Acceptor Energy Level Research Articles

Stability Properties of Inverted Organic Solar Cells Prepared with a ZnO Buffer Layer

Organic solar cells (OSCs) of inverted structure (IOSC) were designed to enhancement the solar cell efficiency and stability in organic based solar cell. IOSC was built with the structure of Au/P3HT:PCBM/ZnO/ITO. ZnO thin layers were fabricated on ITO electrodes using the unbalanced magnetron sputtering method. ZnO layer is used as the buffer layer in this structure to prevent oxidation by UV light to the interface of the organic layer and reduce the energy barrier, allowing electron to be easily transferred between the ITO energy level and the organic acceptor energy level (LUMO). ZnO films are also used as a barrier layer to prevent hole injection from P3HT due to the lack of charge carrier recombination. XRD results exhibited that the particle size in ZnO layers increased as the substrate temperature increased. The conversion efficiency of IOSC improved with increasing ZnO substrate temperature. Moreover, compared to the existing device, the IOSC using a ZnO buffer layer was in a stable state for a longer period of time. After about 7 days, it woas found that the Voc of the hybrid solar cells remained almost constant over time and under all conditions. As a result, the ZnO film in the OSC plays an important role for protecting the organic layer of OSCs and enhancing the efficiency.

Charge engineering in black phosphorene with tunable electronic structures as efficient oxygen evolution electrocatalyst

The unique electronic structure of layered black phosphorus (BP) makes it an ideal candidate material for electrocatalytic oxygen evolution reaction (OER). Charge doping effectively improves the environmental stability and catalytic activity of BP by providing electron transfer channels and reducing charge transfer barrier. Therefore, based on the first principles calculation, this paper theoretically discusses how the intrinsic charge doping without introducing impurities changes the electronic structure and improves the catalytic activity of BP. It is found that charge engineering can effectively regulate and change the electronic structure and work function by stimulating the hybridization between different P-p orbitals, while maintaining the direct bandgap semiconductor characteristics of monolayer BP system. More importantly, in the catalytic process of OER, electrons and hole doping as free charges provide different donor and acceptor energy levels for the system depending on the doping concentration, and affect the adsorption capacity of monolayer BP to different reaction intermediates. At a certain doping concentration, the carrier mobility increases significantly, and the optimal Gibbs free energy and overpotential can be achieved in monolayer BP. These results provide new opportunities and possibilities for designing charge-engineered BP catalysts with adjustable electronic structure and excellent OER activity.

Effects of Cp2Mg molar flow rate on structural, optical, and electrical properties of semipolar Mg-doped p-AlGaN epi-layers

The semipolar (11 2‾ 2) plane Mg-doped p-Al0.42Ga0.58N epi-layers were successfully deposited on (10 1‾ 0) m-plane sapphire substrates with metal organic chemical vapor deposition technology. The effects of Cp2Mg molar flow rate on the structural, optical, and electrical properties of p-Al0.42Ga0.58N epitaxial layer were extensively studied. The randomly distributed Mg atoms and/or clusters that partially covered the growth surface were verified to act as an island-like mask to block the propagation of dislocations along the growth direction, resulting in a significant improvement in the crystalline quality of the semipolar Mg-doped p-AlGaN epi-layers. Moreover, two emission peaks with novel behavior were observed in the photoluminescence spectrum and identified to be originated from the transition between the conduction band and the Mg-related shallow acceptor energy level, and the deep Mg-induced compensation donor and the Mg acceptor pair-related transition, respectively. In addition, a hole concentration as high as 1.03 × 1017 cm−3 and a resistivity as low as 12.8 Ω cm were achieved for the semipolar Mg-doped p-Al0.42Ga0.58N epi-layer grown with the optimized Cp2Mg molar flow rate in this study.

Charge transport and extrinsic absorption of two-dimensional defect-rich ZnIn2S4 semiconductor for below-bandgap photodetection

As a rediscovered ternary two-dimensional (2D) material, defect-rich Znln2S4 has great potential for energy-harvesting applications. However, the effect of defects on its physical properties and device performance remains elusive. Herein, we explored the influence of defects (S vacancies and In–Zn substitutions) in few-layer Znln2S4 on the charge transport and photoelectric performance. It is demonstrated that the defect-rich Znln2S4 device exhibits two-dimensional variable range hopping transport mechanism, with uniform charge transport along the channel and low contact resistance at the electrical contacts of Znln2S4/Au. Importantly, due to the contribution of the donor and acceptor energy levels inside the bandgap, the flake exhibits pronounced extrinsic absorption, leading to the competitive photodetector performance under sub-bandgap photo-excitation. Explicitly, the device exhibits a maximum responsivity of 4.08 × 104 A W−1, a photo-gain of >108 electrons per photon, and a specific detectivity of ∼1015 Jones under 532 nm laser excitation, with detection wavelength extending from 400 to 980 nm. Our findings underscore the significant potential of defect-engineering to enrich the functionalities of 2D semiconductors.

Data Cleansing and Sub-Unit-Based Molecular Description Enable Accurate Prediction of The Energy Levels of Non-Fullerene Acceptors Used in Organic Solar Cells.

Non-fullerene acceptors (NFAs) have recently emerged as pivotal materials for enhancing the efficiency of organic solar cells (OSCs). To further advance OSC efficiency, precise control over the energy levels of NFAs is imperative, necessitating the development of a robust computational method for accurate energy level predictions. Unfortunately, conventional computational techniques often yield relatively large errors, typically ranging from 0.2 to 0.5 electronvolts (eV), when predicting energy levels. In this study, the authors present a novel method that not only expedites energy level predictions but also significantly improves accuracy , reducing the error margin to 0.06eV. The method comprises two essential components. The first component involves data cleansing, which systematically eliminates problematic experimental data and thereby minimizes input data errors. The second component introduces a molecular description method based on the electronic properties of the sub-units comprising NFAs. The approach simplifies the intricacies of molecular computation and demonstrates markedly enhanced prediction performance compared to the conventional density functional theory (DFT) method. Ourmethodology will expedite research in the field of NFAs, serving as a catalyst for the development of similar computational approaches to address challenges in other areas of material science and molecular research.

High Luminescence in Layered Double Perovskite via Formation of Terbium Intercalation Complex

AbstractAs the field of perovskite emerges, doping presents an optimistic way to upgrade the functionalities of these materials and improve the photoluminescence quantum yield (PLQY). While doping is well‐explored in perovskites, it has received less attention in layered double perovskites (LDPs). Doping with lanthanides is particularly interesting for these wide bandgap materials because of their narrow and intense luminescence spectra. Here, the doping of (PEA)4NaInCl8 LDP (PEA = Phenylethylammonium) with Tb3+ and complex of Tb3+ with hexafluoroacetylacetonate (hfa) is studied, i.e., tetrakis β‐diketonate complex. In both cases, energy transfer from host to dopant leading to photoluminescence (PL) emission due to Tb3+ f‐f transitions is observed. However, in the case of Tb3+ doping, sensitization is not very efficient due to the nonideal alignment of energy levels of the host and resonance acceptor energy levels of Tb3+. Whereas, doping of (PEA)4NaInCl8 with Tb3+ in the form of hfa complex, provides a more ideal energetic environment for the efficient energy transfer from host to Tb3+ in the LDP matrix, resulting in a 20‐fold enhancement in the luminescence efficiency. The doping of Tb3+ and Tb3+ complex in LDP sets the foundation for a new approach for the synthesis of LDPs‐lanthanide host‐guest systems for high PLQY.

Laser doping of n-type 4H-SiC with boron using solution precursor for mid-wave infrared optical properties

Laser doping of n-type 4H-silicon carbide (SiC) semiconductor substrates with boron (B) using a pulsed Nd:YAG laser (λ = 1064 nm) is reported. An aqueous boric acid solution was used as a boron precursor. A simple theoretical heat transfer model was employed to select the laser processing parameters, i.e., laser power and laser-substrate interaction time, and determine the appropriate temperature to dope 4H-SiC substrates. The selected processing parameters ensured that the temperature at the laser-substrate interaction zone was below the SiC peritectic temperature to prevent any crystalline phase transformations in SiC. Fourier-transform infrared spectrometry was conducted to determine the optical properties of both undoped and boron-doped 4H-SiC substrates within the mid-wave infrared (MWIR) wavelength range (3–5 μm). Boron atoms create an acceptor energy level at 0.29 eV above the valence band in the 4H-SiC bandgap, which corresponds to λ = 4.3 μm. Boron-doped 4H-SiC substrate exhibited reduced reflectance and increased absorptance for the MWIR range. An absorption peak at λ = 4.3 μm was detected for the doped substrate. This confirmed the creation of the acceptor energy level in the 4H-SiC bandgap and, thus, doping of 4H-SiC with boron. A notable decrease in the refractive index, i.e., from 2.87 to 2.52, after laser doping of n-type 4H-SiC with boron was achieved.

Defect Emission and Its Dipole Orientation in Layered Ternary Znln2 S4 Semiconductor.

Defect engineering is promising to tailor the physical properties of 2D semiconductors for function-oriented electronics and optoelectronics. Compared with the extensively studied 2D binary materials, the origin of defects and their influence on physical properties of 2D ternary semiconductors are not clarified. Here, the effect of defects on the electronic structure and optical properties of few-layer hexagonal Znln2 S4 is thoroughly studied via versatile spectroscopic tools in combination with theoretical calculations. It is demonstrated that the Zn-In antistructural defects induce the formation of a series of donor and acceptor energy levels and sulfur vacancies induce donor energy levels, leading to rich recombination paths for defect emission and extrinsic absorption. Impressively, the emission of donor-acceptor pair in Znln2 S4 can be significantly tailored by electrostatic gating due to efficient tunability of Fermi level (Ef ). Furthermore, the layer-dependent dipole orientation of defect emission in Znln2 S4 is directly revealed by back focal plane imagining, where it presents obviously in-plane dipole orientation within a dozen-layer thickness of Znln2 S4 . These unique features of defects in Znln2 S4 including extrinsic absorption, rich recombination paths, gate tunability, and in-plane dipole orientation are definitely a benefit to the advanced orientation-functional optoelectronic applications.

Investigating the Probability of the Charging Transition Rate in Cu Contact to P6 System Devices

In this paper, we investigate the probability of the charge transfer interaction process from Cu metal to P6 molecule systems using charge transfer rate calculations. The charge transfer rate from donor Cu metal to an acceptor P6 molecule dye is presented with reorientation energy, electronic drive force, and barrier height emphasis on the effects of transfer processes in the Cu/P6 system. Charge transfer flow probability from Cu metal contacts to P6 dye molecule has recently been considered within the perturbation theory method, where the charge transfer rates have been found to be affected by strength coupling and reorientation energy. The charge transfer could be occurred even at large reorientation energy, less driving force energy, and low potential barrier. It requires to reorientation the donor to acceptor energy levels to start the charge transfer. It has been found that the rate of charge transfer processes enhance the flow rate yield of the transfer cross interface dependent on the potential barrier.

Creating zinc-hyperdoped silicon with modulated conduction type by femtosecond laser irradiation

Silicon, as the earth-abundant semiconductor, has low cost and good compatibility with mature complementary metal-oxide-semiconductor technology. Therefore, instead of choosing the proper semiconductor with a specific bandgap energy, hyperdoping technique, which can introduce deep-level dopants and intermediate band into silicon, enable silicon to operate in infrared wavebands. Particularly, the hyperdoped silicon with transition metals, having low ionized impurity scatting, makes silicon a promising infrared detection material. In present work, zinc-hyperdoped silicon is fabricated by femtosecond pulsed laser irradiation. The doping concentration of zinc has exceeded 1019 cm−3, and even reached 1022 cm−3, which is about five orders of magnitude greater than the solid solubility of zinc in crystalline Si. The zinc-hyperdoped silicon shows sub-bandgap absorptance of 87.86 % at 1310 nm. Temperature-dependent Hall effect measurements prove that zinc doping results in acceptor energy level located at 0.520 eV above the valence band maximum. It is worth nothing that, zinc-oxygen related defect state results in donor energy level located at 0.252 eV below the conduction band minimum when lower laser fluence is used, which means the energy level of impurity is altered by the presence of undesignedly doped oxygen atoms, suggesting compound formation between the zinc atoms and oxygen atoms.

Rhodanine-Based Non-Fullerene Acceptors for Organic Solar Cells with a High Open-Circuit Voltage of 1.07 V

To overcome the intrinsic limitations of fullerene-based organic photovoltaic (OPV) devices, research on OPV devices based on non-fullerene acceptors (NFAs) has been actively conducted in recent years. It is important to understand the relationship between the structure of the NFAs and photovoltaic properties to create high-performance OPV devices. In this study, we have designed and synthesized a series of NFAs (DFDO-RC2 and DFDE-RC2) based on electron-rich dithienosilole (D) and electron-deficient difluorobenzodiathiazole (F), benzodiathiazole-connected 3-ethylrhodanine (RC2) units, and alkyl chains of 2-ethylhexyl (E) and octyl (O) groups. The PTB7-Th:DFD-RC2 devices showed low PCEs mainly due to the highly located highest occupied molecular orbital (HOMO) energy levels of the DFD-RC2 acceptors compared to the PTB7-Th polymer donor. To lower the HOMO levels of the DFD-RC2 NFAs, the backbone structures were modified by replacing difluorobenzodiathiazole core moiety with difluorobenzene (FBz) to obtain DFBz-RC2 molecules (DFBzO-RC2 and DFBzE-RC2). PTB7-Th:DFBz-RC2 devices exhibited significantly improved PCEs compared to PTB7-Th:DFD-RC2 devices. The DFBzO-RC2 and DFBzE-RC2 molecule-based OPVs exhibited remarkably high Vocs of 1.03 and 1.07 V, respectively, which characteristic is associated with the very low energy loss (Eloss) of 0.51 eV in both PTB7-Th:DFBzO-RC2 and PTB7-Th:DFBzE-RC2 devices. Overall, our investigation of the various synthesized molecules reveals the structure-to-photovoltaic properties, which guide the design of new high-performance NFAs to advance in the field of organic solar cells.

Copper oxide stabilized oxy-functionalized boron nitride‑carbon nanotube nanohybrid: An ultra-stable electrode for flexible asymmetric supercapacitor device in ionic electrolyte

This work explores the smart combination of functionalized boron nitride (mK-BN) and carbon nanotube (CNT), stabilized with copper oxide (CuO), as a highly stable, flexible supercapacitor electrode in low-cost viable ionic electrolyte. Oxy-surface modified boron nitride (BN) was introduced to induce supplementary acceptor and donor energy levels for charge transport. Incorporation of CNT facilitated the charge storage through EDLC mechanism and also reduced internal resistance. In three-electrode analysis, CuO/mK-BN/CNT nanohybrid exhibited specific capacitance (Csp) of 425 F/g in aqueous KCl. An asymmetric supercapacitor (ASC) device using CuO/mK-BN/CNT as cathode achieved a Csp of 80 F/g and 36 Wh/kg energy density with ⁓88 % stability after 25,000 charging-discharging cycles in organic electrolyte. To further boost the capacitive performance, energy density, and rate capability of the ASC device, a low-cost, solvent free, and viable ionic electrolyte [(NEt3H)+(HSO4)−] was introduced. In ionic electrolyte, device showed a maximum Csp of 132 F/g with an enhanced energy density of 59.4 W h/kg. ASC devices in ionic electrolyte also exhibited superior volumetric energy density of 1.410 mW h/cm3 and excellent electrochemical performances after connecting two cells in parallel or in series combination implying the capability of the device to produce different required capacitance and potential for practical application. Finally, a flexible ASC device with the ionic electrolyte was also tested. This work established that with the smart combination of additional energy level induced functionalized BN, conducting nanotubes, and pseudocapacitive CuO, a highly stable, flexible asymmetric supercapacitor device can be fabricated with high energy density.

The effect of two intermediate band energy levels in ZnTe solar cell

The intermediate band (IB) effects on the ZnTe(O) solar cells with oxygen defects have been widely investigated. A favorable influence on the conversion efficiency was predicted numerically, provided that oxygen doping concentrations are very high to allow a tunneling effect between IB energy levels for more light absorption. By incorporating more than one intermediate band energy level in a direct band gap materials such as ZnTe material, the effects of the intermediate bands are predicted by numerical simulation to be more pronounced on the performance of the solar cells, we realized a simulation study on an intermediate band solar cell (IBSC) based on ZnTe(O) with oxygen impurities. Indeed, oxygen incorporates multiple acceptor and donor mid-gap levels in ZnTe, we investigated in this study on the influence of two intermediate band (IB) energy levels: the first at 0.53 eV (acceptor energy level) below the conduction band edge and the second at 0.33 eV (donor energy level) above the maximum of the valence band.

High-yield aqueous synthesis of partial-oxidized black phosphorus as layered nanodot photocatalysts for efficient visible-light driven degradation of emerging organic contaminants

The layered nanodot derived from 2D materials is an emerging member of the advanced functional material family. However, its development in applications is still facing inevitable challenges, and one of them is the synthesis strategy with environmental consideration. Herein, we report an aqueous strategy for high-yield fabrication of black phosphorus (BP) layered nanodots. Without using any organic solvent, the initial red phosphorus (RP) fine powder is successfully converted to BP nanostructures at 180–205 °C under the low pressure of 2.7–7.8 MPa and the high yield of 78% is achieved. The synthesized BP nanodots are partial-oxidized, and demonstrate proficient photocatalytic abilities in the visible-light driven degradation of emerging organic contaminants. The photocatalytic mechanism of BP nanodots is dependent on the specific electronic band structure with an acceptor energy level at 0.6 eV above the valence band. The first principle calculation reveals that the surface oxidation layer assists the passivation by hydrogen in aqueous circumstance and establishes the receptor function of BP nanodots. Therefore, our study not only accomplishes a novel route for the environment-friendly fabrication of BP layered nanodot photocatalysts for efficient degradation of emerging organic contaminants, but also contributes to the in-depth understanding of layered nanodots.

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Insights into the Local Bulk-Heterojunction Packing Interactions and Donor–Acceptor Energy Level Offsets in Scalable Photovoltaic Polymers

Isogenous Asymmetric–Symmetric Acceptors Enable Efficient Ternary Organic Solar Cells with Thin and 300 nm Thick Active Layers Simultaneously

AbstractIntegrating desirable light absorption, energy levels, and morphology in one matrix is always the aspiration to construct high‐performance organic solar cells (OSCs). Herein, an asymmetric acceptor Y6‐1O is incorporated into the binary blends of acceptor Y7‐BO and donor PM6 to prepare ternary OSCs. Two isogenous asymmetric–symmetric acceptors with similar chemical skeletons tend to form alloy‐like state in blends due to their good compatibility, which contributes to optimizing the morphology for efficient charge generation and extraction. The complementary absorption of two acceptors helps to improve the photon harvesting of ternary blends, and the higher lowest unoccupied molecular orbital (LUMO) energy level of Y6‐1O offers the chance to uplift the mixed LUMO energy levels of acceptors. Combining the aforesaid benefits, the ternary OSCs with 10 wt% Y6‐1O produce a top‐ranked power conversion efficiency (PCE) of 18.11% with simultaneously elevated short‐circuit current density, open‐circuit voltage, and fill factor in comparison to Y7‐BO‐based binary devices. Furthermore, the optimized ternary OSCs with ≈300 nm active layers obtain a champion PCE of 16.61%, which is the highest value for thick‐film devices reported so far. This work puts forward an avenue for further boosting the performance of OSCs with two isogenous acceptors but different asymmetric structures.

P-type ZnO for photocatalytic water splitting

Global environmental pollution and energy crisis have been regarded as important issues in recent years, making people aware of the need to develop environmentally friendly energy sources. ZnO photocatalysts play a key role in the development of hydrogen generation from water splitting via a photocatalytic strategy. ZnO generally exhibits n-type conductivity, and the difficulty in preparing p-type for forming stable p–n junctions limits its large-scale application. The doping of related elements into ZnO can introduce new shallow acceptor energy levels to achieve p-type conductivity and also overcome the barrier of the wide bandgap to accomplish higher light absorption efficiency. Meanwhile, the realization of p-type ZnO can facilitate the construction of ZnO-based homojunctions and heterojunctions, which will accelerate the photoinduced charge separation and then enhance the photocatalytic water splitting performance. In this Perspective, we discuss recent advances in the fabrication of p-type ZnO by different dopants and describe the benefits of p-type ZnO compared to n-type ZnO for photocatalytic applications. Finally, we analyze the difficulties and challenges of p-type ZnO employed in photocatalytic water splitting and consider the future advancement of p-type ZnO in an emerging area.

Energy levels of acceptor impurities in β-Ga2O3 nanostructures

Applying the methods of the density functional theory and ab initio pseudopotential, the characteristics of the energy levels of acceptors in β-Ga2O3 nanostructures are obtained from the first principles. Mg and Ca are most favorably included in the position of Ga1 and Ga2 in both the cluster and the film. N is most favorably included in the O1 position in the film. The spatial distribution of valence electron density, the density of states, acceptor levels, and band gap width for these nanostructures are calculated.

NO2 gas sensor with excellent performance based on thermally modified nitrogen-hyperdoped silicon

NO2 gas sensing properties of the nitrogen-hyperdoped black silicon (N-Si) modified at different annealing temperatures are studied. Owing to the abundant defects in the material and their changes with the annealing, the thermal modification brings a series of novel sensing behaviors and characteristics. Working as the sensitive material in a conductometric gas sensor, the pristine N-Si exhibits an undesirable n- to p-type response transition for higher NO2 concentration, which severely reduces its upper limit of detection (< 5 ppm). However, for the thermally modified N-Si after annealing at higher temperature (≥ 673 K), the abnormal response transition induced by higher concentration disappears. These modified N-Si show consistent p-type response to all tested NO2 concentrations, successfully breaking the detection limit. More interestingly, there is an optimal annealing temperature ~ 873 K, at which the sensor demonstrates outstanding sensing performances, including wide dynamic range spanning 5 orders of magnitude, rapid adsorption and desorption ability, high response and good selectivity, etc. Results indicate that through the thermal modification a novel N-Si gas-sensitive material is obtained. The mechanism for the thermally-induced response type conversion is discussed, in which the activation of acceptor energy levels provided by the complexes associated with substitutional nitrogen are considered.

Ladder-Type Fused Benzodithiophene Extended along the Short-Axis Direction as a New Donor Building Block for Efficient Organic Solar Cells.

Ladder-type fused aromatic systems are important core structures of small molecule acceptors for organic solar cells (OSCs). In this study, a new ladder-type donor building block, based on the benzo[1,2-b:4,5-b']dithiophene (BDT) unit where the 3,7 positions of the BDT thiophene rings and the 3' position of the thiophene rings of the vertical BDT were fused to construct a seven-ring core structure named f-DTBDT, was investigated. In the f-DTBDT structure, the fusion of the BDT core and the thiophene rings at the 4,8 positions of BDT constrains all of the aromatic rings in a coplanar structure. The newly designed f-DTBDT was successfully employed as a core donor building block and conjugated with three electron-withdrawing acceptors (2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2HIC), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC), and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2ClIC)) as acceptor-donor-acceptor (A-D-A)-type acceptor materials for OSCs. Characterization results showed that the three synthesized A-D-A acceptors of DTBDT-IC, DTBDT-4F, and DTBDT-4Cl have high absorption behavior in the vis-NIR region as result of an intramolecular charge transfer interaction engendered by f-DTBDT and the ending group. The absorption regions of the acceptors were complementary with that of polymer PM6. Also, the frontier orbital energy levels of the new acceptors and wide-band-gap PM6 are well matched. Bulk heterojunction OSCs were fabricated using PM6 and the acceptors, and the highest power conversion efficiency (PCE) of 10.15% was obtained when using PM6:DTBDT-4F as the active layer.