Hole Mobility Enhancement Research Articles

High-performance p-type transparent conducting CuI–Cu2O thin films with enhanced hole mobility, surface, and stability

We employed reactive magnetron sputtering and iodination process at room temperature to deposit CuI–Cu2O films with enhanced hole mobility, surface, and stability.

Dopant-Free Bithiophene-Imide-Based Polymeric Hole-Transporting Materials for Efficient and Stable Perovskite Solar Cells.

The development of hole-transport materials (HTMs) with high mobility, long-term stability, and comprehensive passivation is significant for simultaneously improving the efficiency and stability of perovskite solar cells (PVSCs). Herein, two donor-acceptor (D-A) conjugated polymers PBTI and PFBTI with alternating benzodithiophene (BDT) and bithiophene imide (BTI) units are successfully developed with desirable hole mobilities due to the good planarity and extended conjugation of molecular backbone. Both copolymers can be employed as HTMs with suitable energy levels and efficient defect passivation. Shortening the alkyl chain of the BTI unit and introducing fluorine atoms on the BDT moiety effectively enhances hole mobility and hydrophobicity of the HTMs, leading to improved efficiency and stability of PVSCs. As a result, the organic-inorganic hybrid PVSCs with PFBTI as the HTM deliver a power conversion efficiency (PCE) of 23.1% with enhanced long-term operational and ambient stability, which is one of the best efficiencies reported for PVSCs with dopant-free polymeric HTMs to date. Moreover, PFBTI can be applied in inorganic PVSCs and perovskite/organic tandem solar cells, achieving a high PCE of 17.4% and 22.2%, respectively. These results illustrate the great potential of PFBTI as an efficient and widely applicable HTM for cost-effective and stable PVSCs.

Evaluation of Strained Group IV Semiconductor Devices by Oil-Immersion Raman Spectroscopy

We investigated stress evaluation of strained group IV semiconductor devices by oil-immersion Raman spectroscopy. In the oil-immersion Raman spectroscopy the high-numerical-aperture lens gives evaluation of complicated stress states in strained group IV semiconductor devices. As an example of the stress evaluation, a clear stress relaxation of the extremely thin body germanium on insulator (ETB GOI) channels was observed. This behavior indicates that the uniaxial stress is applied into GOI channels by patterning narrow channel. We confirmed that the uniaxial stress is applied into GOI channels by narrow channel patterning at even in ETB GOI channels down to approximately 4 nm by oil-immersion Raman spectroscopy, and stress relaxion (quasi-uniaxial stress) in GOI channels and hole mobility enhancement have good correlation.

A comparative study on performance of junctionless Bulk SiGe and Si FinFET

In this paper, the n-type and p-type SiGe junctionless bulk FinFET (SiGe JL-FinFET) with a high Ge mole fraction (xF>0.8) was studied for characteristics of a single device and the CMOS logic circuit using 3D numerical simulation. A comparison study between SiGe JL-FinFET and Si JL-FinFET under 1×1019 to 5×1019 doping concentrations. The SiGe JL-FinFET exhibits a 28% and 9% enhancement of hole and electron mobility, thus the saturation current, transconductance, intrinsic gain, and intrinsic delay are improved up to 38%, 26%, 45% and 27% in the SiGe-based device as compared to the Si-based device. Due to the higher mobility and lower gate capacitance of SiGe JL-FinFET, the rise time, fall time, propagation delay, and maximum operating frequency of the CMOS inverter are also improved up to 34%, 13%, 9%, and 20%, respectively, compared to their Si-based counterparts. This SiGe junctionless device has a simple fabrication process and improvements in analog and digital performance at the sub-5 nm technology node, making this device a promising architecture for high-performance CMOS logic applications.

Preparation of Sb2S3 nanorod arrays by hydrothermal method as light absorbing layer for Sb2S3-based solar cells

• Wet methods of synthesizing antimony sulfide nanorod arrays are proposed. • Controllable density, length, and aspect ratio of nanorod arrays. • Hole mobility is far larger in nanorod arrays than bulk layer or randomly stacked nanorods. Antimony sulfide (Sb 2 S 3 ) as a stable and nontoxic semiconductor reveals great potential for photovoltaic devices. Sb 2 S 3 has a one-dimensional crystal structure consisting of covalently bonded (Sb 4 S 6 ) n ribbons stacking together through van der Waals force. This special structure results in anisotropic electrical and optical properties. Currently, most Sb 2 S 3 photovoltaic device studies have been focused on the grain orientation in the Sb 2 S 3 thin film absorbers. However due to the one-dimensional crystal structure, nanorods arrays is more favored for carrier directional transport between layers than bulk thin film. In this context, effective approaches to enhance the carrier mobility by applying Sb 2 S 3 nanorod arrays as light absorber are urgently required. Herein this study introduces a hydrothermal method prepared Sb 2 S 3 nanorod arrays that grown on certain substrates. Series of Sb 2 S 3 nanorod arrays with different length, diameter, nanorod density per area, and hole mobility were fabricated by using different precursors or ligand and controlling reaction time. An efficiency of 1.46% and a hole mobility of 30.9 cm 2 V –1 s –1 were attained with an optimized device structure of glass-fluorine-doped tin oxide/ZnO/ZnO–ZnS/Sb 2 S 3 nanorod arrays/poly(3-hexylthiophene-2,5-diyl)/MoO x /Ag, which were 5.1 times higher in efficiency and 2.5 times higher in hole mobility than those of the control group using non-oriented randomly stacked nanorods as light absorber. This research provides an approach to fabricate Sb 2 S 3 nanorod arrays and verifies the enhancement of hole mobility in Sb 2 S 3 nanorod arrays, which provides a perspective for efficient Sb 2 S 3 -based solar cells.

Lead-doped cubic tin sulfide thin films for solar cell applications

Cubic tin sulfide (SnS), an earth-abundant and non-toxic material, is a promising candidate for thin film solar cells. Lead(Pb)-doped (0.0–11.6 atomic percent (at.%)) cubic SnS thin films were prepared via chemical bath deposition to achieve improved structural, optical, and electrical properties. X-ray diffraction studies revealed that the films were polycrystalline and exhibited cubic crystal structure, decreased crystallite size, and increased lattice parameter, strain, and dislocation density on increasing Pb content. Field emission scanning electron microscopy images revealed increased grain size up to 2.5 at.% and decreased grain size beyond 2.5 at.% of Pb content. Optical absorption studies showed a decrease in the band gap from 1.73 to 1.64 eV upon increasing the Pb dopant concentration. Hall measurements revealed an increase in the hole mobility up to 2.5 at.% and decreased mobility beyond the 2.5 at.% of Pb dopant concentration. In conclusion, the prepared cubic SnS films have potential for application in solar cells because of the demonstrated reduced optical band gap and enhanced hole mobility resulting from Pb-doping.

Solid solution effect boosts the photovoltaic performance of PCDTBT-based organic solar cells

Cheap conjugated polymer PCDTBT and its derivatives are rarely used in high-efficiency non-fullerene acceptor (NFA) organic solar cells (OSCs) due to their poor charge transport property. Herein, solid solution strategy is employed to boost the photovoltaic performance of PCDTBT:NFA-based OSCs. The PCDTBT-OR:PC 71 BM solid solution is formed when a small amount of PC 71 BM molecules are dispersed within amorphous PCDTBT-OR matrix due to their thermodynamic miscibility, which demonstrates increased hole mobility with comparison to the neat PCDTBT-OR. The hole mobility of ternary PCDTBT-OR:PC 71 BM:Y6 blend containing a small amount of PC 71 BM is also increased significantly due to the PCDTBT-OR:PC 71 BM solid solution effect. The ternary PCDTBT-OR:PC 71 BM:Y6 blend shows better charge extraction, less bimolecular recombination as well as more efficient charge transfer. Finally, the PCDTBT-OR:PC 71 BM:Y6 OSCs achieve a power conversion efficiency (PCE) of 8.42%, much higher than 6.82% of the binary PCDTBT-OR:Y6 OSCs, and it is also one of the highest values for PCDTBT:NFA-based OSCs. This work demonstrates that the cheap polymer donor PCDTBT derivatives have potential to achieve high PCE in combination with NFAs. Solid solution effect of PCDTBT-OR:PC 71 BM blend is favorable to enhance hole mobility of donor phase and renders the PCDTBT-OR:Y6-based organic solar cells (OSCs) an optimized PCE of 8.42%, which is one of the highest values for the PCDTBT:NFAs based OSCs. • Solid solution effect is utilized to improve the photovoltaic performance of PCDTBT-OR:NFA OSCs. • PC 71 BM molecules tend to disperse in PCDTBT-OR matrix to form solid solutions. • Solid solution effect is favorable to improve hole transport in PCDTBT-OR:PC 71 BM blend film. • Solid solution effect enhances the hole mobility and suppresses bimolecular recombination in the ternary blend. • The optimized device achieves a PCE of 8.42%, which is one of the highest values for the PCDTBT:NFA based OSCs.

Enhanced Hole Mobility and Decreased Ion Migration Originated from Interface Engineering for High Quality PSCs with Average FF beyond 80.

Perovskite solar cells (PSCs) have made significant progress in power conversion efficiency (PCE) by optimizing deposition method, composition, interface, etc. Although the two-step method demonstrates the advantage of being easy to operate, too much residual PbI2 not only forms defect centers, but affects the perovskite crystallization by arising more grain boundaries (GBs) due to the easy-to-crystallize nature of PbI2 . And GBs in polycrystalline perovskite usually provide main channel for ion migration, leading to accumulation of charges at the interface to form a barrier, thus reducing carrier mobility and resulting in degradation of perovskite devices. Here, an organic molecule N-(4-acetylphenyl)maleimide (N-APMI) is used to modify interface between perovskite and hole transport layer. X-ray photoelectron spectroscopy, scanning electron microscope, and nuclear magnetic resonance results show that ketone group (CO) in N-APMI forms a strong coordination with Pb2+ , which effectively reduces the residual amount of PbI2 nanoparticles on the perovskite surface, giving rise to improved crystallization of perovskite. Temperature-dependent current response demonstrates that ion migration is effectively suppressed, and hole mobility validly increases from 10.74 to 19.48 cm2 V-1 s-1 , leading to a champion fill factor (FF) of 82.5% (PCE 21.96%), and the maximum PCE of the device improves from 20.09% to 23.03%.

Enhancing the photovoltaic properties of SnS-Based solar cells by crystallographic orientation engineering

Tin monosulfide (SnS) is a promising light-harvesting material for solar cell applications, owing to its potential for large-scale production, cost-effectiveness, eco-friendly source materials, and long-term stability. However, SnS crystallizes in an orthorhombic structure, which results in a highly anisotropic charge transport behavior. Tailoring the crystallographic orientation of the SnS absorber layer plays a critical role in the enhancement of the transfer of charge carriers and the power conversion efficiency (PCE). By controlling the substrate tilting angle and temperature ramp rate in vapor transport deposition, the crystal growth orientation was tuned to a preferred direction which significantly suppressed the unfavorable (040) crystallographic plane. Through the combination of these two approaches, the PCE could be increased from 0.11% to 2%. The effect of the tilting angle was numerically simulated to investigate its role in controlling the film uniformity and directing the film growth. In addition, the correlation between the texture coefficient of the (040) plane and the charge transport properties was determined by a combination of analytical methods such as device performance studies, electrochemical impedance spectroscopy, along with transient photovoltage, space-charge-limited current, and dark current measurements. These techniques were blended together to prove that the marked improvement in PCE can be ascribed to a reduced charge recombination (in both SnS bulk and interfaces) and an enhanced hole mobility.

Interfacial Engineering of PTAA/Perovskites for Improved Crystallinity and Hole Extraction in Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) have gained rapid progress and increasing research interest in recent years. The poly (triarylamine) (PTAA) is the most frequently used semiconductor in the hole-transporting layer (HTL) in inverted PSCs for its favorable highest occupied molecular orbital energy level (-5.2 eV), excellent carrier mobility, and low-temperature solution processability. However, its intrinsic hydrophobic property hinders the growth of high-quality perovskite on the PTAA film, which is one of the main obstacles that limits the further development of inverted PSCs. Herein, a donor-acceptor-donor type organic molecule, 4,4',4″-(1-hexyl-1H-dithieno [3',2':3,4; 2″,3″:5,6] benzo[1,2-d] imidazole-2,5,8-triyl) tris (N,N-bis(4-methoxyphenyl) aniline) (denoted as M2), is employed to modify the surface of PTAA. The PTAA/M2 composite hole transport layer facilitates the growth of perovskite films due to ameliorated hydrophobic property of PTAA. PTAA/M2 also exhibits enhanced hole mobility and conductivity than pristine PTAA. With enhanced crystallinity and hole extraction ability, using PTAA/M2 instead of pure PTAA as HTL, the power-conversion efficiency of inverted PSC increases from 18.67% to 20.23%. Furthermore, its operational stability is also enhanced. Our methodology carves out a novel path for addressing the hydrophobic issue of PTAA and improving the efficiency and photostability of inverted PSCs.

Synergetic Enhancement of Hole Mobility by Molecular Doping and Energy Band Modulation for Highly-Efficiency Perovskite Solar Cells

Synergetic Enhancement of Hole Mobility by Molecular Doping and Energy Band Modulation for Highly-Efficiency Perovskite Solar Cells

Phosphorene Nanoribbon-Augmented Optoelectronics for Enhanced Hole Extraction.

Phosphorene nanoribbons (PNRs) have been widely predicted to exhibit a range of superlative functional properties; however, because they have only recently been isolated, these properties are yet to be shown to translate to improved performance in any application. PNRs show particular promise for optoelectronics, given their predicted high exciton binding energies, tunable bandgaps, and ultrahigh hole mobilities. Here, we verify the theorized enhanced hole mobility in both solar cells and space-charge-limited-current devices, demonstrating the potential for PNRs improving hole extraction in universal optoelectronic applications. Specifically, PNRs are demonstrated to act as an effective charge-selective interlayer by enhancing hole extraction from polycrystalline methylammonium lead iodide (MAPbI3) perovskite to the poly(triarylamine) semiconductor. Introducing PNRs at the hole-transport/MAPbI3 interface achieves fill factors above 0.83 and efficiencies exceeding 21% for planar p-i-n (inverted) perovskite solar cells (PSCs). Such efficiencies are typically only reported for single-crystalline MAPbI3-based inverted PSCs. Methylammonium-free PSCs also benefit from a PNR interlayer, verifying applicability to architectures incorporating mixed perovskite absorber layers. Device photoluminescence and transient absorption spectroscopy are used to demonstrate that the presence of the PNRs drives more effective carrier extraction. Isolation of the PNRs in space-charge-limited-current hole-only devices improves both hole mobility and conductivity, demonstrating applicability beyond PSCs. This work provides primary experimental evidence that the predicted superlative functional properties of PNRs indeed translate to improved optoelectronic performance.

Fabrication of Ag embedded−SnS films via the RF approach: First study on NO2 gas–sensing performance

We report on the synthesis of 5-nm thick-Ag embedded−SnS (Ag/SnS) films by the radio frequency (RF) sputtering method as an absorbent layer to detect NO2 gas. Structure, morphology, elements, and optical properties of the Ag/SnS films were studied by X − ray diffraction, scanning electron microscopy, energy−dispersive spectroscopy, Raman and photoluminescence techniques, respectively. We firstly investigated the sensitivity of 5 – 20 ppm concentration of the Ag/SnS films to NO2 gas at an operating temperature ranging 30 – 100 °C. It was indicated that the Ag/SnS film–based sensor got good response and recovery at an operating temperature of 80 °C for NO2 gas. The 100 nm thick SnS film−based sensor made a faster response time (40 s) and recovery time (1320 s) to 20 ppm NO2 gas at 30 °C than those of other SnS films−based sensors. The result shows that the Ag/SnS film might be suitable for improving NO2 sensor properties due to the enhanced hole mobility, and more defectiveness of the SnS monolayer (Sn–vacancy). Based on these findings, we propose the fabrication of nanometals on SnS film for the high sensitive and selective NO2 gas−sensing a lower detection limit and at room temperature.

Gold atom diffusion assisted thermal healing enabling high-performance hole-transporting material in solar cells

The use of the compact hole-transporting layer (HTL) with strong hole extraction ability is vital to prepare high-efficiency solar cells. Here, we report the application of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) doped copper phthalocyanine (CuPc) as the hole-transporting layer for the Sb2(S,Se)3 solar cells. We find that the diffusion of gold atoms into the copper phthalocyanine film is able to heal the cracks and pinholes of the CuPc film, which enables the morphology to become more flat and denser, along with enhanced hole mobility. Benefitting from these results, the F4-TCNQ doped CuPc-based Sb2(S,Se)3 solar cells achieved best power conversion efficiency of 8.57%. More importantly, the device based on F4-TCNQ doped CuPc HTL showed essentially improved operational stability under the condition of 85% humidity and 85 °C. This research provides a suitable method for improving the morphology and transport properties of the CuPc based hole-transporting layer for solar cell and other optoelectronic device applications.

A Localized Planarization Strategy in Hole Mobility Modulation of Disordered Triphenylamine‐Based Organic Semiconductors

AbstractHole mobility plays a critical role in organic semiconductors, which is synergistically controlled by many factors closely interrelated to the molecular configuration, for example, the degree of molecular planarization. But at present, analysis from quantitative ab initio models to assess this correlation is lacking. Here, a series of triphenylamine‐based materials are designed and investigated to build a system with different levels of planarization. The key parameters in the Marcus equation are calculated with quantum and molecular mechanics methods and the hole mobilities are evaluated. Compared with non‐planar and fully planar molecules, localized planar molecules exhibit low reorganization energy, high transfer integral, and moderate energy disorder. Considering the conjugation and rigidity effects, a localized planarization strategy is demonstrated to design functional triphenylamine‐based materials by keeping a balance of the three factors above and enhanced hole mobilities are predicted. This strategy will shed light on mobility optimization and the applications of triphenylamine‐based materials.

Crystalline Domain Formation to Enable High-Performance Polymer Thermoelectrics Inspired by Thermocleavable Materials.

Improving the electrical conductivity is an important role in realizing high thermoelectric performance of solution-processable polymers. Herein, a simple and robust approach to boost the mobility and doping efficiency of a diketopyrrolopyrrole-based copolymer with the introduction of thermocleavable side chains (PDPPS-X, where X is the molar ratio of the thermocleavable side chains and alkyl chains) is first provided. Notably, the incorporated thermocleavable groups can be effectively removed after thermal treatment and therefore contribute to the crystalline domain formation via hydrogen-bonded networks, which is critical for conductivity enhancements. Grazing incidence wide-angle X-ray scattering (GIWAXS) patterns give a clear indication that the thermal treatment of PDPPS-5 can greatly improve the structural arrangement, resulting in a significantly enhanced hole mobility (5.4 times that of PDPPS-0 without thermocleavable chains). Compared to PDPPS-0, a larger Fermi level shift is observed after doping PDPPS-5 with FeCl3, reflecting a better doping efficiency. Consequently, remarkably improved conductivity and power factor are achieved by PDPPS-5 after doping with 0.03 M FeCl3 at room temperature, which are about 2.2 and 3.5 times higher than that of PDPPS-0 at the same testing condition, respectively. Moreover, PDPPS-5 achieved a maximum power factor of 57.5 μW m-1 K-2 at 404 K.

A Facile and Effective Ozone Exposure Method for Wettability and Energy-Level Tuning of Hole-Transporting Layers in Lead-Free Tin Perovskite Solar Cells.

Lead-free perovskite solar cells (PSCs) have attracted interest among scientists searching for eco-friendly energy harvesting devices. Herein, the effects of ozone exposure on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in lead-free tin halide PSCs as a facile and low-cost process for improving device performance are analyzed. Two types of tin-based PSCs and one typical lead-based PSC were fabricated. The ozone exposure on PEDOT:PSS increases the short-circuit current density (JSC) and the fill factor (FF) of PSCs in all cases with perovskite grain enlargement and hole-mobility enhancement of the devices, respectively. For open-circuit voltage (VOC), the outcome depends on the band gap and the energy levels of the perovskite films. While ozone exposure treatment is favorable for PEA0.15FA0.85SnI3-based tin PSCs, VOC decreases with ozone exposure in the case of Ge:EDA0.01FA0.98SnI3-based tin PSCs because of a misalignment of the energy levels. Regardless, the efficiency of PEA0.15FA0.85SnI3-based tin PSCs increases from 8.7 to 10.1% when measured inside a glovebox upon ozone exposure of PEDOT:PSS. The efficiency of Ge:EDA0.01FA0.98SnI3-based tin PSCs increases from 6.8 to 8.1%, and the devices retain an efficiency of 5.0% even after 50 days in air.

Site-Selective Oxygen Vacancy Formation Derived from the Characteristic Crystal Structures of Sn–Nb Complex Oxides

Divalent tin oxides have attracted considerable attention as novel p-type oxide semiconductors, which are essential for realizing future oxide electronic devices. Recently, p-type Sn2Nb2O7 and SnNb2O6 were developed; however, an enhanced hole mobility by reducing defect concentrations is required for practical use. In this work, we investigated the correlation between the formation of oxygen vacancy (VO··), which may reduce the hole-generation efficiency and hole mobility, and the crystal structure in Sn–Nb complex oxides. Extended X-ray absorption fine structure spectroscopy and a Rietveld analysis of X-ray diffraction data revealed the preferential formation of VO·· at the O site bonded to the Sn ions in both the tin niobates. Moreover, a larger amount of VO·· around the Sn ions was found in the p-type Sn2Nb2O7 than in the p-type SnNb2O6, indicating the effect of VO·· on the low hole-generation efficiency. To elucidate the dependence of the formation of VO·· on the crystal structure, we evaluated the Sn–O bond strength based on the bond valence sum and Debye temperature. The differences in the bond strengths of the two Sn–Nb complex oxides are correlated through the steric hindrance of Sn2+ with an asymmetric electron density distribution. This suggests the importance of the material design with a focus on the local structure around the Sn ions to prevent the formation of VO·· in p-type Sn2+ oxides.

Toward Unusual-High Hole Mobility of p-Channel Field-Effect-Transistors.

The relative low hole mobility of p-channel building block device challenges the continued miniaturization of modern electronic chips. Metal-semiconductor junction is always an efficient strategy to control the carrier concentration of channel semiconductor, benefiting the carrier mobility regulation of building block device. In this work, complementary metal oxide semiconductor (CMOS)-compatible metals are selected to deposit on the surface of the important p-channel building block of GaSb nanowire field-effect-transistors (NWFETs), demonstrating the efficient strategy of hole mobility enhancement by metal-semiconductor junction. When deposited with lower work function metal of Al, the peak hole mobility of GaSb NWFET can be enhanced to as high as ≈3372 cm2 V-1 s-1 , showing three times than the un-deposited one. The as-studied metal-semiconductor junction is also efficient for the hole mobility enhancement of other p-channel devices, such as GaAs NWFET, GaAs film FET, and WSe2 FET. With the enhanced mobility, the as-constructed CMOS inverter shows good invert characteristics, showing a relatively high gain of ≈18.1. All results may be regarded as important advances to the next-generation electronics.

Highly Efficient Ternary Solar Cells with Efficient Förster Resonance Energy Transfer for Simultaneously Enhanced Photovoltaic Parameters

AbstractIntroducing a third component into organic bulk heterojunction solar cells has become an effective strategy to improve photovoltaic performance. Meanwhile, the rapid development of non‐fullerene acceptors (NFAs) has pushed the power conversion efficiency (PCE) of organic solar cells (OSCs) to a higher standard. Herein, a series of fullerene‐free ternary solar cells are fabricated based on a wide bandgap acceptor, IDTT‐M, together with a wide bandgap donor polymer PM6 and a narrow bandgap NFA Y6. Insights from the morphological and electronic characterizations reveal that IDTT‐M has been incorporated into Y6 domains without disrupting its molecular packing and sacrificing its electron mobility and work synergistically with Y6 to regulate the packing pattern of PM6, leading to enhanced hole mobility and suppressed recombination. IDTT‐M further functions as an energy‐level mediator that increases open‐circuit voltage (VOC) in ternary devices. In addition, efficient Förster resonance energy transfer (FRET) between IDTT‐M and Y6 provides a non‐radiative pathway for facilitating exciton dissociation and charge collection. As a result, the optimized ternary device features a significantly improved PCE up to 16.63% with simultaneously enhanced short‐circuit current (JSC), VOC, and fill factor (FF).