Acceptor Defects Research Articles

Two-step synthesis of antimony sulfide thin films: enhancement in physical properties through sulfurization

Recently, there has been an increase in the use of antimony sulfide (Sb2S3) in Si-based tandem solar cells as a potential absorber material for top sub-cells. The choice of the material stems from the favoured properties such as appropriate bandgap, simple binary composition, nontoxic elements, and long-term stability. However, the physical properties and practical applicability of these materials depend largely on their synthesis conditions. In this work, we investigate the role of sulfurization on the structural, morphological, compositional, and optical properties of Sb2S3 thin films deposited on soda-lime glass via a thermal evaporation technique. Sulfurization was performed on the as-prepared thin films in a customized Chemical Vapor Deposition (CVD) chamber at five different temperatures. Analysis of the crystallinity of the film using the x-ray diffraction technique illustrates the transformation of the film from impure, poor crystalline phase to phase-pure, and highly crystalline orthorhombic structure due to sulfurization. Scanning electron microscopic investigations of the samples revealed better grains with nanorods on the surface at a temperature of 400 °C. For the samples investigated here, the energy values estimated via density functional theory (DFT) calculations agreed well with the experimental data obtained from UV-visible absorption spectral studies. Additionally, it was observed that the desired near-stoichiometric Sb2S3 thin films could be achieved via sulfurization, and the presence of Sb2S3 in all samples was confirmed via Raman spectroscopic studies. Additionally, the defects and trap states of the prepared films were investigated using photoluminescence studies, and donor and acceptor defects were identified. Our study revealed that sulfur rich Sb2S3 films prepared at a sulfurization temperature of 400 °C produced the desired structure, morphology, and optical qualities for future photovoltaic applications.

Analysis of CdS/CdTe Thin Film Solar Cells as a Function of CdS Doping Concentration: A Numerical Simulation Perspective

Cadmium Telluride (CdTe) photovoltaics, incorporating a thin film of Cadmium Sulfide (CdS), present a costeffective yet less efficient solar cell technology. Improving CdS/CdTe solar cell efficiency involves optimizing parameters like doping concentration and CdS layer thickness. However, limited research on cell defects necessitates a comprehensive analysis, including the often-overlooked impact of temperature. This study aims to analyze defect-free and defective CdS/CdTe solar cells, exploring the effects of doping concentration and other parameters. Using the SCAPS-1D simulator, design parameter variations will be investigated, and key metrics— open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and efficiency (η)—will be extracted. Simulation results indicate minimal efficiency impact from increased doping concentration in the ntype CdS layer for defect-free devices. The optimal doping concentration for CdS is 5 × 10<sup>18</sup> cm<sup>-3</sup>, with an optimum electron affinity of 4.0 eV. CdS thickness shows no significant efficiency impact, with the chosen optimum at 10 nm. In the defect-free CdS/CdTe solar cell, key metrics were Voc: 1.06 V, Jsc: 24.60 mA cm<sup>-2<sup>, FF: 87.89%, and η: 23.01%. Analysis of defects revealed single acceptor defects significantly impacting solar cell performance in both interfacial and bulk defects. Defect structure simulations demonstrated that increasing doping concentration, decreasing electron affinity, and thickness enhance efficiency. New optimum values for these parameters—1 × 10<sup>18</sup> cm<sup>-3</sup>, 4.0 eV, and 10 nm—yielded Voc: 1.03 V, Jsc: 23.88 mA cm<sup>-2</sup>, FF: 87.15%, and η: 21.40%. Additionally, a temperature decrease was associated with increased efficiency.

Intrinsic point defects investigation in InAlAs with extrapolated defect transition level

The intrinsic point defects in InAlAs have been studied by first-principles calculations, with a simplified approach to rescale the charge transition levels from the semilocal to the hybrid functional level. Both antisite defects and vacancy defects exhibit a high sensitivity to growth conditions. For Al-poor, In-poor and As-poor growth conditions, AsAl, AsIn and VAs demonstrate the lowest defect formation energy, respectively. All antisite defects including AsIn, AsAl, InAs and AlAs, exhibit donor-like behavior in the band gap as well as VAs. Both VIn and VAl are amphoteric defects, which can behave as donor defects or acceptor defects.

Modeling a tandem solar cell based on Sb2S3 and Sb2Se3 absorber layers

A device simulation presented for a tandem solar cell of Sb2S3 and Sb2Se3 as top (Eg = 1.7 eV) and bottom (Eg = 1.2 eV) absorber layers. We examined the device characteristics, radiative recombination, and optimum thickness of this tandem cell using filtered spectrum analysis and current-matching techniques in COMSOL. An open-circuit voltage of 1.58 V, current density of 15.50 mA/cm−2, fill factor of 56.90 %, and a remarkable efficiency of 14 %. The optimum thickness of Sb2S3 is 350 nm and for Sb2Se3 is 760 nm. Promising characteristics obtained with a Jsc = 16.32 mA/cm2, Voc = 1.48 V, FF = 60.7 %, and an overall power conversion efficiency of 14.66 %. The optimum acceptor and bulk defect density have been calculated to be NA = 8.9 × 1015 cm−3 and BDD = 7.21 × 10−15 cm−3. The optimized values of radiative recombination rate in Sb2S3 and Sb2Se3 are 0.73 × 10−10 cm3/s and 6.5 × 10−11 cm3/s, respectively.

Fabrication of highly conducting undoped ZnO ceramics by flash sintering

Highly conducting undoped ZnO ceramics were fabricated by flash sintering using commercial pure ZnO powder as a model system. The flash-sintered samples with diameters of 15 mm and heights of 2 mm exhibited relative densities ranging from 93.6% to 97.1% and room-temperature electrical conductivities between 205 and 590 S/cm. X-ray diffraction and Raman spectra indicated a high concentration of oxygen vacancies and zinc interstitials in the flash-sintered samples, increasing the carrier concentration. Detailed microstructural analyses show that clean grain boundaries and the morphology and distribution of impurities in flash-sintered samples are favorable for improving carrier mobility. Additionally, flash sintering has the advantage of reducing conditions, which reduces acceptor defects at ZnO grain boundaries, lowers Schottky barriers, and increases carrier mobility. The results show that flash sintering can synergistically enhance the carrier concentration and mobility in ZnO ceramics, making it a promising technique for fabricating highly conducting ZnO ceramics.

Efficiency Improvement of Lead‐Free La2NiMnO6‐Based Double Perovskite Solar Cells Using Numerical Simulation

In this work, the efficiency of lead‐free La2NiMnO6 (LNMO)‐based double perovskite solar cells is optimized using solar cell capacitance simulator (SCAPS‐1D). Herein, the device performance is boosted by using different combinations of electron‐transport layers, hole‐transport layers, absorber layer thickness, acceptor doping density, acceptor defect density, and bandgap tuning, and by modifying the electron affinity. To make the device more realistic, the performance of the proposed device is carefully modified in the presence of interface defect density ≈10−13 cm−3, series resistance ≈1 Ω cm2, and shunt resistance ≈6000 Ω cm2, respectively. From the findings, the optimized device exhibits a record open‐circuit voltage = 1.23 V, short‐circuit current density = 27.18 mA cm−2, fill factor = 87.14%, and power conversion efficiency = 29.20% for FTO/SnO2/LNMO/MoO3/Au configuration. Finally, the device performance is tested under different working temperatures, and 300 K is found as the best temperature for the device.

Defect engineering and alloying strategies for tailoring thermoelectric behavior in GeTe and its alloys

GeTe exhibits excellent p-type medium-temperature thermoelectric properties with low toxicity and good mechanical characteristics, making it highly promising for development in the thermoelectric field. However, GeTe is prone to producing Ge vacancies, leading to high p-type carrier concentration, which results in elevated electronic thermal conductivity and a low Seebeck coefficient. This study systematically analyzes intrinsic and extrinsic defects in GeTe and its alloys, focusing on reducing p-type carrier concentration through first-principles calculations. The results reveal that substituting Ge-sites with Bi (BiGe) yields lower donor defect formation energy, effectively reducing p-type carrier concentration of GeTe and its alloys compared to other elemental doping. Additionally, alloying with certain elements, such as Pb, proves favorable for decreased p-type carrier concentration due to lowered energy levels of valence band maximum (VBM). Inspired by this, screening divalent elements for alloying on Ge-sites reveals that Sr, Ba, Eu, and Yb substantially reduce the VBM of GeTe. Further calculations for Ba and Yb-alloyed GeTe confirm changes in formation energies for donor (favorable) and acceptor (unfavorable) defects. Our work provides a systematic investigation of intrinsic and various extrinsic doping defects in GeTe and its alloys, shedding light on possible strategies of optimizing carrier concentration in these compounds.

Electronic Properties of F, Cl and H Atoms Adsorbed on CsPbI3(110) Surface

The electronic properties of the CsPbI3 surface are calculated by using first-principles calculations. Through calculating adsorption energy of CsPbI3 passivated by Cl, F and H atoms, it is found that adsorption energy values of CsPbI3 (110) surface passivated by H atoms fluctuate less, they are less sensitive to the adsorption position, and the adsorption is stable. Through calculating surface states of passivation system, it is found that F and H atoms have quite good passivation effect, and the Fermi level of passivation system increases and enters the forbidden band, indicating that the passivation effect is relatively ideal. Passivation effect of Cl atoms are poor, a new shallow acceptor defect states appeared at the bottom of the conduction band. This defect level could trap carriers and weaken the carrier migration ability, which is a disadvantage of Cl passivation system. Through the charge density difference and Bader charges, it is found that the F and H atoms get more electrons from the I atom, which is beneficial to the passivation of the surface states.

Optimisation and numerical analysis of highly efficient CGSe-based thin film solar cell

Among the various chalcopyrites compounds used in photovoltaic devices, Copper Gallium Selenium (CGSe) turns out as an underperformer due to its limited photovoltaic performance, So far highest efficiency measured is about 11.9%. This paper investigates the possibilities for efficiency enhancement for the CuGSe layer in Cu2O/CGSe/TiO2/ZnO thin film solar cell structure using the SCAPS-1D simulation program. The short circuit current (Jsc) and power conversion efficiency (PCE) is 30.77 mA cm−2 and 27.10%, with open-circuit voltage (Voc) and fill factor (FF) of 1.03 V and 84.72% respectively. Furthermore, we evaluated some specific parameters of TiO2/CGSe heterostructure, such as the influence of layer thickness, operating temperature, the effect of defect density and acceptor density of CGSe layer, metal work function, and the effect of series and shunt resistance on cell performance. We investigated that combining TiO2 as an ETL and Cu2O as HTL with a CGSe absorber layer is novel and promising, which results in higher power conversation efficiency and improves other PV parameters. The application of CGSe/TiO2 heterojunction in a simulated model offers a viable method for the development of high-efficiency solar cell devices.

SIMULATION STUDIES OF CR DOPED CUO HETEROJUNCTION SOLAR CELL

1% and 3% Cr doped CuO thin films have been deposited on soda lime glass by spin coating method and then their structural, morphological and optical properties have been investigated by operating X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Ultraviolet-Visible Spectroscopy (UV-Vis) techniques, respectively. XRD patterns of CuO:Cr (1%) and CuO:Cr (3%) thin films demonstrate characteristics of monoclinic CuO structure with a C2/c space group. The morphology of coated film plays an important role in analyzing some optoelectronic properties. 1% Cr doped CuO thin film absorbs more photons compared to 3% Cr doped CuO in Vis and UV regions. The band gaps of 1% Cr and 3% Cr doped CuO thin films are to be 2.18 eV and 2.30 eV, respectively. The Mo/1% and 3% Cr doped CuO/n-ZnO/i-ZnO/AZO solar cell has modelled with SCAPS-1D simulation program. The photovoltaic (PV) parameters of solar cell deteriorated with some increase in the neutral defect density (N_t) value. As the shallow acceptor defect density (N_a) value is increased, J_SC is decreased, V_OC, FF and η are increased. PV performance of 1% Cr doped CuO solar cell were found to be better than that of 3% Cr doped CuO solar cell. The efficiency of 1% Cr doped CuO solar cell is increased with the use of SnO2 intermediate layer in 2 nm thickness at the heterojunction interface.

Impact of Grain Size and Grain Nature in Thin‐Film Solar Cells

Herein, a theoretical investigation is conducted on grain‐size inhomogeneity's impact and grain boundaries’ (GBs’) electrical nature in thin‐film solar cells. Using the Matthiessen rule, grain‐size‐dependent mobility is derived in polycrystalline material. The obtained grain‐size‐dependent mobility values are fed into the Poisson solver to calculate device performance. The severity of grain sizes in the lower region determines how grain size affects the photovoltaic performance by grain‐size‐dependent efficiency simulation. Low grain sizes become critical, especially for low‐thickness absorbers. The second aspect of the study assesses potential variation at GBs to reveal the impact of the electrical properties of GBs. Evidence shows that the acceptor defects at GB are benign for device performance, causing upward band bending at the GB and acting as electron barriers. Device performance is adversely affected by donor defects at GBs due to downward band bending. As summarized in the findings, the polycrystallinity‐induced cause–effect relationships of grains are likely to interest solar cell researchers.

Superior Electromechanical Compatibility in Lead-Free Piezoceramics with Mobile Transition-Metal Defects.

Donor and acceptor ions serving as extrinsic defects in piezoelectrics are mostly used to improve the performance merits to satisfy the industrial application. However, the conventional doping strategy is unable to overcome the inherent trade-off between the piezoelectric coefficient (d33) and mechanical quality factor (Qm). Herein, inspired by the valence state variation observed in manganese oxides during sintering, this study focuses on manipulating intrinsic oxygen vacancies and extrinsic manganese defects in potassium sodium niobate (KNN) ceramics via heat treatment. The annealing process results in a simultaneous improvement in both d33 (20%) and Qm (80%), leading to comparable performance with commercial PZT-5A ceramics and enabling their application in atomizer components. Moreover, the mechanism of manganese occupation and diffusion is proposed by an extended X-ray absorption fine structure and density functional theory analysis. The improved electromechanical performance in the annealed KNN ceramic is associated with the optimized redistribution of acceptor and donor manganese defects, which is facilitated by the recombination of oxygen vacancies. This work breaks longstanding obstacles in comprehending the existing forms of manganese in KNN and offers potential in popularizing KNN-based piezoceramics to replace traditional PZT lead-based counterparts in the industrial market.

On the possibility of p-type doping in barium stannate

The combination of optical transparency and bipolar dopability in a single material would revolutionize modern opto-electronics. Of the materials known to be both p- and n-type dopable (such as SnO and CuInO2), none can satisfy the requirements for both p- and n-type transparent conducting applications. In the present work, perovskite BaSnO3 is investigated as a candidate material: its n-type properties are well characterized, with La-doping yielding degenerate conductivity and record electron mobility, while it has been suggested on a handful of occasions to be p-type dopable. Herein, group 1 metals Li, Na, and K and group 13 metals Al, Ga, and In are assessed as p-type acceptor defects in BaSnO3 using a hybrid density functional theory. It is found that while K and In can induce hole concentrations up to 1016 cm−3, the low energy oxygen vacancy pins the Fermi level in the bandgap and ultimately prevents metallic p-type conductivity being achieved in BaSnO3. Nevertheless, the predicted hole concentrations exceed experimentally reported values for K-doped BaSnO3, suggesting that the performance of a transparent p–n homo-junction made from this material could be significantly improved.

Native defects association enabled room-temperature p-type conductivity in β-Ga2O3

The room temperature hole conductivity of the ultra-wide bandgap semiconductor β-Ga2O3 is a pre-requisite for developing the next-generation electronic and optoelectronic devices based on this oxide. In this work, high-quality p-type β-Ga2O3 thin films grown on r-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD) exhibit ρ = 5 × 104 Ω·cm resistivity at room temperature. A low activation energy of conductivity as Ea2 = 170 ± 2 meV was determined, associated to the VO++−VGa−native acceptor defect complex. Further, taking advantage of cation (Zn) doping, the conductivity of Ga2O3:Zn film was remarkably increased by three orders of magnitude, showing a long-time stable room-temperature hole conductivity with the conductivity activation energy of around 86 meV. VO++−ZnGa− defect complex has been proposed as a corresponding shallow acceptor.

Thermal degradation and defect growth in CZTSSe photovoltaic devices

Thermal degradation of Kesterite thin film solar cells (CdS/CZTSSe) has been studied using three different time-dependent models which formulate the defect growth kinetics within the depletion width of CZTSSe/CdS junction. Generation and annihilation of a shallow acceptor defect at 0.55 eV under the stress of heating at 400 °C for 1000 h have been modeled. Three cases were modeled for defect growth rate by relating defect generation to electrons and hole density increment linearly (n) or quadratically (np or n2). The non-radiative recombination has been modeled for the three models and enabled the calculation of heat generation across the depletion width. The heat generation was also mapped through a coupled optical-electrical-thermal model in COMSOL for defect growth models at elevated stressing time. Heat generation is then stronger for the n-model and rises to double times higher by increasing the stressing time to 1000 h.

Optimization and Performance Analysis of a TiO2/i-CH3NH3SnBr3/CsPbI3/Al(BSF) Heterojunction Perovskite Solar Cell for Enhanced Efficiency.

This paper reports the simulation and optimization of heterojunction perovskite solar cells (PSCs) with a proposed structure of TiO2/i-CH3NH3SnBr3/CsPbI3/Al(BSF) using SCAPS-1D software. The purpose of this study is to investigate the performance of the PSC with CsPbI3 perovskite active layers and i-CH3NH3SnBr3 as the permeable layer. Therefore, the thicknesses of the layers of the heterojunction perovskite are modified in order to find a better conversion efficiency of the solar cell, where the latter's performance is improved by optimizing the absorber's thickness, which is found to be 1 μm, with a permeable layer of 15 μm. The device efficiency of the i-CH3NH3SnBr3/CsPbI3 heterojunction is improved to 38.98%, and optimized parameters are Voc = 1.21 mV, Jsc = 35.63 mA/cm2, and FF = 89.84%. The acceptor concentration (Na), donor concentration (Nd), defect density, and series and shunt resistances are also investigated.

Microscale Engineering of n-Type Doping in Nanostructured Gallium Antimonide: AC Impedance Spectroscopy Insights on Grain Boundary Characterization and Strategies for Controlled Dopant Distribution.

This paper investigates the microscale engineering aspects of n-type doped GaSb to address the challenges associated with achieving high electrical conductivity and precise dopant distribution in this semiconductor material. AC impedance spectroscopy is employed as a reliable technique to characterize the microstructural and electrical properties of GaSb, providing valuable insights into the impact of grain boundaries on overall electrical performance. The uneven distribution of dopants, caused by diffusion, and the incomplete activation of introduced dopants pose significant obstacles in achieving consistent material properties. To overcome these challenges, a careful selection of alloying elements, such as bismuth, is explored to suppress the formation of native acceptor defects and modulate band structures, thereby influencing the doping and compensator formation processes. Additionally, the paper examines the effect of microwave annealing as a potential solution for enhancing dopant activation, minimizing diffusion, and reducing precipitate formation. Microwave annealing shows promise due to its rapid heating and shorter processing times, making it a viable alternative to traditional annealing methods. The study underscores the need for a stable grain boundary passivation strategy to achieve significant improvements in GaSb material performance. Simple grain size reduction strategies alone do not result in better thermoelectric performance, for example, and increasing the grain boundary area per unit volume exacerbates the issue of free carrier compensation. These findings highlight the complexity of achieving optimal doping in GaSb materials and the importance of innovative analytical techniques and controlled doping processes. The comprehensive exploration of n-type doped GaSb presented in this research provides valuable insights for future advancements in the synthesis and optimization of high-conductivity nanostructured n-type GaSb, with potential applications in thermoelectric devices and other electronic systems.

Effect of the Diffusion of Copper Atoms in Polycrystalline CdTe Films Doped with Pb Atoms

The process of diffusion of labeled copper atoms in p-CdTe<Pb> coarse-block films with a columnar grain structure has been studied. The CdTe<Pb> film is a p-type semiconductor, where an increase in the Pb concentration in the composition of the CdTe films increases the resistivity ρ of the structure. When the Pb concentration in CdTe changes from 1018 to 5·1019 cm-3, the hole concentration decreases by more than 3 orders of magnitude at a constant operating level depth of EV + (0.4 ± 0.02) eV. This may indicate that the concentration of acceptor defects, which are formed in the films due to self-compensation upon doping with a PbCd donor, exceeds the number of the latter. Electrical measurements by the Hall method were carried out at a direct current and a temperature of 300 K. As a result, an increase in the temperature of films on a Mo-p-CdTe<Pb> substrate during annealing affects the electrical parameter of charge carrier mobility µ, it decreases significantly. X-ray diffraction analysis showed that on the diffraction patterns of samples of p-CdTe<Pb> films, all available reflections correspond to the CdTe phase and up to х = 0.08 do not contain reflections of impurity phases and have a cubic modification. Based on the results of the calculation, it was established that the low values of the diffusion coefficient of Cu atoms are due to the formation of associates of the A type , which are directly dependent on the concentration of atoms. Diffusion length Ln and lifetime τn of minority current carriers in large-block p-type cadmium telluride films, which can also be controlled by introducing lead atoms into cadmium telluride.

Device modelling and optimization of various n-i-p configurations for MASnI3 perovskite solar cells to achieve high efficiency using Solar Cell Capacitance Simulator-1D

Perovskite materials are potential light harvesters, and in specific tin-based absorbers such as methyl ammonium tin iodide (MASnI3) are non-toxic with distinguished optoelectronic properties. This is the first simulation report to explore the application of strontium titanate (SrTiO3) as an electron transport layer (ETL) in planar n-i-p MASnI3 perovskite solar cell (PSC) device. In an attempt to enhance the output performance of MASnI3 PSCs, a systematic approach is devised to determine appropriate alternative charge-selective materials via solar cell capacitance simulator (SCAPS-1D) software. The significance of varying thickness, donor doping concentration, acceptor doping concentration, defect density, diffusion length, and energy band offset for the reference PSC configuration TiO2/MASnI3/Spiro-OMeTAD are investigated. The optimized reference structure delivered 19.72% efficiency. In pursuit of high photovoltaic performance, seven different electron transport materials were comparatively examined. As a result, PCBM, In2S3, and CeO2 were considered not suitable due to their limited electrical performance. Consequently, seven inorganic hole transport layers (HTL) along with four suitable ETL were utilized in MASnI3 PSC to construct twenty-eight novel n-i-p device structures whose efficiency ranges between 14.20% and 22.77% respectively. The influence of varying the work function of back contact, series resistance, shunt resistance, and temperature on the photovoltaic parameters was analysed. The vital parameters investigated in this simulation for implementing state-of-the-art PCS are energy band offset, diffusion length, activation energy, recombination current profile, and built-in-potential. The device configuration featured with SrTiO3/MASnI3/CuO and SrTiO3/MASnI3/MASnBr3 achieved a maximum efficiency of 22.77% and 22.60%, respectively. The PSC tailored with SrTiO3 have better thermal stability and enhanced fill factor, which accounts for improving the output power. These novel findings of all-inorganic PSC will provide preliminary support for practical implementation.

How Halide Alloying Influences the Optoelectronic Quality in Tin-Halide Perovskite Solar Absorbers.

Halide alloying in tin-based perovskites allows for photostable bandgap tuning between 1.3 and 2.2 eV. Here, we elucidate how the band edge energetics and associated defect activity impact the optoelectronic properties of this class of materials. We find that by increasing the bromide:iodide ratio, a simultaneous destabilization of acceptor defects (tin vacancies and iodine interstitials) and stabilization of donor defects (iodine vacancies and tin interstitials) occurs, with strong changes arising for Br contents exceeding 50%. This translates into a decreased doping which is, however, accompanied by a higher density of nonradiative recombination channels. Films with high Br content show a high degree of disorder and trap state densities, with the best optoelectronic quality being found for Br contents of around 33%. These observations match the open circuit voltage trend of tin-based mixed halide perovskite solar cells, supporting the relevance of optoelectronic properties and chemistry of defects to optimize wide-bandgap tin perovskite devices.