . Combined with a high power factor along the y-direction, a considerable n-type ZT value (3.1) can be achieved at moderate carrier concentration, suggesting that the TiS 3 monolayer is a good candidate for thermoelectric applications.

PbI 2 -enriched mixed perovskite film [FA 0.81 MA 0.15 Pb(I 0.836 Br 0.15 ) 3 ] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FA 0.81 MA 0.15 Pb(I 0.836 Br 0.15 ) 3 film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state. PSCs are fabricated with this mixed perovskite film, but a significant electron transport barrier at the TiO 2 -perovskite interface limited their performance. Cs 2 CO 3 and CsI are then utilized as functional enhancers with which to substantially balance the electron and hole transport and increase the carriers (both electrons and holes) mobilities in PSCs, resulting in much-improved solar-cell performance. The modified PSCs exhibit reproducible power conversion efficiency (PCE) values with little hysteresis effect in the J-V curves, achieving PCEs up to 19.5% for the Cs 2 CO 3 -modified PSC and 20.6% when subsequently further doped with CsI.

Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude. We extract the carrier density, carrier mobility, and Seebeck coefficient at different doping levels to obtain a clear image of carrier-transport mechanisms. This approach not only leads to a better understanding of the physical properties of the conducting polymer but also is useful for developing applications requiring patterned, large-area conducting polymers.