High Hole Mobility Research Articles

In Situ Defect Engineering of Controllable Carrier Types in WSe2 for Homomaterial Inverters and Self-Powered Photodetectors.

WSe2 has a high mobility of electrons and holes, which is an ideal choice as active channels of electronics in extensive fields. However, carrier-type tunability of WSe2 still has enormous challenges, which are essential to overcome for practical applications. In this work, the direct growth of n-doped few-layer WSe2 is realized via in situ defect engineering. The n-doping of WSe2 is attributed to Se vacancies induced by the H2 flow purged in the cooling process. The electrical measurements based on field effect transistors demonstrate that the carrier type of WSe2 synthesized is successfully transferred from the conventional p-type to the rarely reported n-type. The electron carrier concentration is efficiently modulated by the concentration of H2 during the cooling process. Furthermore, homomaterial inverters and self-powered photodetectors are fabricated based on the doping-type-tunable WSe2. This work reveals a significant way to realize the controllable carrier type of two-dimensional (2D) materials, exhibiting great potential in future 2D electronics engineering.

Predicting and analyzing the fill factor of non-fullerene organic solar cells based on material properties and interpretable machine-learning strategies

In recent years, encouraging progress in non-fullerene acceptors-based organic solar cells (NFAs-OSCs) has been made in the field of clean-energy technologies. Nevertheless, achieving a high fill factor (FF) for NFAs-OSCs is a great challenge due to the FF value can be dramatically affected by various factors. An accurate prediction (based on empirical data) of how inherent characteristics of polymer-NFA combinations (e.g., frontier molecular orbitals (FMO) and charge-carrier mobilities) affects the FF in NFAs-OSCs is therefore urgently needed for the future commercialization prospect. The presented work demonstrates an outperforming predictive model using the optimized Gradient-boosting decision tree (GBDT) machine learning (ML) algorithm to accurately predict the FF value, which is based on a dataset consisting of > 180 unique donor/NFA blends with reported FF from previously published publications and experimental physical descriptors (FMO and charge-carrier mobilities). In addition, the SHapley Additive exPlanations (SHAP) strategy is further applied to not only gain the interpretability of the GBDT model prediction but also directly map the relationship between the FF value and experimental physical descriptors by systematic interpretable explanations (e.g., global and local). The SHAP analysis qualitatively reveals that the highest occupied molecular orbital (HOMO) of the donor and the HOMO of the acceptor are the two most important features associated with FF value prediction, which is in good agreement with previous experimental facts. Furthermore, the ML strategies explore the key requirements (e.g., small HOMO offset (<0.3 eV), high hole and electron mobilities (>1.0 × 10–4 cm2 V−1 s−1), and desired μh/μe ratio (in the range of 1.8–3.3)) for enhancing the FF values of NFAs-OSCs. This study provides novel insights into the possible physical mechanisms of FF enhancement, thus facilitating research efforts (e.g., rational design of energy level tuning in donor/NFA blend) for high-performance NFAs-OSCs.

Electronic properties by polarization-inducing of the F-GaN-H/SiC van der Waals hetero-structures

Atomic doping plays an important role in the fabrication of electronic devices. However, the atomic doping of two-dimensional materials is challenging as the thickness approaches the nanoscale. Self-doping, achieved through an asymmetric structure, can simplify the fabrication of electronic devices. In this study, the electronic properties of the F-GaN-H/SiC hetero-structures are investigated based on the first principles. The intrinsic polarization of the F-GaN-H leads to charge transfer resulting in self-doping. The spatial distribution of carriers in the F-GaN-H/SiC hetero-structures is reversed with polarization reversal. And p-type doped F-GaN-H and n-type doped SiC are achieved in polarization-down (Pd) hetero-structures, which is contrary to polarization-up (Pu) hetero-structures. The band gaps of the F-GaN-H/SiC hetero-structures are smaller than the intrinsic materials, and the band structures are modulated by polarization direction. For the Pu hetero-structures, a high hole mobility of 8.87 × 103 cm2 V−1 s−1 is achieved. The self-doping and the excellent transport properties of the F-GaN-H/SiC hetero-structures, with the tunable bandgap structures to polarization direction, not only simplify the fabrication of electronic devices but also demonstrate the potential application for optoelectronic and high-speed electronic devices.

Substitution Position Effects on Spiro[Fluorene‐9,9′‐Xanthene]‐Diphenylamine Hole‐Transporting Materials for Perovskite Solar Cells

The molecular structures of hole‐transporting materials (HTMs) have a significant effect on the performance of perovskite solar cells (PSCs). In this work, four small‐molecular HTMs (SFX‐1, SFX‐2, SFX‐3, and SFX‐4) are prepared by regulating the substitution sites of terminal diphenylamine groups on the spiro[fluorene‐9,9′‐xanthene] core. As SFX‐1 and SFX‐2 are well‐documented compounds, this article adopts the original publication's acronyms, referring to them as SFX‐MeOTAD and HTM‐FX′, respectively. It is found that the terminal substitution sites exhibit a noticeable effect on the molecular properties. Among these molecules, SFX‐3, whose terminal groups are located at the 3,6‐substitution site on the fluorene side of SFX, has high conductivity and hole mobility, and the highest occupied molecular orbital level matches well with the perovskite. SFX‐3 also shows better film‐forming properties and better hole extraction ability than the molecules with other substitution sites. Higher power conversion efficiency (PCE) in PSCs with SFX‐3 is comparable to that of traditional spiro‐OMeTAD, but SFX‐3's synthesis cost is only about one‐third that of spiro‐OMeTAD. Furthermore, the device utilizing SFX‐3 exhibits remarkable stability, surpassing that of spiro‐OMeTAD. Notably, the champion PCE of SFX‐3‐based PSCs reached 22.42%, marking the highest reported efficiencies among HTMs with SFX as the core.

Decoupling the Trade‐Off Between the Photosignal and Photonoise in Upconversion Devices Through a Solution‐Processed Nickel Oxide Interconnecting Layer

AbstractNear‐infrared (NIR) to visible upconversion devices (UCDs) provide a viable and cost‐effective way for NIR visualization and pixel‐less imaging techniques. An excellent electrical connection between the NIR detection unit and the visible emission unit in the UCD is one of the prerequisites for achieving efficient upconversion performance. In this study, a low temperature‐ and solution‐processed nickel oxide (NiOx) interconnecting layer (ICL) with high hole mobility and favorable energy levels is demonstrated to decouple the trade‐off between photosignal and photonoise in the UCDs. The use of such a NiOx ICL suppresses intrinsic visible emission in the dark (photonoise) but enhances visible light output under NIR illumination (photosignal) by triggering an efficient charge injection in the UCDs. As a result, a hybrid UCD monolithically integrating an organic NIR photodetector and a visible quantum dot light‐emitting diode via the NiOx ICL achieves excellent performance, exhibiting an ultralow turn‐on voltage as low as 1.6 V, a high luminance close to 6.3 × 103 cd m−2, a wide operation voltage window up to 7.4 V, and a high contrast ratio reaching 5 × 104. The resulting UCD is also used for imaging demonstrations showing clear visible images of the NIR targets, which paves the way for practical applications.

Approaching Theoretical Limits in the Performance of Printed P-Type CuI Transistors via Room Temperature Vacancy Engineering.

Development of a novel high performing inorganic p-type thin film transistor could pave the way for new transparent electronic devices. This complements the widely commercialized n-type counterparts, indium-gallium-zinc-oxide (IGZO). Of the few potential candidates, copper monoiodide (CuI) stands out. It boasts visible light transparency and high intrinsic hole mobility (>40 cm2 V-1 s-1 ), and is suitable for various low-temperature processes. However, the performance of reported CuI transistors is still below expected mobility, mainly due to the uncontrolled excess charge- and defect-scattering from thermodynamically favored formation of copper and iodine vacancies. Here, a solution-processed CuI transistor with a significantly improved mobility is reported. This enhancement is achieved through a room-temperature vacancy-engineering processing strategy on high-k dielectrics, sodium-embedded alumina. A thorough set of chemical, structural, optical, and electrical analyses elucidates the processing-dependent vacancy-modulation and its corresponding transport mechanism in CuI. This encompasses defect- and phonon-scattering, as well as the delocalization of charges in crystalline domains. As a result, the optimized CuI thin film transistors exhibit exceptionally high hole mobility of 21.6 ± 4.5 cm2 V-1 s-1 . Further, the successful operation of IGZO-CuI complementary logic gates confirms the applicability of the device.

S-scheme SnO/TiO2 heterojunction with high hole mobility for boosting photocatalytic degradation of gaseous benzene

Enhancing the efficiency of carrier migration and separation plays a pivotal role in promoting photocatalytic performance. Constructing S-scheme heterojunction is a promising strategy to achieve this desired objective. Here, we rationally designed and preciously synthesized SnO{001}/TiO2{001} S-scheme heterojunction with exceptionally high hole mobility (1122 cm2/(V·s)), which ranks among the best of reported works. SnO{001}/TiO2{001} heterojunctions exhibited outstanding performance of gaseous benzene degrading. The degradation rate constant of SnO/TiO2 heterojunction is 2.4675 h−1, and is boosted by 5.3 times compared with TiO2 (0.4595 h−1). Through the combination of theoretical calculation and experiment, S-scheme mode of carrier transferring was verified. The promoted hole mobility in SnO/TiO2 heterojunction enhances the production of ·OH, further boosting photocatalytic performance. By analyzing the detected intermediates, we proposed degradation pathways for benzene, which provide a profound and elucidating view of complex processes in benzene photocatalytic degradation.

Fully-Locked conjugated core substitution improves the π-π stacking and mobility of hole-transporting materials for perovskite solar cells

A new hole-transporting materials (HTMs) TTE-3 was designed by introducing a fully-locked conjugated naphthalene group into the 2,2′7,7′- tetrakis (N, N-p-dimethoxy-phenylamino)-9,9′- tetrathienylethene (TTE-2). Density functional theory, Marcus theory and Einstein relation were used to investigate the influence of fully-locked conjugated core on geometric structure, electronic properties and transport properties. Results show that the small reorganization energy is achieved owing to the small steric hindrance of TTE-3. And the more effective π-π stacking and larger orbital overlap between HOMOs of dimers promote larger intermolecular electronic coupling. TTE-3 has a higher hole mobility (4.52 cm2V-1s−1) than TTE-2 (1.00 × 10-1 cm2V-1s−1). In addition, calculated hydrophobicity of TTE-3 is greater than that of TTE-2, which can evaluate a longer service life of PSCs applying TTE-3 as HTMs. The design and theoretical simulation of TTE-3 provides a useful selection route for the high-performance small molecular HTMs.

High-Efficiency and Low-Energy-Loss Organic Solar Cells Enabled by Tuning the End Group Modification of the Terthiophene-Based Acceptor Molecules to Enhance Photovoltaic Properties.

In the current study, six nonfullerene small acceptor molecules were designed by end-group modification of terminal acceptors. Density functional theory calculations of all designed molecules were performed, and optoelectronic properties were computed by employing different functionals. Every constructed molecule has a significant bathochromic shift in the maximum absorption value (λmax) except AM6. AM1-AM4 molecules represented a narrow band gap (Eg) and low excitation energy values. The AM1-AM4 and AM6 molecules have higher electron mobility. Comparing AM2 to the reference molecule reveals that AM2 has higher hole mobilities. Compared to the reference molecule, all compounds have excellent light harvesting efficiency values compared to AM1 and AM2. The natural transition orbital investigation showed that AM5 and AM6 had significant electronic transitions. The open-circuit voltage (Voc) values of the computed molecules were calculated by combining the designed acceptor molecules with PTB7-Th. In light of the findings, it is concluded that the designed molecules can be further developed for organic solar cells (OSCs) with superior photovoltaic abilities.

Strategy for enhancing the Tg of linear hole-transporting materials without sacrificing solubility toward efficient and stable perovskite solar cells

Linear small hole transport materials (HTMs) with strong π−π interactions show high hole mobility. However, they suffer from inferior glass transition temperature (Tg) and low solubility, which adversely affect surface morphology of HTMs, compromising the stability of perovskite solar cells (PSCs). In this work, we describe a new molecular design strategy to enhance the Tg of linear small HTMs without sacrificing the solubility, that is, constructing HTMs with fluorinated planar donor and π-bridge containing noncovalent conformational locking. The resulting linear HTM SL22 represents a high Tg and crystallization temperature while having a good solubility, leading to optimal film morphology. Moreover, SL22-based devices show improved hole-transporting properties, thermal stability and reduced non-radiative recombination as compared to the control device based on SL21. As a result, the optimized PSCs based on doped and dopant-free SL22 deliver a high PCE of 22.26 % and 19.53 %, respectively. Importantly, the unencapsulated device based on SL22 maintains over 94 % of its initial efficiency after 800 h at 60 °C in the N2 filled glove-box.

AlSb/ZrS2 heterojunction: A direct Z-scheme photocatalyst with high solar to hydrogen conversion efficiency and catalytic activity across entire PH range

Using the First principles method, the electrical, optical, and photocatalytic characteristics of AlSb/ZrS2 van der Waals heterojunctions (vdwH) with direct Z-scheme photogenerated electron transfer mechanism were calculated in this study. The inherent type-II band structure, the built-in electric field that facilitates photogenerated carrier separation, and the high mobility of electrons and holes along the x and y axes all contribute to the strong photocatalytic activity. Furthermore, the AlSb/ZrS2 van der Waals heterojunction has better light absorption performance than monolayers, with a light absorption coefficient of 4.7 × 105 cm−1 at 500 nm and a solar to hydrogen efficiency of 25.81%. Meanwhile, the breakdown reaction of heterojunctions for water can be spontaneously reacted under the light, according to the free energy calculations of the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) processes. Unexpectedly, adding biaxial strain to the heterojunction allows for effective band gap and light absorption coefficient adjustments. and the photolysis reaction of water can be realized in the whole PH range within a suitable strain range. The AlSb/ZrS2 van der Waals heterojunction is expected to be a promising candidate for Z-scheme heterojunction photocatalysts for the whole hydrolysis in the future.

Porphyrin-Anhydride Co-Sensitization Strategy for Enhanced Photovoltaic Performance in DSSC: A Combined Experimental and Theoretical Approach

A new covalently linked porphyrin-based anhydride(C108H86N10O4Zn2) named TPP-PMDI-TPP has been successfully synthesized through a simple thermal imidization reaction of electron-donating Zn(5-(4-aminopheny)-10,15,20-triphenylporphyrin(Zn-ATPP) and electron-accepting pyromellitic dianhydride(PMDA) moieties and tested in the of photovoltaic application. TPP-PMDI-TPP was subjected to comprehensive characterization using various analytical techniques, including FT-IR, 1H NMR, UV–visible, PXRD, cyclic voltammetry, and molecular simulation. Fluorescence studies were also employed to characterize TPP-PMDI-TPP. Excellent fluorescence quenching of 95 % was observed in TPP-PMDI-TPP, indicating remarkable electron transfer from porphyrin to pyromellitic dianhydride within TPP-PMDI-TPP. The cyclic voltammetric analysis provided the HOMO and LUMO values of TPP-PMDI-TPP as −6.172 eV and −4.185 eV, respectively. The investigation of the charge-transfer phenomenon in the entitled compound was assessed using FMOs. Results obtained from cyclic voltammetry and computational calculations for HOMO, LUMO, and band gap (Eg) of porphyrin-based anhydride (TPP-PMDI-TPP) are in well concordance, indicating the practicality of the utilized experimental approach. Global reactivity parameters were obtained by using HOMO–LUMO energies of compounds. The photovoltaic measurements of ITO-coated TPP-PMDI-TPP film was performed to check different photovoltaic parameters (VOC, ISC, FF, and η), showing values of about 0.858 V, 8.1794 mA/cm2, 0.561 and 3.9 % respectively, calculated from current-voltage (I–V) graph. The lower photocurrent and power conversion efficiency in the TPP-PMDI-TPP film is due to the electron withdrawal caused by the dianhydride group, transferring electrons from porphyrin to PMDA. This electron-withdrawing effect leads to imbalanced charge transport, with higher hole mobilities than electron mobilities, resulting in lower efficiency for TPP-PMDI-TPP-based photovoltaic cells.

An Unsymmetrical 5,15-Disubstituted Tetrabenzoporphyrin: Effect of Molecular Symmetry on the Packing Structure and Charge Transporting Property.

Molecular design strategy to control the crystal structure of two-dimensional (2D) π-extended organic semiconductors has not been intensively explored. We synthesized an unsymmetric tetrabenzoporphyrin derivative (TIPS-Ph-BP) to demonstrate the effect of molecular symmetry on crystal packing. TIPS-Ph-BP formed an antiparallel slipped π-stacking and 2D herringbone-like structure. An unsymmetric structure would make 2D π-stacking more stable than a one-dimensional (1D) columnar structure to counteract steric and electronic imbalance in the crystal. As a result, TIPS-Ph-BP achieved the high hole mobility of 0.71 cm2 V-1 s-1.

Back interface management by multifunctional composite carbon nanospheres electrode for efficient and stable HTL-free carbon-based perovskite solar cells

The fabrication of a carbon electrode with high hole extraction and simultaneous the function of improving back interface properties is a critical and efficient strategy to enhance the performance of carbon-based perovskite solar cells (C–PSCs) free of hole transport layer (HTL). Herein, a compound of MoS2 and MoP in situ composite N, P co-doped carbon nanospheres (MoS2–MoP/NPC) is constructed as an efficient carbon electrode for HTL-free PSCs. The excellent p-type characteristic of MoS2, the high conductivity of MoP and the co-doping of N, P heteroatoms endow the composite carbon nanospheres with high hole mobility and conductivity and a down-shifted work function, which significantly promotes the extraction and transportation of holes and decreases energy loss. Meanwhile, the N, P and S components of the MoS2–MoP/NPC nanospheres exert a passivation effect on the surface free positive ions defects of the perovskite film, resulting in a remarkable reduction in non-radiative recombination at back interface. As a result, the HTL-free CsPbBr3 PSCs without any encapsulation based on MoS2–MoP/NPC electrode achieve a champion power conversion efficiency of 10.13% with a significant open-circuit voltage of 1.638 V and excellent long-term stability after storage at 85% RH, 85 °C in air for 30 days. This work provides a new perspective for designing multifunctional carbon electrode materials that holistically optimize the back interface to improve the efficiency and stability of HTL-free C–PSCs.

Chalcogenopheno[3,2-b]pyrrole-Containing Donor-Acceptor-Donor Organic Semiconducting Small Molecules for Organic Field-Effect Transistors.

A group of chalcogenopheno[3,2-b]pyrroles, including thieno[3,2-b]pyrrole (TP), furo[3,2-b]pyrrole (FP), and selenopheno[3,2-b]pyrrole (SeP), and thieno[3,2-b]thiophene (TT) electron-donating units were coupled with a thiophene-flanked diketopyrrolo[3,4-c]pyrrole (ThDPP) acceptor to generate four donor-acceptor-donor (D-A-D) semiconducting small molecules (ThDPP-TT, ThDPP-FP, ThDPP-TP, and ThDPP-SeP). This study systematically investigated the differences between chalcogenopheno[3,2-b]pyrroles and TT. From the characterizations, chalcogenopheno[3,2-b]pyrrole-containing molecules showed lower band gaps and binding-energy cold crystallization behavior. The enthalpies of cold crystallization were correlated with the weight of the chalcogen in ThDPP-FP, ThDPP-TP, and ThDPP-SeP, which were evaluated as intermolecular chalcogen-bond interactions between chalcogen and pyrrole nitrogen in chalcogenopheno[3,2-b]pyrroles. A stronger chalcogen bond interaction resulted in stronger self-aggregation in thin films with thermal treatment, which resulted in a polycrystalline structure in chalcogenopheno[3,2-b]pyrrole-containing molecules. For the application in an organic field-effect transistor, all four molecules showed good performance with the highest hole mobilities as 6.33 × 10-3 cm2 V-1 s-1 for ThDPP-TT, 2.08 × 10-2 cm2 V-1 s-1 for ThDPP-FP, 1.87 × 10-2 cm2 V-1 s-1 for ThDPP-TP, and 6.32 × 10-3 cm2 V-1 s-1 for ThDPP-SeP, and the change of mobility is well correlated to the root-mean-square roughness of the thin films. Overall, all the chalcogenopheno[3,2-b]pyrrole-containing molecules showed lower band gaps, polymorphism, and better charge transport properties compared to TT-containing molecules, which motivates replacing TT with chalcogenopheno[3,2-b]pyrroles in conjugated polymers, non-fullerene small molecular acceptors, and narrow-band-gap donors.

Two-Dimensional Silver-Chalcogenolate-Based Cluster-Assembled Material: A p-type Semiconductor.

We have synthesized and characterized a new two-dimensional honeycomb architecture resembling a single-layer of atomically precise silver cluster-assembled material (CAM), [Ag12(StBu)6(CF3COO)6(4,4'-azopyridine)3] (Ag12-azo-bpy). The interlayer noncovalent van der Waals interactions within the single-crystals were successfully disrupted, leading to the creation of this unique structure. The optimized Ag12-azo-bpy CAM demonstrates a valence band that is localized on the Ag12 cluster node situated near the Fermi energy level. This localization induces electron injection from the linker to the cluster node, facilitating efficient charge transportation along the plane. Exploiting this single-layer structure as a distinctive platform for p-type channel material, it was employed in a field-effect transistor configuration. Remarkably, the transistor exhibits a high hole mobility of 1.215 cm2 V-1 s-1 and an impressive ON/OFF current ratio of ∼4500 at room-temperature.

Low-Temperature Cross-Linkable Hole Transport Materials for Solution-Processed Quantum Dot and Organic Light-Emitting Diodes with High Efficiency and Color Purity.

Cross-linkable hole transport materials (HTMs) are ideal for improving the performance of solution-processed quantum dot light-emitting diodes (QLEDs) and phosphorescent light-emitting diodes (OLEDs). However, previously developed cross-linkable HTMs possessed poor hole transport properties, high cross-linking temperatures, and long curing times. To achieve efficient cross-linkable HTMs with high mobility, low cross-linking temperature, and short curing time, we designed and synthesized a series of low-temperature cross-linkable HTMs comprising dibenzofuran (DBF) and 4-divinyltriphenylamine (TPA) segments for highly efficient solution-processed QLEDs and OLEDs. The introduction of divinyl-functionalized TPA in various positions of the DBF core remarkably affected their chemical, physical, and electrochemical properties. In particular, cross-linked 4-(dibenzo[b,d]furan-3-yl)-N,N-bis(4-vinylphenyl)aniline (3-CDTPA) exhibited a deep highest occupied molecular orbital energy level (5.50 eV), high hole mobility (2.44 × 10-4 cm2 V-1 s-1), low cross-linking temperature (150 °C), and short curing time (30 min). Furthermore, a green QLED with 3-CDTPA as the hole transport layer (HTL) exhibited a notable maximum external quantum efficiency (EQEmax) of 18.59% with a remarkable maximum current efficiency (CEmax) of 78.48 cd A-1. In addition, solution-processed green OLEDs with 3-CDTPA showed excellent device performance with an EQEmax of 15.61%, a CEmax of 52.51 cd A-1, and outstanding CIE(x, y) color coordinates of (0.29, 0.61). This is one of the highest reported EQEs and CEs with high color purity for green solution-processed QLEDs and OLEDs using a divinyl-functionalized cross-linked HTM as the HTL. We believe that this study provides a new strategy for designing and synthesizing practical cross-linakable HTMs with enhanced performance for highly efficient solution-processed QLEDs and OLEDs.

Two birds with one stone: dopant-free squaraine hole-transporting material for perovskite solar cell

Developing alternative dopant-free hole-transporting materials (HTM) with a passivation effect and high hole mobility is significant for enhancing the power conversion efficiency (PCE) and stability of the perovskite solar cells (PSCs) with a simplified process. In this work, we report a squaraine HTM 3,4-bis(4'-(bis(4-methoxyphenyl)amino)-[1,1′-biphenyl]-4-yl)cyclobut-3-ene-1,2-dione (D12) with a resonance central structure shuttling between electrically neutral dione and charge-separated inner salts. The donor-acceptor-donor type molecule D12 exhibits an extremely strong capacity not only for hole exaction and mobility, but also for the passivation of perovskite defects. This results in a high PCE of 22.32% for D12-based PSCs. After 30 days of aging at a high relative humidity of 65% at 30 °C, it remains 90% of its initial PCE. This work offers a strategy of designing dopant-free small-molecule HTM and enhancing the stability and PCE of PSCs.

Reversal of Band-Ordering Leads to High Hole Mobility in Strained p-type Scandium Nitride.

Low hole mobility of nitride semiconductors is a significant impediment to realizing their high-efficiency device applications. Scandium nitride (ScN), an emerging rocksalt indirect band gap semiconductor, suffers from low hole mobility. Utilizing the ab initio Boltzmann transport formalism including spin-orbit coupling, here we show the dominating role of ionized impurity scattering in reducing the hole mobility in ScN thin films. We suggest a route to increase the hole mobility by reversing band ordering through strain engineering. Our calculation shows that the biaxial tensile strain in ScN lifts the split-off hole band above the heavy hole and light hole bands, leading to a lower hole-effective mass and increasing mobility. Along with the impurity scattering, the Fröhlich interaction also plays a vital role in the carrier scattering mechanism due to the polar nature of ScN. Increased hole mobility in ScN will lead to higher efficiencies in thermoelectric, plasmonics, and neuromorphic computing devices.

Computational Approach for Molecular Design of Small Organic Molecules with High Hole Mobilities in Amorphous Phase Using Random Forest Technique and Computer Simulation Method

Abstract A molecular design system of small organic molecules was developed to realize high hole mobility in the amorphous phase by using the random forest (RF) technique and a computer simulation method. Since there was no accessible datasets of the hole mobilities in the amorphous phase, we have constructed a datasets of experimental hole mobilities for 321 organic molecules with calculated MO energies to utilize machine learning techniques for molecular design procedures. RF was applied to the machine learning technique using the constructed datasets. The optimized RF exhibited correlation coefficients of 0.885 and 0.764 for the training and testing datasets, respectively. The modified ChemTS to use optimized RF was adapted to design molecules with high hole mobilities. The successive conduction (SC) model that uses ab initio molecular orbital (MO) calculations and the Marcus theory was adapted to ensure the predicted mobilities. The generated molecules were verified to have high calculated hole mobility (the order of 10−2 cm2/Vs) owing to the highest transfer integral and lowest reorganization energy by the theoretical successive conduction (SC) model. The datasets and programs used in this work were publicly released on GitHub.