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Organic semiconductors (OSCs) possess diverse chemical structures and tailored optoelectronic properties via simple chemical modifications, so increasing use of them are found in efficient visible-light photocatalysis. However, the weak chemical bonds and the poor charge behavior (e.g., low concentration of free charge carriers, low carrier mobility) intrinsic in them, always incur quite limited stability and efficiency. Therefore, the assembly of them into refined nanostructures or nanocomposites is usually proposed to enhance their optoelectronic properties, as well as the photocatalytic efficiency and reliability. Zero-dimensional (0D) nanoparticles are low in size and hence high specific surface area (SSA); One-dimensional (1D) nanostructures are usually arranged in an orderly long range thus leading to low surface defect density and increased carrier mobility; Two-dimensional (2D) nanostructures are particularly capable of enhancing the photogenerated charge utilization because of their large reaction sites and shortened charge transport length. Furthermore, the building of heterogeneous interfaces in the nanocomposites can effectively facilitate the special charge separation. All these highlight the importance of organic nanostructures in improving the photocatalytic activity and stability. Therefore, organic semiconductor nanostructures (OSNs) have been increasingly used in the photocatalytic water splitting into H2 and O2, CO2 reduction, pollutant decomposition, disinfection, and etc.. In this review, we first examine the important optoelectronic properties of OSNs that govern the photocatalytic processes; we then analyze different classes of OSNs and their mechanistic pathways, with an emphasis on the structure-property relationships; we also introduced various photocatalytic applications of OSNs; we lastly propose the challenges and future outlook in real use.

Semiconductor electrocatalysis with weak conductivity can accumulate extremely high carriers at semiconductor-electrolyte interface by self-gating effect, which strongly promotes electrocatalytic efficiency. The correlation between semiconductor carrier mobility and electrocatalysis performance is still unclear. Herein atomic-thin transition metal dichalcogenides based composites have been developed for hydrogen evolution reaction (HER) performed with on-chip microdevices. Electrical and electrochemical measurement of individual flack verified the key role of high carrier mobility for enhanced HER activity. Carrier mobility regulation further demonstrated its high dependence with HER performance under self-gating. Our study provides new insight into the carrier mobility of the semiconductor in the electrocatalysis, paving the way for designing high-performance semiconductor catalysts.

Perovskite solar cell (PSC) has gradually shown its great superiority in photovoltaic filed to compete commercial solar cells owing to its great advantages, such as high efficiency and low fabrication cost. On the way towards commercialization, great efforts have been achieved by accelerating charge extraction and reducing carrier recombination. Recently, two-dimensional (2D) layered materials have attracted increasing interests for application in PSCs due to their distinctive chemical and physical properties, such as high carrier mobility and tunable bandgap, which greatly determines the perovskite film growth kinetics, carrier transfer and stability of PSCs. Therefore, with the aim to better understand their recent development and application in PSC, in this review, the emerging 2D materials beyond graphene as charge transport layers, buffer layers and additives in perovskite film for enhancing the efficiency and stability of PSCs are summarized. However, there are still some crucial challenges to be addressed for commercialization. Finally, the challenges and prospects of these 2D nanomaterials for application in PSCs are further proposed for future development.

Semiconductor-based photocatalytic and photoelectrochemical (PEC) processes can convert solar energy into high-density chemical energy or for the treatment of environmental pollutants, which are ideal ways to deal with environmental and energy crises. The development of high-efficiency photocatalysts and photoelectrodes is the key to the in-depth development and practical application of the two technologies. Black phosphorus (BP) has excellent physicalcochemical properties such as adjustable band gap, high carrier mobility, large specific surface area and anisotropy, making it one of the most promising catalysts. BP-based heterostructure can not only realize the effective separation of photogenerated carriers but also improve the stability of BP, and is widely used in photocatalytic and PEC reactions. In this review, we first introduce the crystal structure, band structure, anisotropy, and preparation of BP with different dimensions (bulk, zero-dimension and two-dimension). Then, according to the transfer path of the photogenerated carriers and the components, the BP-based heterostructures are divided into type I heterojunction, type II heterojunction, Z-scheme heterojunction, S-scheme heterojunction, BP/carbon-based material heterostructure, BP/metal heterostructure and multi-component heterostructure. Highlighted are the diverse photocatalytic applications of BP-based heterostructure, such as water splitting and CO2 reduction, N2 fixation, pollutant degradation, photothermal and photodynamic therapy. Finally, some concluding views and opinions are stated on the challenges and opportunities faced by the further development of BP-based heterostructures in photocatalysis and PEC water splitting.

Today, the earnest need for earth-abundant and environmentally friendly thermoelectric materials has revealed the importance of semiconductor metal oxides in order to eliminate the barrier towards their wide-ranging use in industrial applications. In the present work, we demonstrate the synthesis of p-type tin oxide thin films on quartz glass and Si substrates by using electron beam evaporation technique followed by rapid thermal annealing process at 200 °C for 20 min in Ar-atmosphere. Annealing-induced structural, electrical, optical and thermoelectric properties of pristine and annealed SnO thin films are primarily studied. The compositional and structural analysis of SnO films are performed by using X-Ray Diffraction, Scanning Electron Microscope as well as Atomic Force Microscope. Moreover, the mechanism of thermoelectric transportation at different measurement temperatures is deeply inspected via thermoelectric measurements. The Seebeck coefficient, carrier concentration and hole mobility in conjunction with the development of thin film nanostructures are discussed, predominantly. The optimal annealing may tune structural, electro-optic and thermoelectric properties of SnO films for the commercial-level maturity of thermoelectric devices for energy applications.

All-inorganic Cs3Bi2I9 (CBI) halide perovskites are sought to be candidate for photoelectrical materials because of their low toxicity and satisfactory stability. Unfortunately, the discrete molecular [Bi2I9]3− clusters limit the charge-transport behaviors. Herein, the defect halide perovskite based on trivalent Bi3+ is expanded to Cs3Bi2I6Br3 (CBIB). Centimeter-size CBIB single crystal (Φ 15 × 70 mm3) was grown by the vertical Bridgeman method. The powder X-ray diffraction analysis shows that CBIB has P 3 ¯ m 1 structure with lattice parameters of a = b = 8.223 A, c = 10.024 A, α = β = 90° and γ = 120°. The density functional theory (DFT) calculations demonstrate that the charge density distribution was enhanced after the dimensional expansion. The enhancement of carrier transport ability of (00l) in-plane is characterized before and after dimensional improvement. The obtained CBIB(001) exhibited an electron mobility up to 40.03 cm2 V−1 s−1 by time-of-flight (TOF) technique, higher than 26.46 cm2 V−1 s−1 of CBI(001). Furthermore, the X-ray sensitivity increases from 707.81 μC Gy−1 cm−2 for CBI(001) to 3194.59 μC Gy−1 cm−2 for CBIB(001). This research will deepen our understanding of Bi-based perovskite materials and afford more promising strategies for lead-free perovskite optoelectronic devices modification.

The SrTiO3 perovskites n-doped with Sm3+, Dy3+, and Nb5+ were prepared via the conventional solid state reaction route (SSR) followed by spark plasma sintering (SPS) process. The SPS in dynamic vacuum promotes formation of Ti3+ and Nb4+ species, as verified by the XPS analysis. Presence of the reduced cations, primarily Ti3+, is in agreement with the observed color changes and enhanced electrical conductivity of the samples. The Sr-site substitution by Sm and Dy is highly effective in phonon scattering and reducing the lattice thermal conductivity. Besides, this substitution significantly increases the electron mobility and electrical conductivity, by reducing the lattice strain imposed by the Ti/Nb substitution. Thermoelectric measurements indicated that a doubly doped sample with the Sr0.95Sm0.05Ti0.9Nb0.1O3 loading chemical composition reached the figure of merit (zT) value of 0.41 at 873 K. Such a high zT value originates primarily from a high carrier mobility of 24 cm2/V s and a low thermal conductivity of 2.4 W/m K.

We investigated the optical and electrical properties of Ta2O5/Ag/Ta2O5 films as functions of the thicknesses of the Ta2O5 and Ag layers. It was found that with an increase in the thicknesses of the Ta2O5 and Ag layers from 10 to 40 nm and from 12 to 24 nm, respectively, the sheet resistance, carrier concentration, electron mobility, and resistivity of the Ta2O5/Ag/Ta2O5 film varied from 2.02 to 8.95 Ω/sq, 5.74 × 1021 to 2.92 × 1022 cm–3, from 13.21 to 24.07 cm2/V·s, and from 8.89 × 10-6 to 8.24 × 10-5 Ω cm, respectively. The average transmittance (Tav) of the multilayer samples ranged from 57.18% to 93.99%, and it depended on the Ta2O5 and Ag layer thicknesses. The highest Tav of 93.99% was observed for the film with 35 nm thick Ta2O5 and 18 nm thick Ag layers, and the peak Haacke's figure of merit (157.04 × 10–3 Ω–1) was obtained for 20 nm thick Ta2O5 and 21 nm thick Ag layers. Ta2O5 (100 nm) and Ta2O5/Ag/Ta2O5 (20 nm/21 nm/20 nm) samples had optical bandgaps of 4.70 and 4.45 eV, respectively. Film Wizard simulations were conducted to understand the dependence of the transmittance of the multilayer on the thicknesses of the Ta2O5 and Ag layers, and phasor analyses were performed to determine how the transmittance of the Ta2O5/Ag/Ta2O5 (20 nm/21 nm/20 nm) film depended on the Ta2O5 layer's thickness.

Alloying with Se is proved to be feasible to suppress the lattice thermal conductivity (κL) of tellurium by introducing multidimensional lattice defects. However, extra ionization impurity centers induced by Se alloying are harmful to the electric transport properties of the matrix. In this paper, we propose that the incorporation of Ag could successfully compensate the lost carrier mobility (μH) due to Se alloying through the regulation of microstructure, resulting in the higher power factor (PF) than that of samples without Ag. After composition optimization, the κL decreased from 1.29 W m−1 K−1 of Te0.99Sb0.01 to 1.05 W m−1 K−1 of Te0.94Ag0.02Se0.03Sb0.01 at 350 K, while the PF remained unchanged or even slightly increased. Benefit from the synergistic effect of carrier mobility compensation and phonon scattering, a maximum zT of 0.91 at 573 K and an average zT of 0.57 (between 298 and 573 K) are achieved in Te0.94Ag0.02Se0.03Sb0.01. This work presents a new strategy for decoupling the thermal and electric parameters of Te-based thermoelectric materials.

The study of valence fluctuation is made on TmSe compound from simulated theoretical x-ray powder diffraction data. The theoretical lattice parameter is in agreement with experimental parameter. The amount of charge transfer is deduced as 0.23ē which proves the presence of intermediate valence fluctuation in the system. Further a theoretical Study is made on TmSe1−xTex (x = 0.5, 0.77, 0.83 and 1.00) to deduce electrical transport properties by using only two parameters, lattice constant and energy gap. The calculated transport properties electrical resistivity, carrier mobility, carrier concentration, carrier effective mass and dielectric constant are compared with the available experimental data which agrees with each other.

Graphene-based 2D materials have shown extraordinary promise in electrochemical energy storage, owing to their high electrochemical activity, fast carrier mobility, and large electronic conductivity. However, low specific capacity ( 5 mAh cm−2). The highly interpenetrating graphene oxide network in the HAGO/Co@CN electrode accelerates electronic transport. In addition, benefiting from the advanced layered architecture, the HAGO/Co@CN electrode exhibits excellent structural stability and thickness-independent electrochemical performances. By systematically adjusting the orientation of GO/Co@CN nanosheets inside electrode to optimize the electron/ion transmission to deliver high areal capacity and high-rate capability at high mass loading. More importantly, a designed full cell with NCM622 cathode and HAGO/Co@CN anode shows ultrahigh capacity retention of >98% at 1 C after 500 cycles with a commercial-level reversible capacity of 2.3 mAh cm−2.

Understanding the structure–property relationships in antiaromatic molecules is crucial for controlling their electronic properties and designing new organic optoelectronic materials. Here we report the design, synthesis, and characterization of three new antiaromatic molecules (Pn, n = 1–4) based on the pentalene (P) antiaromatic core, to investigate how electron-donating and electron-accepting substituents affect P1–P4 properties. As expected, the optical, HOMO and LUMO energy levels and electronic structure are greatly modulated by core substitution. Compared to the unsubstituted compound (P1), P3 and P4 containing strong electron-withdrawing units reduced antiaromaticity as assessed by nucleus-independent chemical shift (NICS) calculations compared with P2, which is functionalized with strong electron-donating units, showing that substitution strongly tunes local antiaromaticity. Organic field-effect transistors (OFETs) fabricated using these materials indicate that P2 has an average hole mobility of ∼10−4 cm2 V−1 s−1 while P3 has an average electron mobility of up to 0.03 cm2 V−1 s−1, versus FET-inactive P1. Therefore, introduction of strong π-extended electron-withdrawing or electron-donating substituents onto an antiaromatic core is an effective strategy to switch-on charge transport capacity.

Two conjugated polymers (CPs) Fu-F and Fu-Cl that are soluble in a green solvent anisole were successfully synthesized via direct arylation polycondensation (DArP) using a furan-flanked diketopyrrolopyrrole (DPP) derivative (FDPP-Br) as the C–Br monomer and (E)-1,2-bis(3,4-difluorothien-2-yl)ethene (4FTVT) or (E)-1,2-bis(3,4-dichlorothien-2-yl)ethene (4ClTVT) as the C–H monomer. With anisole as the processing solvent and polyethylenimine ethoxylated (PEIE) as the electrode modification layer, n-type organic thin-film transistors (OTFTs) of the polymers were fabricated via bar-coating. The electron mobility (μe) of the devices based on Fu-Cl was only in the magnitude of 10−2 cm2 V−1 s−1, owing to the unfavoured fine granular film morphology. In contrast, Fu-F films showed fibre-like morphology with the polymer chains aligned along the bar-coating direction, which is favourable for the charge transport in OTFTs. Therefore, Fu-F delivered much better device performance with the μe of up to 2.79 cm2 V−1 s−1. Our study demonstrates that green solvent processed high mobility CPs can be synthesized by DArP, an emerging eco-friendly protocol for the synthesis of CPs.

SnS2 with atomic thickness has attracted extensive attention in the field of photocatalysis due to its special physicochemical properties, suitable band gap, low cost and low environmental toxicity. However, the application of SnS2 in the field of optoelectronics is restricted by its low photocatalytic efficiency and carrier mobility. In this study, vacancy and transition metal atoms are introduced into SnS2 monolayer to modulate its physicochemical properties. Meanwhile, the SnS2 monolayer modified by vacancy and transition metal atoms is combined with graphene to form a heterostructure, which promotes the separation of photogenerated electron hole pairs. The results of theoretical calculation show that SnS2/graphene heterojunction can promote the separation of photogenerated carriers in intrinsic monolayer SnS2, improve the photocatalytic efficiency and carrier mobility. The modification of Sn vacancy and Fe, Co atoms not only expands the visible light response range of SnS2/graphene heterojunction, but also introduces magnetism, which is expected to be applied in spin optoelectronic materials. In this work, defects, doping and heterojunction assembly are rationally integrated, which provides a new idea for the design and development of spin optoelectronic devices based on monolayer SnS2.

As the sandwiched hole transporting materials (HTMs) layers are in direct contact with up-coated perovskite layer and bottom electrode in p-i-n structured perovskite (i-PSCs), the film quality of HTMs determines the morphological properties of the perovskite absorbent. To achieve excellent surface morphology of HTM films, two asymmetric structured HTMs, which featuring with methoxytriphenylamine electron donor and imidazole core, has been successfully developed through two simple reactions of cyclization and Buchwald-Hartwing coupling. The DI-TPA was designed by incorporating an extra methoxytriphenylamine unit in the C2 site of imidazole core, whereas an isolated benzene ring was introduced for DI-Ar. The asymmetrical conformation contributes to high glass transition temperatures and supports thermal-stable amorphous properties in both HTM films. Comparing with DI-Ar, DI-TPA featuring with extended backbone realizes more effective capability of hole extraction arising from the enhanced intermolecular - interaction in the solid state. Consequently, the i-PSCs with DI-TPA as dopant-free HTM generates an encouraging power conversion efficiency of 16.54%, significantly exceeding that with DI-Ar (13.77%). Noted that the efficiency is shown to outperform that of commercial dopant-free HTM PEDOT:PSS (13.41%) under the same condition. This work offers a fundamental strategy by reinforcing electron-donation to improve the hole mobility of asymmetric HTMs for dopant-free p-i-n structured inverted PSCs.

Transparent-flexible thermoelectric materials are attractive for future small-sized consumer electronics, the internet of things, and wearable devices. The microstructural evolution and subsequent thermoelectric properties of Ti 1%.at-doped ZnO thin films, grown on polyimide flexible substrates, are presented. The thin films were grown using radio frequency a magnetron sputtering method followed by annealing for 60 min at temperatures of 200–400 °C under vacuum atmosphere. Post-annealed films demonstrate a hexagonal Wurtize structure. It is found that the annealing helped to relax residual stresses in the thin films, subsequently leading to enhanced charge concentration, carrier mobility, mean free path, and density-of-states effective mass. The thin film, annealed at 300 °C, illustrates the highest power factor of the films measured at room temperature at 19.10 μW m−1 K−2. Further increases in the annealing temperature suggest Ti2+ diffuses into the ZnO lattice and in turn disturbs the crystalline structure; this results in a reduction of the power factor to 9.32 μW m−1 K−2 at an annealing temperature of 350 °C.

This paper distinguished hydrogen roles to improve electron mobility and carrier concentration in ZnO and Al doped ZnO sputtered films. By combining experimental evidences and theoretical results, we find out that hydrogen located at oxygen vacancy sites (HO) is the main factor gives rise to increase simultaneously mobility and carrier concentration which has not been mentioned before. Introducing appropriate hydrogen content during sputtering not only results in crystalline relaxation but also supports doping Al into ZnO, increasing carrier concentration and electron mobility in the film. First principles calculations confirmed hydrogen substitutional stability for oxygen vacancy, significantly reducing electron conductivity effective mass and hence increasing electron mobility. In particular, 0.8% hydrogen partial pressure ratio achieved 61 cm2V−1s−1 maximum electron mobility, optical transmittance above 82% in visible and near-infrared regions, and 2 × 1020 cm−3 carrier concentrations for H Al co-doped ZnO film. These values approach ideal electrical and optical properties for transparent conducting oxide films. The presence of one maximum electron mobility was attributed to competition between increasing mobility due to restoring effective electron mass and hydrogen passivation of native defects, and decreased electron mobility due to electron-phonon scattering.

In this letter, we comprehensively investigate the electrical properties of the 1200 V planner-gate 4H-SiC power metal–oxide–semiconductor field-effect transistors under the mechanical strains. Three kinds of strains, including the biaxial strain, uniaxial strain parallel to the gate channel, and uniaxial strain perpendicular to the gate channel, are applied using the wafer bending system. It is found that all kinds of compressive strains improve the drain current ( Id ) under the same gate voltage ( Vg ) and shift the threshold voltage ( V th) negatively, while the tensile strains decrease Id and shift V th positively. The V th shift mainly results from the strain modulated band structure in the poly-Si gate. Under the same overdrive gate voltage ( V ov), biaxial strains merely change Id , while both the parallel and perpendicular uniaxial compressive strains enhance Id . The uniaxial compressive strain elevates the electron mobility in the inverted channel by repopulating more electrons into the valleys with a smaller conduction effective mass, which results in the current improvement.

In this work, we demonstrated that the co-crystallization strategy has offered an efficient and promising alternative route to achieve high-performance n-type semiconductors through charge-transport switching from pristine p-type systems. By using a simple “green synthesis” process through molecular “doping” with F4TCNQ into a p-type planar azaacene derivative TMIQ (0.27 cm2 V−1 s−1) host, charge transport characteristic switching occurs with a high electron mobility of 0.12 cm2 V−1 s−1 under atmospheric conditions obtained for the D–A complex TMF4TQ (cocrystal). The reasons for such switching lie in the ingenious energy level and molecular packing arrangement tailoring. Specifically, the insertion of F4TCNQ molecules has led to packing transformation from herringbone stacking (TMIQ) to a dense 2D brick arrangement and the low-lying LUMO levels (−4.55 eV) aligned to gold electrodes, thereby facilitating efficient electron injection and transport, and ensuring the air-stable nature, which is further confirmed using theoretical calculations. We believe that our work would provide new insights into high-performance air-stable n-type organic semiconductors exploration.

5,15-Bis(triisopropylsilyl)ethynyltetrabenzoporphyrin (TIPS-H2BP) gave a one-dimensionally extended columnar packing motif. The single crystal field-effect transistor of TIPS-H2BP exhibited clearly better hole mobility (2.16 cm2 V−1 s−1) than its metal complexes (ca. 0.1 cm2 V−1 s−1), with efficient charge transport through π–π stacking along the tetrabenzoporphyrin units.

The phonon dispersion and optical properties of mechanically exfoliated SnSSe are investigated with the aid of high resolution Raman scattering and photoluminescence (PL) spectroscopies along with first principle calculations. The Raman modes indicates two-fold symmetry for in-plane vibrations and four fold symmetry for out of plane vibrations. Consequently, the different polarization properties of phonon modes demonstrate the anisotropic nature of SnSSe. The softening of Raman modes with increasing temperature is described in terms of thermal expansion and anharmonic scattering which contributes to phonon vibration, whereas a weak interlayer interaction in SnSSe layers is observed. The significant suppression of PL signal at higher temperature is related to the increase of the non-radiative recombinations of the electron-hole pairs, as a result of increment in the number of phonons and in the thermal excitations of carriers. In addition, the fabricated electrical device on few layers SnSSe shows a significant ION/IOFF ratio and good electron mobility for optoelectronic applications. These results further provide the microscopic understanding of SnSSe as an important material, which have better insights to control phonon propagation in thermoelectric, photovoltaics, and other materials to induce thermal management

Rational functionalization plays an important role to push forward graphene applications in multifarious cutting-edge technologies. A key topic that how to program the regular distribution of functional groups, however, remains a big challenge. Herein, we developed a very simple, high-throughput graphite reduction methodology to attain the negatively-charged graphene which carried ultrahigh-density and evenly-distributed negative charges. Guided by these negative charges, electrophiles were regularly attached to graphene sheets. On the other hand, potassium reduction will not break the carbon-carbon σ-bonds, hence graphene hexagonal lattice was kept as perfect as the pristine pattern. Structural advantages of the negatively-charged graphene derivatives allowed a far more excellent conductivity and electron mobility than the counterparts derived from the prevalent graphene oxide precursor.

CsxWO3 nanocrystals which exhibit localized surface plasmon resonance (LSPR) and small polaron transfer in wavelength of the near-infrared radiation have attracted great attention to fabricate the spectrally selective coating. Enhancing the LSPR and small polaron transfer of CsxWO3 nanocrystals is effectively achieved by introducing aliovalent dopant into its empty trigonal tunnels of the crystal lattice, but the lack of controllable synthesis process reserves some essential issues unanswered with respect to the effects of the dopant concentration on absorption coefficient, free carrier density and carrier mobility. Herein, Li-doped CsxWO3 nanocrystals were successfully prepared with the highest reported absorption coefficient, which demonstrated stronger absorption performance than the CsxWO3 nanocrystals without Li doping. The introduction of lithium into the crystal structure as a cation dopant can enhance the free carrier density of the nanocrystals, which leads to a higher absorption coefficient. The absorption coefficient variation of LSPR and small polaron transfer of Li-doped CsxWO3 nanocrystals was explained by the free carrier density and carrier mobility. This doping strategy allows CsxWO3 nanocrystals to become spectrally tunable within the wavelength of near-infrared radiation. When the Li/W molar ratio was 0.4, the free carrier density reached 10.22 × 1014 cm−3. The spectrally selective coating prepared by Li-doped CsxWO3 nanocrystals displayed excellent spectral selectivity with TVis, TNIR, Tlum, and Tsol of 68.79 %, 9.17 %, 72.61 % and 47.95 %, respectively. This doping strategy provides a promising potential to improve the spectral tunability of CsxWO3 nanocrystals for the practical application of energy-saving windows.

Two-dimensional (2D) materials have received extensive attention in the fields of electronics, optoelectronics, and magnetic devices attributed to their unique electronic structures and physical properties. The application of strain is a simple and effective strategy to change the lattice structure of 2D materials thus modulating their physical properties, which further facilitate their applications in carrier mobility transistor, magnetic sensor, single-photon emitter etc. In this short review, we focus on the strain applied via substrate engineering. Firstly, the relationship between the strain and physical properties has been summarized. Secondly, the methods for achieving substrate engineering-induced strain have been demonstrated. Finally, the latest applications of strained 2D materials have been introduced. In addition, the future challenges and development prospects of strain-modulated 2D materials have also been proposed.

Graphene, a two-dimensional (2D) carbon material that has a zero bandgap with a symmetric band structure, has drawn extensive attention, owing to its exceptional electrical, mechanical, thermal and electron mobility properties. However, 2D graphene sheets encounter an aggregation and restacking issues, which affect the electron transport and charge separation. Therefore, a three-dimensional (3D) graphene structure has been explored to address these problems. The fabrication of 3D graphene via chemical vapor deposition (CVD) has intrigued comprehensive attention in photoelectrochemical (PEC) water splitting. It can produce high-quality graphene with a minimal defects of 3D graphene structures that can exhibit an outstanding performance for PEC water splitting. In this study, we investigated the effect of annealing time during CVD growth of 3D graphene/nickel (Ni) foam where the Ni foam was annealed with various annealing times (20–60 min). The coverage area of graphene on Ni foam has improved, based on characterization using field emission scanning electron microscope (FESEM). Raman and EDX analysis further confirmed the presence of graphene layer on Ni foam. The optimum annealing time was obtained at 50 min. The sample was tested for PEC water splitting and the current performance for 50 min annealing sample was found higher than the pure Ni foam, 596.46 mA and 429.33 mA, respectively. Thus, improved coverage area of graphene on Ni foam resulted in higher generated current that has a potential for PEC water splitting.

Through the introduction of two perylene diimide (PDI) moieties to the triphenylamine (TPA) core, a PDI dimer-based electron transport material has been synthesized with an A (electron acceptor)–D (electron donor)–A structure. It demonstrated a high electron mobility of 8.23 × 10−4 cm2 V−1 s−1 as a thin film and achieved a PCE of 20.07% in perovskite solar cells, higher than that of PC61BM (18.38%) as the standard reference under the same conditions. This is the highest conversion efficiency among various PDI derivatives as ETMs, providing the optimized molecular configuration by combination of twisted core (TPA) and planar peripheral moieties (PDI), as well as matched electronic properties with multiple charge transfer processes.

We present results from a characterisation of bulk defects in CdTe wafers, and their role in the degradation of charge transport performance of CdTe radiation detectors. Sub-bandgap IR microscopy and X-ray Lang topography have been used to characterise material quality prior to device processing. IR microscopy clearly identifies extended defects such as tellurium precipitates in the material bulk, whilst Lang topography characterises stacking faults, crystallite boundaries and other crystallographic features in the near-surface region. After fabrication of contacts onto the material, ion beam induced charge imaging is used to investigate the correlations between material defects and charge transport. Digital ion beam induced charge imaging is used to produce high resolution maps of charge signal amplitude, carrier drift time, and carrier drift mobility.

Compared to epitaxial gallium arsenide (GaAs) grown at regular temperature, low-temperature epitaxial growth of GaAs results in a dramatically shorter carrier lifetime. This produces subpicosecond device responses and enables ultra-high-speed photodetection. However, low-temperature-grown GaAs (LT-GaAs) photodetectors usually exhibit poor responsivity due to the lower carrier mobility in LT-GaAs. Here, the properties and characteristics of the low-temperature-grown material are investigated. Carrier lifetime as a function of growth and annealing temperatures are explored as well as nonlinear optical characteristics and optical absorption well below the bandgap energy of GaAs. Several photodetector styles (photoconductive, PIN, MSM, and waveguide photodetectors) utilizing LT-GaAs are presented. These photodetectors enable a variety of high-speed photonic systems. Their technology and the future use of LT-GaAs are explored, especially in the field of THz emitters and receivers.

Cu2O is a promising p-type semiconductor for low-cost photovoltaics and transparent optoelectronics. However, low-cost and low-temperature fabrication of Cu2O films with good transport properties remains challenging, thus limiting their widespread adoption in devices. Here, we report Cu2O thin films of 20–80 nm thickness with hole mobility up to 92 cm2V−1s−1 using atmospheric-pressure spatial atomic layer deposition at temperatures below 260 °C, from a copper (I) hexafluoro-2,4-pentanedionate cyclooctadiene precursor. Raman spectroscopy indicates the presence of copper split vacancies and shows that the high hole mobility can be correlated to a low concentration of shallow acceptor defects. The optical bandgap of deposited films can be tuned between 2.08 eV and 2.5 eV, depending on the deposition temperature. All-oxide semitransparent Cu2O/ZnO solar harvesters are fabricated, showing efficiency values comparable to devices that incorporate much thicker Cu2O layers. Our work provides a promising approach towards cost-efficient, all-oxide solar harvesters, and for other (opto)electronic devices. Semiconducting Cu2O is attractive for photovoltaic and optoelectronic devices, though balancing high hole mobility with low-cost fabrication is challenging. Here, Cu2O thin films with high hole mobility of 92 cm²V−1s−1 are deposited in air, and applied in a semi-transparent solar harvester.

A facile solution process to synthesis ZnO thin films was successfully conducted in this work. Zinc acetate dihydrates were used as the main precursor, dissolved in the mixture of acetylacetone and ethanol whichact as solvent and precursor simultaneously. This mixture deposited by spin coating and dried under ambient atmosphere at room temperature. The reaction mechanism, structure, morphology, chemical composition and optoelectrical properties of the resulted ZnO thin film were studied. The as deposited films were annealed at 500 °C for 2 h under O2 gas flow added with H2O vapor and CO2 gas. The ZnO thin films showed a dense, homogenous morphology and high transparency. The film is an n-type semiconductor with 3.18 eV bandgap, has 1.25 × 10−19 cm3 carrier concentration, 12 cm2/Vs electron mobility and 2.42 × 10−3 Ω·cm resistivity making it suitable for application as window layer in a photovoltaic cell.

Summary Most organic/polymeric semiconductors are p-type semiconductors, whereas their n-type versions are limited in both availability and carrier mobility. How to develop high-rate n-type organic/polymeric semiconductors remains challenging. Here, we report an approach to high-rate n-type semiconductors via topology-directed polycondensation of conventional p-type knots with n-type isoindigo linkers to form non-conjugated tetragonal and hexagonal two-dimensional polymeric frameworks. The polymers are planar in conformation and show flattened frontier levels, which enable electrons to move along the non-conjugated polymeric backbones. The eclipsed face-to-face stack reduces reorganization energy and greatly strengthens electronic coupling, thus enabling band-like electron conduction perpendicular to polymer layers. A device recording electron mobility as high as 8.2 cm2 V−1 s−1 was achieved with Hall effect measurements, whereas time- and frequency-resolved terahertz spectroscopy revealed a benchmark mobility of 13.3 cm2 V−1 s−1. These new mechanistic insights with exceptional mobility open the way to high-rate n-type organic/polymeric semiconductors.

MoS2 thin film is deposited on ITO/CdS substrate by in-situ hydrothermal method, which is expected to be a potential absorber material for planar heterojunction solar cell due to its high absorber coefficient and carrier mobility. The CdS buffer layer provides a robust template for the quasi-epitaxial growth of MoS2 with (0 0 2) preferred orientation by enjoying the analogical hexagonal structures and the shared sulfur atoms, resulting in a benign interface of CdS/MoS2. Then a device with ITO/TiO2/CdS/MoS2/Carbon-Ag structure is assembled after coating carbon-Ag electrode. The effects of the growth characteristics, morphology changes and optical properties of MoS2 on the device performance are studied systematically. Finally, a primary efficiency of 0.12% is achieved using a P-type MoS2 absorber with a thickness of 305 nm, exhibiting an outstanding stability. The one-dimensional solar cell capacitance simulator (SCAPS) is further used to reveal the bottleneck of device performance. After optimizing the doping density (1 × 1015 cm−3) and defect density (

Nowadays, high-quality metal oxide thin film transistors grown by solution process have the most potential to replace the traditional a-Si TFT as the next generation of transparent electronics for various applications. However, the low intrinsic carrier concentration and poor charge carrier mobility of metal oxide thin film hinder its development. In order to solve these problems, the heterojunction structure was proposed. In this study, the Indium Oxide/Indium Gallium Oxide (In2O3/IGO) heterojunction was systematically investigated, and the existence of a two-dimensional electron gas was found. There is a large accumulation of carriers at the In2O3/IGO heterojunction interface, and the Hall tests show that the In2O3/IGO heterojunction has the highest carrier concentration of 7.82 × 1012 cm−2 and a carrier mobility of 10.22 cm2V−1s−1. This research can provide a theoretical guidance for promoting the development of oxide thin film transistor technology.

Heterostructures of quantum dots (QDs) and two-dimensional (2D) materials show promising potential for photodetection applications owing to their combination of high optical absorption and good in-plane carrier mobility. In this work, the performance of QD-2D photodetectors is tuned by band engineering. Devices are fabricated by coating MoS2 nanosheets with InP QDs, type-I core-shell InP/ZnS QDs, and type-II core-shell InP/CdS QDs. Comparative spectroscopic and photoelectric studies of different hybrids show that the energy band alignment and shell thickness can influence the efficiency of charge transfer (CT), energy transfer (ET), and defect-related processes between QDs and MoS2. Benefiting from efficient CT between the QDs and MoS2, a significant enhancement of responsivity and detectivity is observed in thick-shell InP/CdS QD-MoS2 devices. Our results demonstrate the feasibility of using core-shell QDs for regulating the ET and CT efficiency in heterostructures and highlight the importance of interface band design in QD-2D and other low-dimensional photodetectors.

The role of hole transport material (HTM) layer is critical to obtain high performances for perovskite solar cells (PSCs). The development of novel HTMs with good stability, low cost, and high hole mobility for PSCs is an essential research direction. Herein, new isoindigo-based HTMs were designed and investigated using density functional theory (DFT) computations combined with Einstein relation and Marcus theory. It was found that the energies of HOMO and LUMO levels were increased with an enhancement in the electron-donating character of substituents located on the diphenylamine moieties. The molecules with X = N(Me)2, NHMe, NH2, OMe, OH, and Me substituents exhibited appropriate energy level alignments with respect to MAPbI3, which indicated the hole could be injected from the MAPbI3 to the designed HTMs. Based on the solvation energies, the designed HTMs would be expected to be soluble in the dichloromethane solvent. The results of the absolute hardness and electrostatic surface potential calculations revealed that the stability of such HTMs was decreased with an increase in the electron-donating character of the substituents positioned onto the diphenylamine groups. All of the designed HTMs, except for the X = OH molecule, illustrated considerably greater hole mobility than that of the Spiro-OMeTAD. In view of the matched HOMO level, good hole mobility, plus acceptable solubility and stability, the designed isoindigo based HTMs would have the potential for replacing the Spiro-OMeTAD in PSCs.

Ag2Se is a narrow band gap n-type semiconductor with high carrier mobility and low lattice thermal conductivity. It has high thermoelectric performance near room temperature. However, there is a noticeable data discrepancy for thermoelectric performance in the reported literature studies, which greatly hinders the rational understanding and potential application of this material. In this work, we comprehensively studied the homogeneity, reproducibility, and thermal stability of bulk Ag2Se prepared by melting and mechanical alloying methods followed by spark plasma sintering. By virtue of the atom probe topology technique, we revealed nanosized Ag- or Se-rich precipitates and micropores with Se-aggregated interfaces that have not been detected previously. The samples prepared by melting and spark plasma sintering exhibit the best homogeneity and repeatability in thermoelectric properties despite abundant nanoprecipitates. Moreover, the thermoelectric performance of Ag2Se is greatly improved by introducing a slight amount of excess selenium. The average zT can steadily reach 0.8-0.9 in the range of 300-380 K, which is among the highest values reported for Ag2Se-based materials. This work will rationalize the evaluation of the thermoelectric performance of Ag2Se.

Although perovskite solar cells (PSCs) have made revolutionary progress in terms of power conversion efficiency (PCE), to achieve long-term stability and low-cost device manufacturing for commercialization of the devices, selection of proper hole transport layer (HTL) and affordable back contact are still crucial to realize the upscale manufacturing. However, the carbon-based perovskite still faces great challenges to further improve the device performance due to the low quality of the carbon/perovskite interface. Inorganic NiOx is a superior HTL candidate due to its favorable energy band alignment, superior chemical stability, high hole mobility, and low-cost manufacturing. To address the poor interface quality of the carbon-based PSCs, we report electrospun NiOx fibers as an effective HTL, resulting in highly efficient device performance of PCEs up to 13.73% when deployed in our carbon-based PSCs. NiOx has been introduced as an interfacial layer between the perovskite and the carbon counter electrode to study its impact on interfacial modification and device performance.

Photocatalytic splitting water is a promising method to obtain hydrogen energy. While design and synthesis of efficient and economical photocatalysts is one of the important contents. Janus MoSSe and WSSe monolayers are efficient and wide sunlight harvesting photocatalysts due to their intrinsic vertical electric fields. So how is the photocatalytic performance of lateral MoSSe∣WSSe heterojunctions, which possesses an intra-plane interface and intrinsic vertical electric field? In the present work, the structural property, electronic characteristic, optical property, and photocatalytic application of MoSSe∣WSSe lateral heterojunctions are systematically investigated. It is found that both zigzag and armchair configurations are semiconductors with suitable bandgaps of ∼ 1.60 eV. Besides, they possess a type-II band alignment where electrons tend to accumulate at the coupling interface of MoSSe side and holes at WSSe side, giving rise to a paralleled electric field in heterojunctions, which can largely promote the separation of photo-generated carriers. More remarkably, these heterojunctions exhibit pronounced solar-spectrum absorption efficiency, proper valence, and conduction band positions by initializing the redox reactions of H2O and high carrier mobility. Intriguingly, the zigzag MoSSe∣WSSe heterojunction has a better photocatalytic performance in an acidic environment, and the armchair MoSSe∣WSSe prefers to produce H2 and O2 in a neutral environment. These fascinating properties render the intra-plane MoSSe∣WSSe heterojunctions as the wide solar harvesting photocatalysts in further overall water splitting.

Thin-film transistor (TFT) applications of GeSn have attracted attention as a means of improving the performance of electronic devices. Based on our advanced solid-phase crystallization and TFT process technologies, we comprehensively studied the relationship between the film properties and TFT characteristics of polycrystalline GeSn. The initial Sn concentration ${x}_{\mathrm {i}}$ significantly changed the crystal and electrical properties of the GeSn layer. Excess Sn ( ${x}_{\mathrm {i}} \ge 4.5$ %) precipitated in GeSn and degraded its properties, whereas the appropriate amount of Sn effectively passivated defects in Ge and reduced the density of defect-induced acceptors and grain boundary traps while maintaining a high Hall hole mobility (>200 cm 2 V −1 s −1 ). The performance of the accumulation-mode TFTs fabricated under 400 °C also strongly depended on $\boldsymbol {x}_{\mathrm {i}}$ , achieving both a high field-effect mobility (170 cm 2 V −1 s −1 ) and on/off ratio (10 3 ) at ${x}_{\mathrm {i}} = 1.6$ %. This performance was shown to be the highest among Ge-based TFTs with grain boundaries in the channel.

In this article, the electrical properties of nMOSFET devices with different high-k Al₂O₃ capping layer thickness and TiN electrode have been systematically studied at deep cryogenic temperatures ranging from 10 to 300 K. The threshold voltage $V_{TH}$ , transconductance $g_{m}$ , carrier mobility μ, mobility attenuation factor θ , and subthreshold swing (SS) are extracted using the $I_{DS}$ - $V_{GS}$ curves and Y-function method at different temperatures. It is indicated that: 1) all the electrical parameters ( $V_{TH}$ , $g_{m}$ , μ, θ , and SS) show strong temperature dependence in the range of studied temperatures and 2) temperature-dependent electrical properties of nMOSFET devices will modulate at various cryogenic temperatures ascribed to the presence of the Al₂O₃ capping layer on the SiO₂ dielectric layer, which increases the oxide trap density and consequentially adjusts the threshold voltage and mobility of the devices.

The effects of the substituent in p-substituent-benzylidenemalononitrile small molecules have been investigated. We found that the replacement of cyano group in the molecule (M1) by a nitro group (M2) reduces the optical and the electrochemical band gap value which is correlated with a red shift in the absorption and photoluminescence spectra. The insertion of both molecules in P3HT and PCDTBT polymers showed that the quenching parameter efficiency increase from 42 to 71% and from 51 to 64%, respectively. We conclude that M2 is an efficient quencher in P3HT. Electrical measurements in dark showed a diode behaviour for all devices. The effective hole mobility μeff was calculated and shows an enhancement in the case of ITO/P3HT:M2/Al. The calculated values are comparable to those in the literature.

Large elongated single crystals (2.91 mm × 97 μm) of 1,6-dibromopyrene were successfully obtained from solution using the slow evaporation method. Their carrier mobility was obtained via current–voltage characteristics of bottom-gate bottom-contact-type field-effect transistors. In these devices, the longitudinal direction of each crystal was parallel or perpendicular to the conductive channel. The highest mobility was 6.0 × 10−4 cm2 V−1 s−1 and 2.2 × 10−3 cm2 V−1 s−1 in the linear and saturation region, respectively, when the electric current flowed across the crystal’s longitudinal direction. The emission strength ratio and mobility ratio between the two longitudinal directions (parallel and perpendicular to the conductive channel, respectively) were 3.1 and 2.2. X-ray diffraction measurements suggested that both the emission strength and mobility are larger in the transverse intermolecular contact direction than in the stacking direction. The mobilities in the linear region were tentatively corrected by subtracting the contributions of charge injection barriers and were estimated to be 2.1–2.9 times larger than the uncorrected ones. The results of this study suggest that bromine substitution is one of the effective methods to modify the optical properties and improve the solution processability of organic semiconductor materials while maintaining the carrier mobility.

Polycrystalline BiCuSeO is considered as a promising thermoelectric material due to its intrinsically low thermal conductivity and moderate Seebeck coefficient. However, its low electrical conductivity and coupled electron-phonon transport properties restrict the further improvement of the thermoelectric performance. In this work, Pb and Yb dopants are incorporated into BiCuSeO to substitute for Bi sites via ball milling and high-pressure and high-temperature sintering, leading to a synergistic optimization of the electron and phonon transport and improved thermoelectric performance. The carrier concentration exhibits an enhancement with increasing Pb&Yb co-doping contents. Meanwhile, the decreased carrier mobility is suppressed appropriately by coordinating with the interplay of Pb and Yb dopants on the electronic structure. Besides, Pb&Yb co-doping combined with high-pressure and high-temperature sintering introduces abundant grain boundaries, dislocations, and point defects to effectively decrease the lattice thermal conductivity by scattering phonons in a broad frequency range. Coupled with the synergistic optimization of the electrical and thermal properties, a maximum zT of 1.2 is achieved in Bi0.88Pb0.06Yb0.06CuSeO at 850 K, which significantly outperforms the majority of oxygen-containing thermoelectric materials. Our study suggests that dual doping of bivalent ions and rare-earth elements at Bi sites is an effective strategy for improving the thermoelectric performance of BiCuSeO.

Glasses with nominal composition 70Bi2O3–30Fe2O3 and 10X–60Bi2O3–30Fe2O3 (mol%); (X = Ba, Sr and Ca) were prepared by the conventional melt quenching technique. X-ray diffraction and differential scanning calorimeter confirm the amorphous nature of the glass samples. The iron-bismuth glass shows good solubility of alkaline earth elements ions. In temperatures range of 310–450 K, the dc conductivity of the glass samples containing alkaline earth elements enhanced. Glass sample containing Sr shows interesting electrical properties. All glass samples showed a transition from negative to positive Seebeck coefficient, this means that the conduction is mixed of electrons and holes charge carriers. The conduction mechanism of all samples obeys non-adiabatic small polaron hopping model of electron between iron ions. The calculated small polaron coupling constant, (γp) was found to be in the range of 10.25–17.28. Also, the calculated hopping mobility (μ) and carrier density (Nc) of glasses were in the range of 4.65 $$\times {10}^{- 7}$$ to 4.11 $$\times {10}^{-3},\left({\mathrm{cm}}^{2}\,{\mathrm{V}}^{-1}\,{\mathrm{s}}^{-1}\right)$$ and 0.029–10 $$({\times {10}^{17}\,\mathrm{cm}}^{-3})$$ at 333 K, respectively. The conductivity of the present glasses was primarily determined by hopping carrier mobility.

Achieving high electrical conductivity and thermoelectric power factor simultaneously for n-type organic thermoelectrics is still challenging. By constructing two new acceptor-acceptor n-type conjugated polymers with different backbones and introducing the 3,4,5-trimethoxyphenyl group to form the new n-type dopant 1,3-dimethyl-2-(3,4,5-trimethoxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (TP-DMBI) , high electrical conductivity of 11 S cm -1 and power factor of 32 μW m -1 K -2 are achieved. Calculations using Density Functional Theory show that TP-DMBI presents a higher singly occupied molecular orbital (SOMO) energy level of -1.94 eV than that of the common dopant 4-(1, 3-dimethyl-2, 3-dihydro-1H-benzoimidazol-2-yl) phenyl) dimethylamine (N-DMBI) (-2.36 eV), which can result in a larger offset between the SOMO of dopant and lowest unoccupied molecular orbital (LUMO) of n-type polymers, though that effect may not be dominant in the present work. The doped polymer films exhibit higher Seebeck coefficient and power factor than films using N-DMBI at the same doping levels or similar electrical conductivity levels. Moreover, TP-DMBI doped polymer films offer much higher electron mobility of up to 0.53 cm 2 V -1 s -1 than films with N-DMBI doping, demonstrating the potential of TP-DMBI, and 3,4,5-trialkoxy DMBIs more broadly, for high performance n-type organic thermoelectrics.

The copper phthalocyanine/single-walled carbon nanotube (CuPcI/SWCNT) hybrids were fabricated through doping the CuPc/SWCNT mixture using iodine vapor. It was found that both CuPc and SWCNTs were oxidized by iodine vapor resulting in great increase in carrier concentration. Moreover, the strong π-π conjugation interactions between CuPcI- and I-doped SWCNTs make the CuPcI molecules to assemble on the surface of SWCNTs in an ordered face-on packing, which benefits decreasing the carrier transport barrier across the CuPcI/SWCNT interfaces. The combination of iodine bidoping and the ordered face-on packing of CuPcI on the SWCNT surface realizes the synergetic enhancement of carrier concentration and carrier mobility and therefore the great improvement of electrical conductivity. The maximum electrical conductivity (6281 S cm-1) and thermoelectric power factor (∼304 μW m-1 K-2) at room temperature were obtained at a composition of 60 wt % SWCNTs. The power factor value is 3 orders of magnitude higher than the pure CuPcI and 1 order of magnitude higher than SWCNTs. Consequently, the highest ZT value of CuPc/SWCNT hybrids is up to 0.03, which is among the highest value of organic small-molecule complexes.

In this work, we predict two novel two-dimensional (2D) auxetic materials, BiSbX3 (X = S, Se) monolayers, through first-principles calculations. Attributed to their special braceletlike structure, the in-plane negative Poisson's ratio (NPR) of BiSbS3 and BiSbSe3 monolayers are as high as -0.25 and -0.26, respectively. The phonon dispersion calculations, ab initio molecular dynamics simulations, and elastic constants calculations demonstrate that these two monolayers possess excellent dynamic, thermal, and mechanical stabilities. The band gap values of BiSbS3 and BiSbSe3 calculated at the HSE level by considering the spin-orbit coupling (SOC) effect are 1.68 and 1.20 eV. The anisotropic carrier mobility and superior optical absorption indicate that they may shine in the next generation of electronic and optoelectronic devices. All of these discoveries not only enrich the types of auxetic materials but also provide a structural reference for designing new auxetic materials on the molecular level. Furthermore, they can provide theoretical guidance for future applications of BiSbX3 (X = S, Se) monolayers in various fields.

Strong intermolecular interactions in 2D organic molecular crystals arising from π-π stacking have been widely explored to achieve high thermal stability, high carrier mobility, and novel physical properties, which have already produced phenomenal progress. However, strong intermolecular interactions in 2D inorganic molecular crystals (2DIMCs) have rarely been investigated, severely limiting both the fundamental research in molecular physics and the potential applications of 2DIMCs for optoelectronics. Here, the effect of strong intermolecular interactions induced by unique short intermolecular Se-Se and P-Se contacts in 2D α-P4Se3 nanoflakes is reported. On the basis of theoretical calculations of the charge density distribution and an analysis of the thermal expansion and plastic-crystal transition, the physical picture of strong intermolecular interactions can be elucidated as a higher charge density between adjacent P4Se3 molecules, arising from an orderly and close packing of P4Se3 molecules. More importantly, encouraged by the strong intermolecular coupling, the in-plane mobility of α-P4Se3 nanoflakes is first calculated with a quantum nuclear tunneling model, and a competitive hole mobility of 0.4 cm2 V-1 s-1 is obtained. Our work sheds new light on the intermolecular interactions in 2D inorganic molecular crystals and is highly significant for promoting the development of molecular physics and optoelectronics.