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Although perovskite solar cells (PSCs) have captured notable interest as a potential candidate for third-generation solar cells, due to their favorable optoelectronic properties, cost-effectiveness, and high efficiency, some issues related to device stability and toxicity of the perovskite (PSK) layer hinders the commercial viability of PSCs. The inherent instability of organic PSK halides and the toxicity of Pb has compelled researchers to focus on developing Pb-free all-inorganic PSCs by replacing the organic species with inorganic (Cs+) cations as a safer alternative. In this study, the SCAPS-1D simulator was employed to investigate the cell performances of all-inorganic Pb-free Cs-based PSCs with three different PSK layers (CsGeI3, CsSnI3, and Cs2TiI6) individually, where inorganic ZnO and CuSCN were used as the electron transport layer (ETL) and the hole transport layer (HTL), respectively. The Cs2TiI6-based PSC was found to have the best performance. Then, the defect tolerance level of the PSK layer and the impact of band offset on cell performances were investigated. The optimum values of the conduction band offset (CBO) and the valence band offset (VBO) were found to be 0 eV and between − 0.1 eV and 0 eV, respectively. Moreover, the effect of interface defects at the ETL/PSK and PSK/HTL interfaces on cell performance was also analyzed as a function of CBO and VBO and, for both cases, the interface defect tolerance limit was recorded as 1016 cm−2. This study observed a high rate of recombination for negative values of CBO and VBO at the interfaces. Thus, these findings will guide researchers in developing high-performance PSCs with suitable inorganic Pb-free perovskite and charge transport layers. [ABSTRACT FROM AUTHOR]

Diamond is a material with promising electronics applications but with challenges in effective doping. Cubic boron nitride (cBN), due to its similar lattice structure, is ideal for forming heterostructures with diamond, to modify electronic properties and especially shift the band positions. Here it is demonstrated how integrating cBN layers of finite thickness in diamond can induce an electronic band offset near the polarized diamond‐cBN interface. Beyond the direct density functional theory computations, an analytical model is developed for rapid examination of the band offset, for a broad number of crystallographic orientations, in excellent agreement with ab initio calculations. Results show that near [100] and [111] crystal directions, the diamond|cBN|diamond heterostructure displays a 3–4 eV band offset which is expected to facilitate effective modulation doping of diamond. [ABSTRACT FROM AUTHOR]

In this research, we examined metallic back contacts effects on the electrical characteristics of heterojunctions in the context of solar cells. Gold, silver, aluminum and copper were selected as substitutes for the conventional molybdenum. Heterojunctions with SnS and ZnS as an absorber and buffer layers, respectively, were fabricated using spray pyrolysis. The characterization revealed the formation of SnS in an orthorhombic structure and ZnS in a cubic structure, displaying preferential orientations along (120) and (222) planes, respectively. These structures exhibited excellent crystallinity, evidenced by large crystallite sizes and phase purity, as confirmed by morphological study. Optical measurements indicated the band gap for SnS and ZnS as 1.5 and 3.1eV, respectively. Additionally, through Hall Effect and Mott–Schottky analysis, it was observed that the SnS and ZnS films displayed p-type and n-type conductivity, with corresponding carrier concentrations of 1.87×1018 and 1.41×1019cm−3, respectively. The electrical characteristics of the n-ZnS/p-SnS heterojunction were explored through forward I–V analysis. Photocurrent measurements revealed that the constructed structures demonstrated rectifying behavior. The resistance series and ideality factor values obtained were observed to be relatively high. The unusual ideality factor can be attributed to the formation of Schottky contact between contacts (Ag, Al, Cu) and SnS film, possibly due to defects at the interface state of ZnS/SnS. This study’s findings indicate that, among the tested FTO/ZnS/SnS heterojunction structures, with Au metal contact exhibited superior performance. It suggests that Au could serve as a viable alternative to Mo as the back metal contact for SnS-based solar cells. [ABSTRACT FROM AUTHOR]

Abstract The h-BN/diamond mix-dimensional heterostructure has broad application prospects in the fields of optoelectronic devices and power electronic devices. In this paper, the electronic properties and band offsets of hexagonal boron nitride (h-BN)/(H, O, F, OH)-diamond (111) heterostructures were studied by first-principles calculations under biaxial strain. The results show that different terminals could significantly affect the interface binding energy and charge transfer of h-BN/diamond heterostructure. All heterostructures exhibited semiconductor properties. The h-BN/(H, F)-diamond systems were indirect bandgap, while h-BN/(O, OH)-diamond systems were direct bandgap. In addition, the four systems all formed type-II heterostructures, among which h-BN/H-diamond had the largest band offset, indicating that the system was more conducive to the separation of electrons and holes. Under biaxial strain the bandgap values of the h-BN/H-diamond system decreased, and the band type occurred direct–indirect transition. The bandgap of h-BN/(O, F, OH)-diamond system increased linearly in whole range, and the band type only transformed under large strain. On the other hand, biaxial strain could significantly change the band offset of h-BN/diamond heterostructure and promote the application of this heterostructure in different fields. Our work provides theoretical guidance for the regulation of the electrical properties of h-BN/diamond heterostructures by biaxial strain.

The h-BN/diamond mix-dimensional heterostructure has broad application prospects in the fields of optoelectronic devices and power electronic devices. In this paper, the electronic properties and band offsets of hexagonal boron nitride (h-BN)/(H, O, F, OH)-diamond (111) heterostructures were studied by first-principles calculations under biaxial strain. The results show that different terminals could significantly affect the interface binding energy and charge transfer of h-BN/diamond heterostructure. All heterostructures exhibited semiconductor properties. The h-BN/(H, F)-diamond systems were indirect bandgap, while h-BN/(O, OH)-diamond systems were direct bandgap. In addition, the four systems all formed type-II heterostructures, among which h-BN/H-diamond had the largest band offset, indicating that the system was more conducive to the separation of electrons and holes. Under biaxial strain the bandgap values of the h-BN/H-diamond system decreased, and the band type occurred direct–indirect transition. The bandgap of h-BN/(O, F, OH)-diamond system increased linearly in whole range, and the band type only transformed under large strain. On the other hand, biaxial strain could significantly change the band offset of h-BN/diamond heterostructure and promote the application of this heterostructure in different fields. Our work provides theoretical guidance for the regulation of the electrical properties of h-BN/diamond heterostructures by biaxial strain. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of a ZnGeN2 layer inserted into the wells of Type-I InGaN/GaN QWs LEDs on the electrical and optical properties by using the Silvaco TCAD Simulator. First, the new structure is compared to the standard type-I LED based on InGaN. We found that using ZnGeN2 layer in the In0.2Ga0.8N-QWs LED leads to wavelength extending from the blue to the red region. Next, we highlighted the effect of quantum well number and In-molar fraction in the wells of InxGa1-xN/ZnGeN2 type-II LEDs. As a result, increasing the number of wells from two to six QWs creates an extension of spontaneous emissions while keeping a low concentration of indium in the wells (x = 0.16) and improving the electrical and optical properties, as we found an improvement in light output power of 10.7% at 40Acm-2. [ABSTRACT FROM AUTHOR]

Based upon the 10-band kp approach, the electronic properties, namely the electronic band structure, effective mass, band offset, their ratio, and optical gain of AlGaAsN/GaAs, have been studied. An extensive range of electronic bandgaps spanning from 0.866 eV and 0.942 eV are observed. Considering strain, 16.7 meV/N% (keep 2%Al) splitting rates were observed due to the compressive strain. While under tensile strain, we observed a changeover from type II to type I heterostructure with a valence band offset ratio (Qv) of 0.21 < 1, which is the definition for type I heterostructure. However, a conduction band offset ratio (Qc) of 0.795, a higher value, is advantageous as it establishes better electron confinement. It is shown that (x = 0.05, y = 0.04) is the more suitable couple of contents for developing Al x Ga 1 - x As 1 - y N y / GaAs single quantum well compounds are emitting in the telecommunications windows range. Increasing nitrogen concentration and an active region's dimension leads to a red shift in the gain spectra. While under the influence of compressive and tensile strain, lateral variation by 214 nm is observed in the optical gain spectra. We also studied the variation of threshold current density with a density of injected carriers. These findings may help future optical device applications. [ABSTRACT FROM AUTHOR]

This article comprehensively investigates the photovoltaic performance of a 3% GeI2‐doped ASnI2Br absorber in a solar cell. The cell features an inverted structure (fluorine‐doped tin oxide [FTO]/poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate [PEDOT:PSS]/absorber/C60/Ag) and utilizes EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98 as the A‐site cation (EDA for ethylenediamine; GA for guanidinium; FA for formamidinium). Through systematic numerical simulation and optimization, the photovoltaic performance of the solar cell is enhanced by sequentially optimizing several parameters: 1) absorber thickness and defect density, 2) conduction band offset at the ASnI2Br/C60 interface, doping of the electron‐transport layer (ETL), and its interface with the absorber, and 3) valence band offset at the PEDOT:PSS/ASnI2Br interface, and doping of the hole‐transport layer and its interface with the absorber. Additionally, the impact of series resistance (Rs) variation on device performance is investigated. Starting with an initial power conversion efficiency (PCE) of 4.86%, the systematic numerical optimization process elevates it to an impressive 18.55%. Furthermore, a final cell structure is proposed where C60 is replaced with indium‐doped tin oxide (ITO) as the ETL layer. This optimized FTO/PEDOT:PSS/absorber/ITO structure demonstrates a remarkable PCE of 18.68%. These findings hold significant promise for advancing tin‐perovskite solar cell technology. [ABSTRACT FROM AUTHOR]

Tandem solar cells have the potential to surpass conventional single-junction photovoltaics by harnessing a wider range of the solar spectrum and reducing losses caused by thermalization and transmission. This study examines the performance of a kesterite-kesterite tandem solar cell with two different absorber layers in each subcell using SCAPS-1D. The upper subcell comprises CZTS and ACZTS with wider bandgaps, while the lower subcell comprises ACZTSe and CZTSe with narrower bandgaps. The CZTS- and CZTSe-based solar cells were first validated using experimental data to determine the feasibility of the tandem solar cell design. The CZTS-based solar cell was modified by replacing the back contact, adding a Cd-free buffer layer of ZnMnO, and using a SnMnO2 layer as a window layer. The band gap and electron affinity of ZnMnO and SnMnO2 layers were adjusted by changing their manganese contents for optimal conduction band offset. A thin ACZTS layer was also added as a second absorber layer in the CZTS-based solar cell to enhance open circuit voltage. The CZTSe-based solar cell was thereafter modified by including an ACZTSe layer as a second absorber layer and by selecting ZnSe as a buffer layer and optimizing the thicknesses of all layers. Both upper and lower subcells were analyzed for tandem configuration using filtered spectra and current-matching techniques. The thickness of the CZTS layer in the upper subcell was adjusted to achieve current matching; consequently, the proposed tandem cell had an efficiency of ∼24%. These findings provide valuable insights for future advancements in kesterite-kesterite-based tandem solar cells.

In this paper, we report the comparative study of some parameters of II–VI ternary alloy ZnCdTe and II–VI–O dilute oxide ZnCdTeO. The purpose of this comparative study is to establish both the ternary and quaternary alloys as superior materials for optoelectronic and solar cell applications in which the quaternary materials show more superiority than the ternary material. In this purpose, we take the data from the experiments previously done and published in renowned journals and books. The parameters of these alloys are mainly being calculated using Vegard's law and interpolation method of those collected data. It was certainly demonstrated that the incorporation of O atoms produces a high bandgap (Δ E g ) reduction in host ZnCdTe (Zn 1 − x CdxTe) in comparison to the bandgap reduction in host ZnTe material with Cd incorporation. The bandgap of ZnCdTeO (Zn 1 − x CdxTe 1 − y Oy) was found to be reduced to 1.1357 at x = y = 0. 5 and the spin–orbit splitting energy ( Δ SO ) value of ZnCdTeO was calculated to be 1.175 eV for Cd concentration of 0.5 mole and O concentration of 0.1 mole both of which showed excellent results with the prospect of optoelectronic and solar cell applications. The constant rise in the spin–orbit curve signifies a very less internal carrier recombination which decreases the leakage current and augments the efficiency of solar cell. The lattice constants and strain calculation values give very good results and confirm the stability of the materials. Besides, the calculated band offsets values show that for ZnCdTeO, there is higher bandgap reduction than that of ZnCdTe. Moreover, ZnCdTeO covers a wide range of wavelength in the visible region starting from violet region at 393 nm upto red region at 601 nm. Both ZnCdTe and ZnCdTeO are found to have excellent applications in optoelectronic and solar cell devices though quaternary ZnCdTeO proves much supremacy over ternary ZnCdTe in all aspects of the properties. [ABSTRACT FROM AUTHOR]

In this study, the theoretical modelling of perovskite solar cells (PSCs) aimed at achieving high performance is explored using the SCAPS-1D simulator. Various materials, including TiO2, PCBM, ZnO, SnO2, Zn(O,S), Spiro-MeOTAD, PEDOT:PSS, NiO, CuO, Cu2O, CuSCN, and CuSbS2, with a wide range of band offset values were studied as charge transport layers (CTLs) for PSCs. The impact of band offset at the CTL/absorber interface on the performance of PSCs was examined. The objective is to identify charge transport layers that facilitate stable device operation using abundant and cost-effective materials that can be prepared through simple methods. Additionally, a systematic variation of device parameters is performed to optimize the efficiency of the PSCs. The influence of different metal contacts, including Ag, Cu, Fe, C, and Au, on solar cell performance is also examined. Among the investigated CTLs, the highest power conversion efficiency (PCE) of 30.20% is achieved with the HTL PEDOT:PSS, followed by approximately 28% PCE with Spiro-MeOTAD, CuSCN, and Cu2O. PSCs utilizing electron transport layers (ETLs) of TiO2, PCBM, SnO2, Zn(O,S), and ZnO, along with HTL Spiro-MeOTAD, demonstrate comparable device performance, with a PCE of around 28%. By combining these optimized HTLs and ETLs, 35 different PSC configurations are obtained, out of which 25 exhibit a PCE greater than 26%. PSCs with HTLs of NiO and CuSbS2 display a smaller drop in PCE at higher operating temperatures compared to other PSCs, suggesting their superior temperature stability. Several materials have been investigated as hole transport layer (HTL) and electron transport layer (ETL) for perovskite solar cells (PSCs). HTLs with low valence band offset (VBO) values have exhibited impressive PCE exceeding 26%. However, HTLs with high VBO values (−0.3 eV and −0.38 eV) have led to a degradation in the performance of PSCs (PCEs < 23%). To address cost concerns, the expensive gold (Au) anode can be substituted with a more affordable carbon electrode, offering a promising alternative. [ABSTRACT FROM AUTHOR]

Recently, van der Waals heterojunctions (vdWHs) constructed from two two-dimensional materials have attracted considerable attention. In particular, vdWHs based on black phosphorus (BP) have shown excellent photoelectric properties. In this work, we construct a BP/GeTe vdWH and investigate its electronic and optical properties. We find that the BP/GeTe vdWH has a type-II band alignment. Its optical absorption exhibits a red shift compared to the freestanding BP and GeTe monolayers. The electric field and strain effects on the BP/GeTe vdWH are also investigated. The band offsets can be modulated by the electric field and the strain. The BP/GeTe vdWH will convert from type-II to type-I when applying an electric field and to type-III under strain, which will expand the application of BP/GeTe vdWHs in transistor devices. Furthermore, the strain can significantly enhance the optical absorption and induce the red shift of the absorption edge, which indicates the broad applications of the BP/GeTe vdWH in photodetector devices. [ABSTRACT FROM AUTHOR]

The design and configuration of solar cells are critical for photovoltaic action and achieving high efficiency. Herein, the double‐absorber solar‐cell architecture of low‐bandgap Sb2Se3 and high‐bandgap Cu2ZnSnS4 (CZTS) absorbers for broader spectrum utilization leading to higher efficiency are comprehensively analyzed. The cost‐effective chalcogenides CZTS and Sb2Se3 for high‐efficiency dual‐absorber configuration to show the possibility of high wattage at a lower cost are taken. The crucial parameters of bandgap pair and thickness are optimized for synergetic device performance and optimal utilization of the incident spectrum. By introducing an additional absorber–absorber interface, the interfacial defect at CZTS/Sb2Se3 is lowered by optimizing the band offset for the efficient functioning of a double–absorber device. The proposed device has straightforward NiO/CZTS/Sb2Se3/AZO architecture suitable for low‐cost fabrication with high efficiency of 30.9%. [ABSTRACT FROM AUTHOR]

Photoinduced charge transfer (CT) is decisive to the efficiency and speed of photoelectric conversion in two-dimensional (2D) van der Waals (vdWs) heterostructures. Generally, CT rate enhancement is realized by increasing the band offset (BO). In this study, we propose that a fast and efficient CT can be realized via strong hybridization of energy levels in 2D vdWs heterostructures with minimal BO. First-principles calculations reveal that the smallest energy difference between conduction-band edges and minimal BO in the WS2/WxMo1−xS2 (x = 0.78) heterostructure yields the strong hybridization of energy levels and then results in ultrafast CT (2.7 ps). Experimental results agree with theoretical calculations. The photoluminescence of WS2 is quenched in the WS2/WxMo1−xS2 (x = 0.78) heterostructure, attributable to the strong hybridization-induced fast and efficient CT. This study provides insights into the mechanism of CT in heterostructures and offers new strategies to create superior optoelectronic devices with fast and efficient photoelectric conversion. [ABSTRACT FROM AUTHOR]

The numerical simulations of optical and electronic properties of BGaAsBi/GaAs quantum wells (QWs) are obtained by diagonalizing the 16-band kp Hamiltonian with distinct boron and bismuth compositions that exhibit multifaceted potential in 1.3–1.5 μm. It has been observed that under strain-relaxed conditions for a doping concentration of 12.5 % (B, Bi), the anticipated values of spin-orbit (SO) coupling energy (Δ SO) and the bandgap (E g) are 302 meV and 0.952 eV, respectively. Additionally, strain interaction on band structure decreases the band gap from (E g = 0.92eV–0.85eV), increasing dopant concentration from 8 % to 12.5 %. The consequence of incorporating both Bi and B impurity is a reduction in electron effective mass of BGaAsBi by ∼1.3 times concerning the host GaAs, enhancing the optical properties of BGaAsBi/GaAs quantum-confined heterostructures. Moreover, an increase in well-width introduced a red shift and reduced the peak amplitude of the gain spectra. In addition, for solar cell application, the onset of the fundamental absorption edge is depicted at an energy of about 0.96 eV. For laser applications, the optimum threshold current density and quality factor of BGaAsBi/GaAs quantum well achieved at room temperature are 1089 A/cm2 and 3653, respectively, at well width (w = 2.0 nm), cavity length (L = 0.5 mm), and average thickness of the active region (d = 45 nm). The variation in power density is studied with injected current density, while the quality factor is calculated with well width. The outcomes could be beneficial for future use in optical devices. • Band structure of BGaAsBi/GaAs studied using 16 band kp model. • Observing an extensive range of electronic bandgaps and corresponding operating wavelengths spanning from 0.92 eV (∼1.34 μm) to 0.85 eV (∼1.5 μm) is observed for B and Bi impurity concentrations up to 8 % and 12.5 %, respectively. • Incorporation of 12.5 % (B, Bi) into the host GaAs leads to a decrease in electron effective mass by 1.3 times. • The onset of the fundamental absorption edge is depicted at an energy of about 0.96 eV. • Increasing well width leads to a red shift in the gain spectra and a reduction in peak amplitude. • Variation of threshold current density is studied with temperature, cavity length, the average thickness of region, and well-width conditions. (The lowest threshold current density value at 77 K is 142 A/cm2, but at 300 K is 1089 A/cm2.) • The power density variation was studied with injected current density and the quality factor variation with well width. [ABSTRACT FROM AUTHOR]

The introduction of heterojunction structures in perovskite solar cells (PSCs) can lead to substantial enhancements in power conversion efficiency (PCE) and stability. Using the SCAPS-1D software, we have theoretically investigated the performance potential of CsPbI 3 /Cs 2 SnI 6 heterojunction PSCs. The purpose of incorporating a thin layer of Cs 2 SnI 6 perovskite onto the CsPbI 3 layer is to enhance the stability of the device through the formation of a protective barrier that prevents the continuous degradation of CsPbI 3. The device's overall efficiency was found to be greatly enhanced by meticulously optimizing the acceptor concentration (N A), defect density (N t), and absorber thickness of CsPbI 3. In addition, the influence of various physical parameters such as the operating temperature, the work function of the metal rear contact, and series and shunt resistance on the photovoltaic performance of the device is comprehensively examined. With the systematic optimization of these parameters, the device exhibited improved performance and attained an outstanding PCE of 20.86 %, an open circuit voltage (V OC) of 1.19 V, a fill factor (FF) of 81.77%, and a current density voltage (J SC) of 21.32 mA/cm2. We think that our work will provide theoretical guidance in the advancement of heterojunction devices with much improved efficiency and stability. • The introduction of a bilayer absorption resulted in an increase in the photovoltaic performance of the device. • Carrier separation and transport are facilitated by the ideal band structure of solar cells. • Strong correlation between the solar cell's performance and the defect density, doping concentration, and electron affinity. • The optimized device exhibited an impressive PCE of 20.86 %. [ABSTRACT FROM AUTHOR]

Herein monoclinic selenium thin films are used as substrates to grow hexagonal cadmium bromide thin films. It is found that selenium substrates enhance the growth of larger crystallites and reduces the microstrain and defect density in CdBr2. The conduction and valance band offsets of the Se/CdBr2 interfaces are found to be 1.25 eV and 0.54 eV, respectively. With these band offset values the light absorbability of CdBr2 in the visible range of light are remarkably increased. In addition, interfacing of Se with CdBr2 significantly increased the real part of dielectric constant and forced dielectric resonance in the infrared and visible ranges of light. Moreover, the optical conductivity parameters including the drift mobility, the scattering time at femtosecond level and the plasmon frequency for Se/CdBr2 is optimized using Drude-Lorentz approach. It found that coating CdBr2 onto Se result in enhancement of the drift mobility and plasmon frequency values allowing them reaching ~ 44 cm2/Vs and 0.77 GHz and 22 cm2/Vs and 5.69 GHz, when exposed to infrared and ultraviolet radiation, respectively. It is also observed that Se/CdBr2 optical receivers can perform as terahertz band filters showing constant cutoff frequency values of 3.0 THz and 15.0 THz in the infrared and visible ranges of light, respectively. [ABSTRACT FROM AUTHOR]

Abstract Semiconductor photovoltaics have been investigated for many years, and various materials and device architectures have been developed aiming for low cost and high efficiency. Despite the critical advances in the field, there are confusions in understanding such diode based solar cells, especially on open‐circuit voltage and fill factor. This review intends to provide a succinct summary and interpretation for the core elements that are related to a solar cell device. First, the fundamental concepts of PN junction and diode solar cell are introduced. Second, Fermi and quasi‐Fermi levels are described, followed by understanding open‐circuit voltage and fill factor. Thirdly, the effects of heterojunction band offset are discussed. In the end, a brief conclusion is presented.

Perovskite Solar Cells (PSCs) are the most promising candidates for low-cost and high-efficiency devices in the future photovoltaic market. PSCs are also used as the top cell in tandem devices with silicon bottom cells. However, research in PSCs is still at an early stage while racing towards a promising future. Along with experimental research, numerous simulation studies are conducted with PSCs aiming to analyze new materials and optimize their performance. Here, a wavelength-dependent model is implemented to account for the reflected part of irradiance from the cells, which is ignored in most SCAPS-1D based PSC simulated models. This model optimizes the MgF2 anti-reflective coating in SCAPS-1D simulation to allow maximum photons to pass inside the device. A simple structured PSC (MgF2/Glass/ITO/ZnO/CH3NH3PbI3/Spiro-OMeTAD/Au) is simulated and optimized optically as well as electrically with this model’s modified spectrum. The device was optimized for layer thickness, defects, and doping. Moreover, the effects of temperature and device resistances are discussed. The optimized device yields 21.62% power conversion efficiency, which can be further improved to reach over 25% through better processing schemes. Finally, the optimized device was compared with other devices having different ETL/absorber/HTL combinations and the pathway to achieving higher efficiencies was discussed. This article aims at improving the credibility of simulated devices by incorporating top surface reflection with electrical optimization.

The thermal stability and material properties of HfO2 thin films on Si substrates with and without H2O2 wet chemical oxidation were investigated. The HfO2 samples were deposited through plasma‐enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H2O2 wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO2 deposition. After the annealing process at 600°C, the band gap (Eg) of the HfO2 films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO2. Furthermore, the conduction and valence band offsets (ΔEc and ΔEv, respectively) between HfO2 and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H2O2 wet oxidation of the Si substrate, a 1.5‐nm chemical oxide was formed instead of a native oxide. The band offset and Eg values of HfO2 were similar before and after 600°C annealing (ΔEv = 3.86 eV, ΔEc = 1.02 eV, and Eg = 6.0 eV), implying the high thermal stability of the HfO2 films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO2 gate oxides in Si‐based integrated circuit devices. [ABSTRACT FROM AUTHOR]

In photovoltaic sector, optimal utilization of the solar spectrum combined with improved power conversion efficiency is the call of the day. Such elasticity is provided by heterostructure solar cells. But it is found that with a high lattice mismatch and band discontinuities, the open‐circuit voltage (Voc) and the fill factor deteriorates handsomely. As a result, the second requirement is still unsatisfied. To address such issues, band alignment engineering is introduced in this paper. Silvaco ATLAS is used to virtually create and verify the proposed model. Herein, different recombination events and their effects on the cell's Voc are investigated in depth. Furthermore, interface trap defect is introduced to investigate its effect on the lower efficiency and Voc. However, it is found that, in GaAs/GaSb heterostructures, the reduced Voc and efficiency issues can be avoided, because the proposed model is able to achieve a lower trap density of 105 cm−2. [ABSTRACT FROM AUTHOR]

[Display omitted] • To develop four van der Waal heterojunctions, we vertically stacked hexagonal Boron Nitride (h-BN) and four Transition metal dichalcogenides (TMDCs), namely h-BN/WS2, h-BN/WSe 2, h-BN/MoS 2 and h-BN/MoSe2, using a wet transfer technique. • X-ray photoelectron spectroscopy (XPS) measurements were used to determine the Valence Band Offset (VBO) values of the heterojunctions. • It is important to note that each heterojunction was a type I heterojunction. • The study illustrate the impact of chalcogen on VBO values in heterojunctions and found that VBO values increase when chalcogen transitions from S to Se in TMDCs. In order to analyze the effect of the chalcogen on the band alignment of the Transition metal dichalcogenides (TMDCs) and hexagonal Boron Nitride (h-BN) heterojunction, we fabricated the h-BN/TMDCs heterojunction by vertically stacking mono-layer h-BN and multi-layer TMDCs by the wet transfer method. The four heterojunctions are h-BN/WS 2 , h-BN/WSe 2 , h-BN/MoS 2 and h-BN/MoSe 2. X-ray photoelectron spectroscopy (XPS) has been employed to ascertain the Valence Band Offset (VBO) at the junctions created among these heterojunctions. All heterojunction band alignment styles are type-I. When the chalcogen changes from S to Se, the heterojunction VBO values increase. Specifically, in case of h-BN/WS 2 and h-BN/WSe 2 the VBO is 2.42 eV and 2.81 eV, respectively, and the magnitude of the difference is 0.39 eV. In the same case for h-BN/MoS 2 and h-BN/MoSe 2 the VBO is 2.52 eV and 2.55 eV, respectively, and the magnitude of the difference is 0.03 eV. The aforementioned research has obtained the band alignment for four heterojunctions, which provides a valuable reference for the design and analysis of the correlation devices in the future. [ABSTRACT FROM AUTHOR]

A direct bandgap type-I Ge QDs/Ge1−y−zSnySiz double-heterostructure on Ge1−xSnx virtual substrates is proposed for SWIR and MWIR lasers. The Ge1−y−zSnySiz barrier is lattice-matched to Ge1−xSnx. The band structures are calculated with different to Sn contents in Ge1−y−zSnySiz and Ge1−xSnx. The band edge energies of Ge QDs vary linearly with x, and independent with y. The Γ-valley is below L-valley when x exceeds 7.5%. The ground states of electrons of Γ- and L-conduction band varies with both x and y. High x and y can increase the conduction band offsets and decrease the valence band offsets. Emission wavelengths range from 1.91 to 4.6 μm are achieved from the proposed structure with proper Sn contents. Emission wavelength of direct bandgap type-I Ge QDs/Ge1-y-zSnySiz on Ge1-xSnx VS. [ABSTRACT FROM AUTHOR]

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MgO and SiO2 are the natural oxide layer on the surface of Mg2Si and the excellent gate dielectric layer materials. MgO/Mg2Si and SiO2/Mg2Si heterojunctions were successfully prepared by magnetron sputtering. The valence band offset (VBO) and conduction band offset (CBO) of the two heterojunctions were measured by X‐ray photoelectron spectroscopy (XPS) method, and the values were 2.64 and 3.90 eV for MgO/Mg2Si and 3.24 and 4.43 eV for SiO2/Mg2Si, respectively. Different degree of band bending occurs on the two interfaces. As a result, the band diagrams of the both interfaces are all Type‐I (Straddled) band alignment. Such high VBO and CBO can provide suitable barrier heights for both electrons and holes (>1 eV); therefore, both MgO and SiO2 can be suitable candidates for the preparation of Mg2Si‐based thin film transistors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The performance of eco-friendly lead-free CsBi 3 I 10 -based perovskite solar cell has been numerically analyzed. • Enhancement of open circuit voltage (V OC) up to 360 mV has been observed after introduction of NiO x HTL. • The influence of key defect parameters of the CsBi 3 I 10 absorber and CeO x /CsBi 3 I 10 interface layer have been extensively studied. • Exploration of energy band alignment impact on the device performance. Bismuth-based halide perovskite (CsBi 3 I 10) is a promising absorber material for the fabrication of eco-friendly perovskite solar cells (PSCs). In this research, the performance of the CsBi 3 I 10 -based PSCs with different hole transport layers (HTLs) has been numerically analyzed. The open circuit voltage (V OC) has enhanced up to 360 mV after the addition of NiO x HTL in the heterostructure of the CsBi 3 I 10 -based PSC. A comprehensive numerical study of the role of band alignment, key defect parameters of the CsBi 3 I 10 absorber layer, and CeO x /CsBi 3 I 10 interface on the newly designed heterostructure (ITO/CeO x /CsBi 3 I 10 /NiO x /Au) performance of the CsBi 3 I 10 -based PSC has been conducted. A massive deterioration of the V OC has been initiated when defect concentration (N t) of CsBi 3 I 10 crosses above 1014 cm−3. Apart from the N t , defect energy level within the bandgap (E t), and holes capture cross-section (σ p) of the CsBi 3 I 10 layer have also significantly affected the V OC loss. Besides, the investigation indicates that the device performance is almost independent of E t of the CeO x /CsBi 3 I 10 interface and slightly decreases with the increase of N t and σ p. Finally, the photovoltaic performance of the PSC has been explored for various thickness and carrier concentration of the CsBi 3 I 10 , cerium oxide (CeO x), and nickel oxide (NiO x). Therefore, this research provides efficient guidelines for the fabrication of eco-friendly high-performance CsBi 3 I 10 -based PSCs. [ABSTRACT FROM AUTHOR]

• Novel buffer layer 3C-SiC used in CIGS thin-film solar cell. • Highest efficiency of 25.51% is achieved at ΔE c = 0.91 eV or E g (CIGS) = 1.45 eV for 50 nm thin 3C-SiC buffer layer. • Existence of interface recombination centers yielded activation energy of 1.417 eV. • Proposed structure shows good thermal stability, as J sc increases by 0.04%/K and V oc decreases on an average by 1.77 mV/K. Cubic Silicon Carbide (3C-SiC) can be a potential photovoltaic material for thin-film solar cells because of its wide bandgap and non-toxic nature. In this work, we present 3C-SiC as an alternative to the conventional CdS buffer layer and investigate the performance of the proposed 3C-SiC/CIGS cell structure using solar simulator SCAPS-1D. The simulation starts with the optimization of 3C-SiC buffer layer thickness followed by the study of conduction band offsets (CBO) impact on the photovoltaic performance parameters. The highest obtained efficiency is 25.51% (V oc = 0.94 V, J sc = 31.46 mA/cm2) at CBO, ΔE c = 0.91 eV with the optimized buffer thickness. The linear extrapolation study of V oc as a function of temperature yields the activation energy which tells the existence of interface recombination centres. Next, the inclusion of the acceptor defect state at the 3C-SiC/CIGS interface determines the maximum acceptable defect density of the proposed cell structure. Afterward, the thermal stability through temperature study is performed and compared to the traditional CdS/CIGS structure. The results provided here give few paramount indications that lead to a highly efficient CIGS solar cell with a 3C-SiC buffer layer. [ABSTRACT FROM AUTHOR]

In this study, CeO2/TiO2 nanocomposites (NCs) were synthesized by adopting a straightforward two steps method comprising, first, the synthesis of CeO2 and TiO2 nanoparticles by wet chemical precipitation method and second, the heterostructure CeO2/TiO2 NCs by solid-state reaction process. The CeO2/TiO2 NCs were characterized by X-ray diffraction, N2 adsorption–desorption isotherm analysis, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. Regardless of CeO2 content, the bandgap energies of CeO2/ TiO2 NCs were lower than that of pure TiO2. Photocatalytic activity of the synthesized photocatalysts was assessed by degrading a model dye methylene blue under the illumination of UV light. The CeO2/TiO2 NCs containing 2 wt% CeO2 exhibited higher photocatalytic degradation efficiency compared to reference TiO2 (P25), pure TiO2, and CeO2/TiO2 NCs containing CeO2 other than 2 wt%. The alkaline environment was favorable for photocatalytic decomposition of cationic dye methylene blue (MB). The enhanced degradation efficiency of CeO2/TiO2 NCs was substantiated in terms of vectorial charge separation and the reduction of photogenerated charge carriers owing to the band offsets existing at the interface between CeO2 and TiO2 NPs. Finally, no significant change in the degradation efficiency of CeO2/TiO2 NCs after successive uses evidenced the stability and reusability of the photocatalysts. Therefore, it can be concluded that the synthesized CeO2/TiO2 heterostructure photocatalyst would be a promising candidate for application in wastewater treatment. [ABSTRACT FROM AUTHOR]

The absolute volume deformation potential (AVDP) is an important physical quantity that describes the absolute energy level shift of semiconductors under pressure. The valence band maximum (VBM) and conduction band minimum (CBM) AVDPs of inorganic cubic ABX3 perovskites (where A = K, Rb, Cs; B = Ge, Sn, Pb; X = Cl, Br, I) are systematically investigated using ab‐initio simulations. Spin‐orbit coupling (SOC) is found to have negligible effect on the AVDPs of ABX3 perovskites, though it plays an important role in their band structures. The AVDPs of VBM are determined to be all negative and large, meaning the energy level will shift downward as the crystal volumes increase, while AVDPs of CBM are mostly positive and small. The AVDPs of VBM and CBM both increase as the atomic number of X‐site element increases, while the absolute value of VBM's AVDP increases initially and decreases afterward as atomic number of B‐site element becomes larger. These trends can be well explained based on the atomic orbital levels, the hybridization of the band edge orbitals, bond length, and bandwidth. These results provide critical parameters for the band structure engineering design of optoelectronic devices based on the ABX3 halide perovskites through strain control. [ABSTRACT FROM AUTHOR]

Using first principles calculations, this work investigates the suitability of diamond/c-BN heterojunctions for high frequency, high power device applications. The key quantities of band offsets and interface charge polarization are examined for different crystallographic orientations [(110), (111), or (100)], bond terminations (C B or C N), and substrates (diamond or c-BN). The results indicate that both the (111) and (100) structures with polar interfaces are likely to be a type-I alignment with the diamond conduction and valence band extrema nested within the c-BN bandgap, whereas the non-polar (110) counterpart may form type II as the valence band of c-BN is shifted down substantially lower. The valence band offsets are estimated to be around 0.2–0.55 eV and 1.2–1.3 eV for types I and II, respectively, with only a modest dependence on the order of layer stacking and bond termination. The (111) and (100) structures also show net charge polarization in a narrow region at the interface. The electron-deficient and electron-rich nature of the C B and C N bonding are found to induce charge redistribution leading to an essentially 2D sheet of negative and positive polarization, respectively, with a density on the order of 10 12 − 10 13 q / cm 2 (q = 1.6 × 10 − 19 C). With the predicted band alignments suitable for carrier confinement as well as the possibility of the modulation and polarization doping, the diamond/c-BN heterostructures are a promising candidate for high-performance electronic devices with a highly conductive 2D channel. Both p-type and n-type devices appear possible with a judicious choice of the heterojunction configuration. [Display omitted] • Diamond and cubic boron nitride heterostructures are studied for use in devices. • Two of three structures form high charge densities at the interface. • These structures are also candidates for both p-type and n-type devices. • High frequency, high-power devices can likely be made with these structures. [ABSTRACT FROM AUTHOR]

• The band positions of the semiconductor crystals in nanoscale experience a significant shift when they are joined together. • The introduction of Au nanoparticles into the heterojunction interface instigates an additional band offset. • Compared to Si/ZnO array, Si/Au/ZnO array decreases resistance from 85 to 52 Ω and improves photocurrent from 0.5 to 4.0 µA for the superior band alignment. • The reaction rate of Si/Au/ZnO array is nearly twice that of Si/ZnO array and 2.53 times that of Si array. • The change of band position and band alignment by the interfacial regulation can be applied to other semiconductor heterostructures. The exotic performances of semiconductor heterostructures are generally ascribed to the band alignment and band bending at the heterojunction interface for the built-in potential. Herein, theoretic computations and experiments reveal for the first time that the band positions of Si and ZnO experience a significant shift when they are joined together. The introduction of Au nanoparticles into this interfacial layer matrix instigates an additional band offset, leading to the change from type-I to type-II band alignment. Compared to the binary architecture, the superior band alignment of the ternary architecture augments light absorption, concurrently suppressing photoluminescence and reducing resistance from 85 to 52 Ω. Moreover, a substantial improvement in photocurrent is achieved, increasing from 0.5 to 4.0 µA, alongside a significant elevation in photocatalytic activity from 1.90 × 10−3 to 3.67 × 10−3 min−1, indicating potential of the Si/Au/ZnO heterostructure as a promising candidate in optoelectronics and photocatalysis. The current work highlights the band offset and interfacial regulation of the semiconductor heterostructures, which diverges from the band bending for the built-in potential and can be extended to design heterogeneous semiconductor nanomaterials with suitable band alignment for their potential applications. Band offset and interfacial regulation of the core-shell Si/Au/ZnO nanowire array lead to the enhanced photoelectrochemical and photocatalytic performances. [Display omitted] [ABSTRACT FROM AUTHOR]

Using first-principles approach, we calculated the band gaps of wurtzite $ {\rm Be}_{1-x} $ Cd $ _x{\rm O} $ ternary alloy and the band offset of the lattice matched $ {\rm ZnO}/{\rm Be}_{0.44}{\rm Cd}_{0.56}{\rm O}[1\,1\,\overline {2}\,0] $ heterojunction, where the modified Becke–Johnson semi-local exchange was used to determine the band gap and the coherent potential approximation was applied to deal with doping effect in disordered alloys. The $ {\rm ZnO}/{\rm Be}_{0.44}{\rm Cd}_{0.56}{\rm O} $ heterojunction was determined to have a type II band alignment, with valence and conduction band offset being 0.28 and 0.50 eV, respectively. The calculation approach and procedure demonstrated here can be used to predict the band offset of more lattice matched semiconductor heterojunctions.

InSe based heterojunction devices gain importance in optoelectronic applications in NIR range as multipurpose sensors. For this reason, InSe/Sb2Te3 heterojunctions are constructed as NIR sensors by the thermal evaporation technique. The structural, optical, dielectric and photoelectric properties of InSe/Sb2Te3 heterojunctions are explored by X-ray diffraction and ultraviolet-visible light spectrophotometry techniques. The structural analyses revealed the preferred growth of polycrystalline hexagonal Sb2Te3 onto amorphous InSe as a major phase. Optically, the coating of Sb2Te3 onto InSe enhanced the light absorbability of InSe by more than 18 times, redshifts the energy band gap, increased the dielectric constant by ~5 times and increased the optical conductivity by 35 times in the NIR range of light. A conduction and valance band offsets of 0.40 and 0.68 eV are determined for the InSe/Sb2Te3 heterojunction devices. In addition, the Drude-Lorentz fittings of the optical conductivity indicated a remarkable increase in the plasmon frequency values upon depositing of Sb2Te3 onto InSe. The illumination intensity and time dependent photocurrent measurements resulted in an enhancement in the photocurrent values by one order of magnitude. The response time of the devices is sufficiently short to nominate the InSe/Sb2Te3 heterojunction devices as fast responding NIR sensors suitable for optoelectronic applications.

In the present report, the interfacial band offset was investigated in poly (styrenesulfonate) doped poly (3,4-ethylenedioxythiophene) (PEDOT: PSS) and Gallium Nitride (i.e., PEDOT:PSS/GaN) heterojunction using X-ray photoemission studies. A hetero-interface of PEDOT: PSS with molecular beam epitaxy grown GaN surface has been developed, and the changes in morphology and interfacial electronic structure were analyzed. It was observed that the deposition of PEDOT: PSS on GaN pursued uniform coverage and led to a significant reduction in surface roughness from 4.47 to 1.86 nm. Further, the photoemission analysis performed to analysis the band offset in the developed organic/ inorganic hetero-interface revealed a Type-I band alignment with a valence band offset of 1.6 eV. [ABSTRACT FROM AUTHOR]

In this letter, a 400-nm-thick β-Ga2O3 nanomembrane is extracted from an n-Ga2O3-on-silicon wafer by wet etching, and then transferred to a p-GaN/ sapphire wafer by transfer-print technique to fabricate n-Ga2O3/p-GaN heterojunction diodes. X-ray photoelectron spectroscopy (XPS) measurement is used to accurately confirm that the valence-band offset of the heterojunction is 1.41± 0.07 eV. The diodes exhibit excellent electrical properties including high rectification ratio (3.85 × 106 at ±5 V) and low reversed current density (1.51 × 10−7 A ⋅ cm−2 at −5 V). The results show that the lift-off and transfer-print processes pave a new way for fabricating high-performance Ga2O3-based heterojunctions and bipolar devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have been studied extensively in the area of perovskite solar cells because they have a comparatively free hysteresis. Through fabrication of a perovskite solar cell based on a vanadium oxide buffer, this study clarified the mechanism of electron and hole transport in the laminated layer upon irradiation with light. The power conversion efficiency (PCE) of the Vanadium (Ⅳ) oxide (VO 2) sputtering process device was approximately 13% and with the spin-coating process was 8.5%. To investigate the physicochemical origin of such PCE differences depending on the process type, comprehensive band alignment and band structure analyses of the actual cell stacks were performed using X-ray photoelectron spectroscopy depth measurements. Accordingly, it was found that the inconsistent valence band offset between the perovskite absorption layer and V 2 O 5 layer as a function of the VO 2 process type caused a difference in the hole transport, resulting in the difference in the efficiency. Image 1 • The PCE of each device was confirmed to be approximately 5.2% on an average with SC-VOx HTL and 9.6% on an average using the SP-VOx HTL. • The V 2 O 5 layer was naturally formed on top of the VO 2 HTL by air oxidation in both the deposition processes. • The V 2 O 5 , which is a wide band gap material at 2.6 eV, exists between the perovskite absorption layer and VO 2 HTL layer, the band offset at the perovskite/HTL junction is higher for spincoating VO x HTL than that for sputtering VO x HTL by 1.6 eV. • The difference in the surface chemistry depending on the deposition technique gave a rise to a significant variation in the junction bandoffset. [ABSTRACT FROM AUTHOR]

Herein the design of broken gap heterojunction devices made of molybdenum trioxide and zinc phthalocyanine coated onto Al substrates are reported. The devices which are prepared by the thermal evaporation technique under vacuum pressure of 10−5 mbar are observed to exhibit a conduction and valence band offsets of 3.36 and 3.56 eV, respectively. The heterojunction devices are observed to form a subband gap of 0.66 eV between the valence bands edges of ${p-}$ ZnPc and conduction bands edges of ${p}$ -MoO3 leading to a ${p}^{+}{/}{n}^{+}$ heterojunction type. Analysis of the current- voltage characteristics of the devices has shown that it exhibits tunneling diode characteristics with maximum tunneling barriers of width of ~ 45 nm. The device displayed biasing dependent photosensitivity in response to 850 nm laser lights. In addition to its characteristics as MOS device, when it was imposed with ac signals in the frequency domain of 0.01-1.80 GHz, it displayed resonance-antiresonance phenomena accompanied with negative capacitance effect in the studied range of spectra. The analysis of the alternating current (ac) electrical conductivity has shown that the ac conduction is mostly governed by quantum mechanical tunneling assisted with correlated barriers hopping. The laser light photosensitivity, the negative capacitance effect, the capacitance switching within 100 ns and the bandpass characteristics with notch frequency of 1.24 GHz make the Al/MoO3/ZnPc/Al attractive for use as IR sensors, parasitic capacitance cancellers, fast capacitance switches and microwave bandpass filters. [ABSTRACT FROM AUTHOR]

• CsPbBr 3 -based PSCs with a structure of FTO/ETM/CsPbBr 3 /HTM/Au are investigated. • Influences of the band offset and interface defect density, are studied. • Three grading cases of χ are investigated, and a PCE of 11.58% with V OC of 1.68 V is achieved. • Used ZnOS replaced TiO 2 , high V OC of 1.57 V is obtained. • Introduced the bilayer absorption scenario of CsPbIBr 2 /CsPbBr 3 , a PCE of 15.89% is obtained. Recently, inorganic perovskite solar cells (PSCs) based on CsPbBr 3 have triggered incredible interest due to the demonstrated excellent stability against thermal and high humidity environmental conditions. However, the power conversion efficiency (PCE) of the CsPbBr 3 -based PSCs is still lower than that of the organic-inorganic hybrid one, because of the large band gap and serious charge recombination at the interface or inside the device. Here, the working mechanism of the devices with normal n-i-p planar structure is modeled and investigated using SCAPS 1D simulation software. The simulation results state that the proper band structure of PSCs is crucial to carrier separation and transport. The high interface recombination, originated from the large band offsets of the electron transport material (ETM)/absorber and absorber/hole transport material (HTM) respectively, can be effectively diminished with the continuous gradient junction design of the absorber, and a PCE of 11.58% is obtained with a high open-circuit voltage (V OC) of 1.68 V. Moreover, by building a heterojunction bilayer absorption scenario of CsPbIBr 2 /CsPbBr 3 and employing ZnOS and Cu 2 ZnSnS 4 films as the ETM and HTM respectively, the PCE of PSCs is further increased to 15.89%, caused mainly by the enhancement in short-current density (J SC). Moreover, reducing the interface defect density is also very important to improve the performance of PSCs. These results will provide theoretical guidance for improving the performance of the CsPbBr 3 -based PSCs. [ABSTRACT FROM AUTHOR]

• This work emphasizes on modelling of TMDC material, WS 2 , as a potential window layer material for CIGS solar cell. So far none has reported on proposed new CIGS/WS 2 structure. • This research identifies the impact of interface defect state on the photovoltaic parameters of CIGS/WS 2 solar cell and evaluates the tolerance of defect by numerical simulation. • This research paves the way for WS 2 thin film as a potential window layer material for CIGS solar cells. Device modelling of copper indium gallium selenide (CIGS) solar cell with tungsten di-suphide (WS 2) as a window layer has been carried out in order to achieve higher conversion efficiency. Conversion efficiency for all band-gap energies of CIGS were calculated based on proposed new CIGS/WS 2 structure. Numerical modelling tools were used to investigate the effects conduction band offset and interface defect state on the photovoltaic parameters of CIGS/WS 2 solar cell. The model predicts the density of defect tolerance in the interface is 1 × 1011 cm3. Based on optimization, the highest efficiency of 26.4% has been achieved for CIGS/WS 2 solar cell with Eg (CIGS) = 1.4 eV (V oc = 1.026 V, J sc = 29.57 mA/cm2 and FF = 86.96%) which is better than that of CIGS (23.4%) solar cell. The simulation further identifies that proposed CIGS/WS 2 structure is less temperature sensitive compared to conventional Si solar cell. This research paves the way for WS 2 thin film as a potential window layer material for CIGS solar cells. [ABSTRACT FROM AUTHOR]

ZnO/GaN heterostructures are promising systems for solar cells,light-emitting diodes and photocatalytic applications due to their appropriate band gaps that correspond to the wavelength range of visible light and thus have attracted wide attention over the past ten years.In this study, investigations of structural and electronic properties of bulk ZnO, GaN and ZnO/GaN superlattice have been performed based on first-principles calculations within the density functional theory. For a more accurate description of the electronic properties of bulk semiconductor crystals,Hubbard correction to generalized gradient approximation(GGA+U)was applied. The obtained results show that this calculation method allows to obtain reliable band edge positions, which are the defining parameters in determining the average electrostatic potential of each bulk material.Also, the use of the GGA+U method allows obtaining the lattice mismatch of bulk ZnO and GaN within no more than 0.5% compared with experimental results, which confirms once again the reliability of this method.It should be noted not only good accuracy of the obtained results but also low computational and time costs when using the GGA+U method. For calculations of structural and electronic properties of ZnO/GaN heterostructure,the same method as for bulk crystals was used. Based on the obtained band diagram of heterojunction, the band offsets of ZnO/GaN heterostructure were determined. We have verified that these band offsets are in very good agreement with previous experimental and theoretical results. Thus, we obtained a highly efficient method for calculating the band offsets of ZnO/GaN heterostructure that produces fine accuracy at a rational computational expense. [ABSTRACT FROM AUTHOR]

Limits on the conversion efficiency and open-circuit voltage lead to low kesterite thin-film solar cell performance. The conduction band offset (CBO) between the absorber and buffer layers (p-CZTS and n-CdS) is considered to be one of the effective factors for the performance of these devices. The simulation results demonstrated that the optimal thickness and doping concentration for obtaining a high performance in the solar cell which is based on CZTS/CdS absorber/buffer layers would respectively be 50 nm and 1.5 × 1017 cm−3. The CBO at absorber/buffer interface plays a significant role in solar cell performance and the highest CZTS-based solar cell efficiency is obtained within the range of − 0.4 eV and + 0.4 eV of the CBO. Solar cell performance decreases from 5.12 to about 3% when the positive CBO increases from 0.4 to 0.7 eV. Moreover, the impact of CBO on device quantum efficiency was investigated. The optical response range changed with an increase in + ΔEC and the highest value (about 80%) was observed in visible and near ultraviolet light within the range of 400–520 nm. In − ΔEC, electrons can be transferred from the buffer layer to the window layer and the optical photons proportional to the buffer layer's band gap help generate free electrons and holes, which cause a slower reduction of the quantum efficiency within the negative offsets and the above-mentioned range, through electric field bending. In addition, a large number of n-type materials such as CdS, SnS2, ZnO, ZnTe, ZnS, Zn(O, S), (Mg, Zn)O, In2S3, TiO2, and CdTe were analyzed as buffer layers in CZTS-based thin-film solar cell. The CZTS-based thin-film solar cells with SnS2, ZnO0.55S0.45, ZnO0.80S0.20, and Mg0.2Zn0.8O led to a conversion efficiency of about 13%. Furthermore, an open-circuit voltage of above 700 mV was obtained by using ZnO0.40S0.60 and Mg0.1Zn0.9O buffer layers. By introducing the CZTSe/CZTS absorber layer and SnS2 buffer layer in the structure of the proposed solar cell, the best efficiency and open-circuit voltage is deduced as 16.28% and 780 mV, respectively. [ABSTRACT FROM AUTHOR]

High-efficiency laser diodes often adopt high mirror loss design to improve the external differential efficiency of the device. However, the significantly elevated threshold carrier density and exacerbated carrier thermal escape restrict the additional advancements in device performance. By replacing the 7 nm I n A l G a A s quantum well with an 11 nm G a A s P quantum well, there has been a considerable improvement in the differential gain. Furthermore, the higher conduction band offset has effectively inhibits the carrier thermal escape, which significantly improves the internal differential efficiency and temperature stability of the device. The stripe width of device was 150 μ m , and the cavity length was 2 mm. The device was tested under continuous wave current condition with the heat-sink temperature setting to 25 °C. The power conversion effectively is as high as 71% at 5.4 A. The slope efficiency and the threshold current were 1.47 W/A and 0.62 A. • Improvement of power conversion effectively of the laser diode at 780 nm is main target. • G a A s P material is used as a quantum well instead of I n A l G a A s quantum well. • The internal differential efficiency, absorption loss, threshold, and characteristic temperature have been greatly enhanced. • The power conversion efficiency of laser diode is significantly improved. [ABSTRACT FROM AUTHOR]

Terahertz radiation pulses emitted after exciting semiconductor heterostructures by femtosecond optical pulses were used to determine the electron energy band offsets between different constituent materials. It has been shown that when the photon energy is sufficient enough to excite electrons in the narrower bandgap layer with an energy greater than the conduction band offset, the terahertz pulse changes its polarity. Theoretical analysis performed both analytically and by numerical Monte Carlo simulation has shown that the polarity inversion is caused by the electrons that are excited in the narrow bandgap layer with energies sufficient to surmount the band offset with the wide bandgap substrate. This effect is used to evaluate the energy band offsets in GaInAs/InP and GaInAsBi/InP heterostructures.