Deep Energy Levels Research Articles

Synthesis of Bithiazole-Based Poly(arylenevinylene)s via Co-Catalyzed Hydroarylation Polyaddition and Tuning of Their Optical Properties by N-Methylation and N-Oxidation.

Bithiazole-based poly(arylenevinylene) is synthesized via the Co-catalyzed hydroarylation polyaddition of N,N,N',N'-tetrahexyl-(2,2'-bithiazole)-4,4'-dicarboxamide with 2,7-diethynyl-9,9-bis(2-ethylhexyl)fluorene in a regioselective manner. The introduction of the 2,2'-bithiazole unit deepens the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the polymer compared to the analogous bithiophene-based poly(arylenevinylene). N-Methylation and N-oxidation of the thiazole moiety further deepen the HOMO and LUMO energy levels of the polymer, which is attributed to the enhanced electron-withdrawing effect. The N-oxidized polymer exhibits a high photoluminescence quantum yield and serves as an emitting material in an organic light-emitting diode, and its deep HOMO energy level efficiently restrains the trapping of holes in the host poly(vinylcarbazole) matrix.

Modulation of Molecular Quadrupole Moments by Phenyl Side-Chain Fluorination for High-Voltage and High-Performance Organic Solar Cells.

The ground-state charge generation (GSCG) in photoactive layers determines whether the photogenerated carriers occupy the deep trap energy levels, which, in turn, affects the device performance of organic solar cells (OSCs). In this work, charge-quadrupole electrostatic interactions are modulated to achieve GSCG through a molecular strategy of introducing different numbers of F atom substitutions on the BTA3 side chain. The results show that 8F substitution (BTA3-8F) and 16F substitution (BTA3-16F) lead to different patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy level changes. The perfluorination of the phenyl side chain endows BTA3-16F with a LUMO energy level similar to that of BTA3, ensuring a high VOC. Besides, BTA3-16F features a large charge-quadrupole moment, promoting strong electrostatic interactions between neighboring molecules along the π-π stacking direction, which then induces the GSCG in photoactive components. This efficient GSCG directly makes a significant impact on the subsequent kinetics of photogenerated exciton dissociation, recombination, and transport over longer time periods, as well as on nonradiative recombination over larger spatial scales. Benefiting from the favorable GSCG and suitable energy level arrangement, PTQ10/BTA3-16F achieves a VOC of 1.302 V and a PCE of 11.14%, setting the world record for OSCs performance with a VOC greater than 1.3 V. In addition, BTA3-16F is an effective guest molecule to improve the performance of ternary OSCs, and PM6/L8-BO/BTA3-16F-based ternary device achieves the highest PCE of 19.82%. This result emphasizes the important role of GSCG between photoactive components in OSC performance and demonstrates that modulation of molecular quadrupole moments is an effective means of designing efficient acceptors.

Current Mechanisms in Zinc Diffusion-Doped Silicon Samples at T = 300 K

This work is devoted to the study of current flow in diffusion-doped zinc silicon samples in the dark and when illuminated with light with an intensity in the range from 0.6 to 140 lx and at a temperature of 300 K. At T = 300 K and in the dark, the type of the I–V characteristic contained all areas characteristic of semiconductors with deep energy levels. It was found that when illuminated with light, the type of I–V characteristics of the studied Si samples depended on the value of the applied voltage, the electrical resistivity of the samples, the light intensity, and their number reached up to 6. In this case, linear, sublinear, and superlinear sections were observed, as well as the switching point (sharp current jump) and areas with negative differential conductivities (NDC). The existence of these characteristic areas of the applied voltage and their character depended on the intensity of the light. The experimental data obtained were interpreted in the formation of low dimensional objects with the participation of multiply charged zinc nanoclusters in the bulk of silicon. They changed the energy band structure of single-crystal silicon, which affected generation-recombination processes in Si, leading to the types of I–V characteristics observed in the experiment.

Mechanism of Current Performance in Thin-Film Heterojunctions n-CdS/p-Sb2Se3 Obtained by the CMBD Method

In this work, we analyzed the temperature dependence of the current-voltage characteristics of the structure of glass/Mo/p-Sb2Se3/n-CdS/In. From an analysis of the temperature dependences of the direct branches of the I-V characteristic of the heterojunction, it was established that the dominant mechanism of current transfer at low biases (3kT/e<V<0.8V) is multi-stage tunneling-recombination processes involving surface states at the Sb2Se3/CdS interface. At V>0.8 V, the dominant current transfer mechanism is Newman tunneling. In the case of reverse bias (3kT/e<V<1.0 eV), the main mechanism of charge carrier transfer through a heterojunction is tunneling through a potential barrier involving a deep energy level. At higher reverse voltages, a soft breakdown occurs.

Gradient Mo1−xWxSe2 monolayer alloys: Synthesis and multifunctional applications

With the continuous and rapid development of electronic information technology, the demand for new materials with miniaturization, high integration, high performance, and multifunction is becoming increasingly urgent. However, it is difficult for existing photodetectors based on a single material to achieve multi-functionality while maintaining excellent performance, and the devices based on heterostructures are faced with complex preparation and compatibility problems. In this work, gradient Mo1−xWxSe2 monolayer alloys with high crystal quality have been synthesized by an evaporation-assisted chemical vapor deposition method. The composition of the synthesized Mo1−xWxSe2 monolayer alloys varies gradually with x ranging from 0 to 1. The Mo1−xWxSe2 based photodetector shows superior photoresponse performance in the visible wavelength with maximum responsivity of 26 A/W and external quantum efficiency up to 6320 % under 520 nm laser irradiation. Besides, the Mo1−xWxSe2 device is capable of high-resolution imaging, which can be used as image sensor. Moreover, nonvolatile memory function has also been realized in the device because the band gap of Mo1−xWxSe2 can be effectively adjusted by the gradient distribution of the component and the deep energy levels caused by Se vacancies can be modulated to shallow energy levels. A thrilling discovery is that the gradient Mo1−xWxSe2 alloy device can simulate the biological synapses successfully, including paired-pulse facilitation, short-term plasticity, long-term plasticity and learning process. The realization of high-performance photodetection, visualization, nonvolatile memory and synaptic simulation based on a single gradient crystal offers a new type of material to develop advanced optoelectronic devices with multiple functions.

Metal chalcogenide electron extraction layers for nip-type tin-based perovskite solar cells

Tin-based perovskite solar cells have garnered attention for their biocompatibility, narrow bandgap, and long thermal carrier lifetime. However, nip-type tin-based perovskite solar cells have underperformed largely due to the indiscriminate use of metal oxide electron transport layers originally designed for nip-type lead-based perovskite solar cells. Here, we reveal that this underperformance is caused by oxygen vacancies and deeper energy levels in metal oxide. To address these issues, we propose a metal chalcogenide electron transport layer, specifically Sn(S0.92Se0.08)2, which circumvents the oxygen molecules desorption and impedes the Sn2+ oxidation. As a result, tin-based perovskite solar cells with Sn(S0.92Se0.08)2 demonstrate a VOC increase from 0.48 – 0.73 V and a power conversion efficiency boost from 6.98 – 11.78%. Additionally, these cells exhibit improved stability, retaining over 95% of their initial efficiency after 1632 h. Our findings showcase metal chalcogenides as promising candidates for future nip-type tin-based perovskite solar cell applications.

Study of the effect of CdCl2 introduction on the high temperature activation treatment of CdTe:As polycrystalline thin films

V-doped CdTe polycrystalline films can achieve both doping activation and defect passivation by high-temperature CdCl2 heat treatment, but this requires simultaneous modulation of the amount of CdCl2 introduced to obtain high-quality films. It is found that increasing the CdCl2 introduction does not change the physical phase structure and lattice constant of CdTe:As thin films, but promotes grain recrystallisation, and can promote the formation of A-center, and inhibit the formation of Cd vacancy (VCd) defects, as well as the formation of deep energy level defects. The results provide guidance for the improvement of high-temperature CdCl2 heat treatment of V-doped CdTe polycrystalline thin films.

Oxidative Passivation of FAPbI3 via Femtosecond Laser for Enhanced Photoluminescence and Photoresponse Performance

AbstractThe presence of uncoordinated Pb atoms in perovskite materials, acting as non‐radiative recombination centers, significantly degrades the performance of perovskite‐based photoelectronic devices. Addressing this issue by passivating these deep energy level defects is essential for enhancing device performance. By now, the passivation methods are largely proposed by chemical additive engineering methods, which involve the oxidation of Pb through chemical additives. However, chemical passivation methods are often plagued by issues such as prolonged processing times, uncontrollable passivation regions uncontrollable, and environmental contamination. Here, a novel femtosecond laser oxidative passivation (FsLOP) technique for FAPbI3 is proposed, evidenced by X‐ray photoelectron spectroscopy (XPS) revealing the formation of Pb─O bonds. The role of peroxide anions in oxidation passivation is highlighted as pivotal. The oxidative passivation effect is further corroborated by a four‐fold increase in photoluminescence (PL) intensity and an exceptional improvement in photoresponse performance, achieving a detectivity of 6.77 × 1012 Jones. This work provides a deeper insight into the interaction between femtosecond lasers and perovskite materials, proposing an efficient, precisely controlled, and environmentally friendly way to improve the performance of perovskite photoelectronic devices.

Efficient Derivatization of a Thienobenzobisthiazole-Based π-Conjugated Polymer Through Late-Stage Functionalization Towards High-Efficiency Organic Photovoltaic Cells.

Derivatization is essential for optimizing organic material properties. However, because functional groups are often introduced at an early stage of the synthesis, similar intermediates have to be repeatedly synthesized to produce derivatives, which amounts to a daunting and time-consuming task. Using thienobenzobisthiazole (TBTz) as a building unit of donor polymers for organic photovoltaics (OPVs), we demonstrate an efficient derivatization of a TBTz-based π-conjugated polymer by late-stage functionalization. In the developed synthetic route, functional groups are introduced at the last step of monomer synthesis, enabling us to easily synthesize several derivatives from a common intermediate. Ester and acyl groups are introduced into the polymer instead of the alkyl group, giving rise to deep HOMO energy levels and resulting in OPV cells with high open-circuit voltage even in the absence of halogen substituents that are typically introduced into the donor polymers. Notably, the ester-functionalized TBTz-based polymer shows a small nonradiative voltage loss (ΔVnr) of 0.19 V and has one of the highest charge generation efficiencies among the halogen-free donor polymers with similar ΔVnr, improving the critical trade-off relationship between voltage loss and charge generation. Our results provide an important guideline for the efficient development of high-performance polymers for OPVs.

Efficient Derivatization of a Thienobenzobisthiazole‐Based π‐Conjugated Polymer Through Late‐Stage Functionalization Towards High‐Efficiency Organic Photovoltaic Cells

AbstractDerivatization is essential for optimizing organic material properties. However, because functional groups are often introduced at an early stage of the synthesis, similar intermediates have to be repeatedly synthesized to produce derivatives, which amounts to a daunting and time‐consuming task. Using thienobenzobisthiazole (TBTz) as a building unit of donor polymers for organic photovoltaics (OPVs), we demonstrate an efficient derivatization of a TBTz‐based π‐conjugated polymer by late‐stage functionalization. In the developed synthetic route, functional groups are introduced at the last step of monomer synthesis, enabling us to easily synthesize several derivatives from a common intermediate. Ester and acyl groups are introduced into the polymer instead of the alkyl group, giving rise to deep HOMO energy levels and resulting in OPV cells with high open‐circuit voltage even in the absence of halogen substituents that are typically introduced into the donor polymers. Notably, the ester‐functionalized TBTz‐based polymer shows a small nonradiative voltage loss (ΔVnr) of 0.19 V and has one of the highest charge generation efficiencies among the halogen‐free donor polymers with similar ΔVnr, improving the critical trade‐off relationship between voltage loss and charge generation. Our results provide an important guideline for the efficient development of high‐performance polymers for OPVs.

Enhancing insulating properties of glass-fiber reinforced polymers using plasma fluorination-modified boron nitride nanosheets

The insulation failure of glass fiber-reinforced polymers (GFRP) limits their use in high-voltage insulation fields. In this study, boron nitride nanosheets (BNNS) were prepared using ball-milling and further fluorinated via dielectric barrier discharge (DBD) plasma treatment. The GFRP nanocomposites were fabricated using different filler types and doping concentrations. The test results indicated that fluorinated BNNS (F-BNNS) displays good dispersion and interfacial compatibility, enhances the interfacial bonding strength of the “fiber-matrix-filler” ternary system in GFRP, and reduces the internal defects of materials. In addition, the insulating properties of the composites were related to the filler concentration. Adding a trace amount of F-BNNSs increased the flashover and breakdown voltages of the GFRP by up to 28.77% and 21.62%, respectively. The results of molecular dynamics simulations and trap distribution calculations showed that plasma fluorination of BNNS increases the bandgap and deep trap energy level at the interface. The extremely strong charge-binding ability of the deep traps inhibits continuous charge injection and regulates carrier migration, which improves the insulating properties of the composites. The results of this study provide a novel, environmentally friendly, and efficient solution for improving the insulating properties of GFRP.

A novel high-resolution technique for the study of deep energy levels in semiconductors based on computerized Laplace-DLTS

This paper describes a new computerized system for investigating deep levels in semiconductors by DLTS. We used a modified measurement mode, a new approach based on the inverse Laplace transform, and a new data processing algorithm. The developed method uses only a few transients derived and averaged from DLTS measurements at heating rates up to 2 °C/min, combined with low-frequency pulses. The paper presents data obtained for a phosphorus-doped silicon PIN diode, previously investigated using a conventional computerized DLTS system. Our new method allowed us to detect three electronic levels with energies of Ec – 0.53 eV, Ec – 0.39 eV, and Ec – 0.38 eV in less than 1 h, while the conventional DLTS system detected only two levels: Ec – 0.53 eV and Ec – 0.42eV. Thus, we have shown that the new approach drastically reduces the measurement time and increases the resolution.

Synergistic Effects of Surface States and Deep Energy Level Traps on InGaAs p-i-n Diodes under Proton Irradiation

Synergistic Effects of Surface States and Deep Energy Level Traps on InGaAs p-i-n Diodes under Proton Irradiation

Homogenizing Energy Landscape for Efficient and Spectrally Stable Blue Perovskite Light-Emitting Diodes.

Blue perovskite light-emitting diodes (PeLEDs) have attracted enormous attention; however, their unsatisfactory device efficiency and spectral stability still remain great challenges. Unfavorable low-dimensional phase distribution and defects with deeper energy levels usually cause energy disorder, substantially limiting the device's performance. Here, an additive-interface optimization strategy is reported to tackle these issues, thus realizing efficient and spectrally stable blue PeLEDs. A new type of additive-formamidinium tetrafluorosuccinate (FATFSA) is introduced into the quasi-2D mixed halide perovskite accompanied by interface engineering, which effectively impedes the formation of undesired low-dimensional phases with various bandgaps throughout the entire film, thereby boosting energy transfer process for accelerating radiative recombination; this strategy also diminishes the halide vacancies especially chloride-related defects with deep energy level, thus reducing nonradiative energy loss for efficient radiative recombination. Benefitting from homogenized energy landscape throughout the entire perovskite emitting layer, PeLEDs with spectrally-stable blue emission (478nm) and champion external quantum efficiency (EQE) of 21.9% are realized, which represents a record value among this type of PeLEDs in the pure blue region.

Sn2+/Pb2+ Doping‐Induced Highly Transparent Boroaluminate Microcrystalline Glass With Deep Traps for Long‐Term Optical Storage and Time‐Lapse X‐ray Imaging

AbstractThe development of microcrystalline glass‐ceramics with high transparency and deep trap energy levels is crucial for the cost‐effective and large‐scale production of scintillators and optical data storage applications. In this study, the incorporation of highly electronegative divalent tin (Sn2+) plays a key role in modulating the network structure of borate glass. This leads to the successful synthesis of SrAl2O4:Eu2+ microcrystalline glass with high transparency, reaching up to 80%, and excellent crystallinity. Additionally, a series of non‐optically active ions with different valence states is co‐doped with Eu2+ to fine‐tune the trap levels of the SrAl2O4 microcrystals. All samples maintain high crystallinity and exhibit good transparency. In particular, the Pb2+ ion co‐doped samples achieve an increased trap energy level of 1.28 eV, significantly enhancing their capacity to capture X‐rays and ultraviolet light. Density functional theory calculations reveal that this enhancement is due to severe lattice distortion caused by Pb2+ ions occupying interstitial sites in SrAl2O4. Utilizing the SrAl2O4:Eu2+, Pb2+ glass‐ceramics materials, X‐ray imaging with a delay of up to 210 s and optical information storage for >60 d is achieved. This study provides valuable insights into the crystal growth and trap modulation of persistent luminescent materials within a three‐dimensional glass network structure.

Comparative Analysis of 50 MeV Li3+ and 100 MeV O7+ Ion Beam Induced Electrical Modifications in Silicon Photodetectors

This article investigates the impact of 100 MeV O7+ and 50 MeV Li3+ ions on Silicon Photodetectors, focusing on their electrical characteristics with similar Sn/Se ratios. Elevated ion fluences led to a significant rise in the ideality factor “n”, indicating the presence of Generation-Recombination (G-R) current due to introduced defects, especially those with deep energy levels in the forbidden gap acting as G-R centers. While Ideality factor (n) values decreased for oxygen ions at maximum fluence, they increased for lithium ions, reflecting consistent patterns in series resistance (Rs) and reverse leakage current (IR), attributed to ion-induced defects. Oxygen ions showed a monotonic variation in Rs, whereas lithium ions exhibited a slight reduction at maximum fluence, possibly due to defect annihilation. Despite differing Se values, 50 MeV Li3+ ions demonstrated improved device characteristics, suggesting potential defect annihilation. The ratio of Sn to Se indicated comparable damage contributions from nuclear and electronic energy. Additionally, TRIM computations revealed non-uniform damage distributions, with ions penetrating deep into the substrate, away from the n+/p junction.

Behavior of defects in GaN avalanche photodiodes grown on GaN substrates

GaN avalanche photodiodes grown on GaN substrates were successfully fabricated. These devices displayed a low dark current, measuring <80 pA at a reverse bias of 82.0 V. Notably, the response spectrum of the devices showed new out-of-band response peaks with increasing reverse bias. Moreover, at high reverse bias, the devices emitted visible light. These phenomena were attributed to inherent defects within the materials. The defect level fitted from the tunneling currents closely matched the experimental value, indicating that the defect-assisted tunneling effect, with a defect level at 0.127 eV relative to the conduction band, contributed to the out-of-band response peak in the response spectrum. The Franz–Keldysh effect led to a redshift in the response spectrum. Additionally, the Mg-related deep energy level situated approximately 0.498 eV above the valence band, facilitated radiative recombination at high reverse bias. Meanwhile, the device’s luminescent image displayed a consistently square shape, suggesting uniform avalanche breakdown throughout the device.

Enhanced High-Temperature performance of PEI dielectrics via deep trap energy levels and physically crosslinked effects

Dielectric capacitors are indispensable energy storage components in both civilian applications and industrial processes. Under elevated temperatures and intense electric fields, polymer dielectrics usually suffer from an inevitably increase in conductivity, leading to a significant reduction in breakdown strength, energy density and efficiency. This investigation aims to design an all-organic dielectric with enhanced high-temperature capacitive performance by introducing a small molecule P-xylene F (PF) into polyetherimide (PEI). Two mechanisms including the incorporation of deep trap energy levels via wide bandgap fillers and the electrostatic interactions by hydrogen bonding between the fillers and the polymer matrix are proposed to support the enhancement. The hydrogen bonding between PF and polyamic acid (PAA)chains induces the formation of physical cross-linking between PF and the negatively charged benzene rings in PEI after imidization. This influences benzene ring stacking within the polymer chains and enhances the film’s mechanical strength. Additionally, PF’s wider bandgap compared to PEI introduces deep trap energy levels, hindering carrier transport and reducing conductive losses at high temperatures. As results, the dielectric achieves an energy density (Ud) of 4.47 J/cm3 with an efficiency (η) above 90 % at 200 °C. Its excellent stability is also demonstrated with over 210,000 charge–discharge cycles at 200 °C. This study promotes the development of high-performance dielectrics at high temperature.

Over 10% efficient Cu2ZnSn(S, Se)4 Thin-Film cells prepared by aluminium doping

Cu2ZnSn(S,Se)4(CZTSSe) solar cell is of excellent development tendency because of lower pollution and outstanding power conversion efficiency(PCE). Yet, current PCE of CZTSSe is limited because of a high open-circuit voltage deficit, primarily put down to severe band tailing and carrier recombination. In this paper, absorber films were obtained by solution method and the influences of different aluminum doping concentrations on the properties of CZTSSe thin film cell were studied. Analysis about X-ray diffraction (XRD) and Raman spectroscopy confirms which Al has incorporated into CZTSSe thin film lattice and replaced Sn. Hall effect measurements reveal the improvement of carrier concentration on thin film absorber layer attribute to the formation of AlSn acceptor defects. Furthermore, X-ray photoelectron spectroscopy (XPS) reveals that Al enter into the CZTSSe lattice and Al is in the appropriate state of + 3 valence without generating additional harmful defects. More important, the generation of deep energy level defects and defect clusters associated with Sn were suppressed by replacing Sn with Al. Finally, the photovoltaic performance of different Al doped CZTSSe cells were characterized by conducting J-V and external quantum efficiency (EQE) tests. Remarkably, the CZTSSe solar cell with PCE as high as 10.59 % is obtained under a doping level of 6 % Al, which has an open circuit voltage of 522 mv. Compared with reference CZTSSe solar cells with an efficiency of 7.29 %, which indicates with improvement of 45 % in efficiency. Consequently, Al doping process is considered as a prospective tactic to elevate the PCE of CZTSSe solar cells.

Scalable polyolefin-based all-organic dielectrics with superior high-temperature capacitive energy storage performance

Polymer dielectrics capable of efficient and stable operation at elevated temperatures (>150 °C) are urgently needed to meet the stringent requirements of capacitive energy storage in harsh environments. However, the current leading commercially available polymer dielectric, biaxially oriented polypropylene (BOPP), can only sustain continuous operation at temperatures below 85 °C due to its limited thermal stability and significant increase in electrical conduction at high temperatures. Here, we present an all-organic polymer composite comprising nonpolar polyolefin and organic semiconductor that demonstrates superior dielectric and capacitive energy storage performance at 150 °C. Notably, the dielectric properties of the polymer composite remain stable across a broad temperature range, exhibiting an ultralow dissipation factor at elevated temperatures. Benefiting from the deep trap energy levels introduced by the organic semiconductor, the composite film achieves one order of magnitude reduction in electrical conductivity. As a result, the composite film attains discharged energy densities of 7.1 J/cm3 and 5.5 J/cm3 with a charge-discharge efficiency of 90 % at 25 °C and 150 °C, respectively. Furthermore, the composite film maintains stable capacitive performance over extended charge-discharge cycles (50,000 cycles) in harsh environments (500 MV/m and 150 °C), along with excellent breakdown self-healing capability. These remarkable performances, coupled with the potential for large-scale production using commercially available raw materials, highlight the practically viability of the composite film for high-temperature capacitive energy storage applications.