Work Function Of Electrode Research Articles

Work-function-tunable metal-oxide mesh electrode and novel soluble bipolar host for high-performance solution-processed flexible TADF-OLED

Substantial effort has been dedicated to the development of solution-processed flexible organic light-emitting diodes (sf-OLEDs). However, to simultaneously enhance device performance and ensure stable operation under severe mechanical deformation, highly flexible transparent electrodes and efficient soluble organic emitting materials must be optimized together. Here, highly efficient green-emitting thermally activated delayed fluorescence (TADF) sf-OLEDs were developed using a mesh-structured Ni-doped indium zinc oxide (mNIZO) flexible electrode and a novel soluble bipolar host. The mNIZO electrode had excellent optical, electrical, and mechanical properties. The work function of the mNIZO electrode was engineered through surface doping with Ni without optical and electrical losses. 5-(9 H-Carbazol-9-yl)− 3′-(3,6-di-tert-butyl-9 H-carbazol-9-yl)-[1,1′-biphenyl]− 3-carbonitrile (CzCN-tCz) was synthesized as a soluble host material by incorporating a tert-butyl group into 3,3′-di(carbazol-9-yl)− 5-cyano-1,1′-biphenyl (mCBP-CN). Consequently, the mNIZO-based TADF sf-OLED with CzCN-tCz had a maximum external quantum efficiency of 21.0 % on a poly(ethylene 2,6-naphthalate) substrate, and 82 % of the initial luminance was maintained under severe mechanical stress, which is attributable to the high deformability of the mNIZO electrode. The proposed framework is expected to facilitate the design of high-performance cost-effective flexible displays with various forms through a simple process.

Theoretical analysis of all-inorganic solar cells based on numerical simulation of CsGeI3/CsPbI3 with p-p+ built-in electric field

With the development of perovskite solar cells (PSCs) technology, inorganic perovskite led by CsPbI3 gradually shows the photovoltaic performance of organic perovskite cells. However, this is still based on the organic charge transport layer. CsPbI3 with all-inorganic structure still need to be further studied. Therefore, in this study, an all inorganic CsGeI3/CsPbI3 laminated structure with CsGeI3 instead of organic HTL is introduced, and numerical simulation is carried out through SCAPS-1D (Solar Cells Capability Simulator). It is found that the two perovskite layers, which are both p-type materials, have shown excellent efficiency in the p-p+ built-in electric field. In this paper, PSCs are optimized with absorbing layer thickness, doping concentration, defect density, metal electrode work function and so on. The best thickness is determined according to the different light absorption properties of Pb2+ and Ge2+, and the toxicity of the original single-layer lead based perovskite is reduced. Through the comprehensive analysis of band bending, built-in electric field and recombination rate, we explained the reason why the parameters increase with the growth of doping concentration (NA). In terms of NA regulation, it is found through simulation that when NA of the two absorption layers is at 1015 to 1018 cm−3, the photogenerated carriers are driven by the strong p-p+ built-in electric field to migrate well in the flat energy band, which significantly improves the photovoltaic performance of PSCs. For the defect density the charge transport layer, the PSC absorption characteristics, and the metal electrodes, we made a choice based on the photovoltaic performance and process level. Finally, the power conversion efficiency of the optimized PSCs reached 24.06 % and the fill factor is 86.19 %. This study proved that p-p+ structure constructed by lead germanium mixed metal has great potential for inorganic perovskite solar cells with Cs as a cation in the future.

Pronounced thickness effect of permanent charge-introduced branched poly(ethylene imine) surface-modifying layers in polymer:nonfullerene solar cells

Modification of electrode surfaces in polymer:nonfullerene solar cells have attracted keen interest because it greatly affects the device performance. In this study, we tried to modify the indium-tin oxide (ITO) electrode surface by introducing a branched poly(ethylene imine) (bPEI) nanolayer, which is doped with 3-hydroxypropane-1-sulfonic acid (HPSA), and investigated the thickness effect of HPSA-doped branched PEI layers on the performance of inverted-type polymer:nonfullerene solar cells. The doping ratio of HPSA to bPEI was set to 20 mol% to secure sufficient room for dipole formation, while the bPEI:HPSA thickness was varied between 0 and 5.5 nm. Results showed that the open circuit voltage of devices was remarkably increased by coating the 1.0–3.1 nm-thick bPEI:HPSA layers on the ITO electrodes. The efficiency of solar cells was strongly dependent on the bPEI:HPSA thickness and exhibited the highest efficiency (12.13 %) at 1.5 nm, which is much higher than ca. 7.7 % in the case of 1.5 nm-thick pristine bPEI layers. The improved performance of solar cells was correlated with surface morphology and wetting characteristics, electrode work function change and coverage effect by X-ray photoelectron spectroscopy, and device stability after 60-day storage.

Numerical Simulation of High-Performance CsPbI3/FAPbI3 Heterojunction Perovskite Solar Cells

To broaden the absorption spectrum of cells, enhance the cell stability, and avoid high costs, a novel perovskite solar cell (PSC) with the structure of fluorine-doped tin oxide (FTO)/ZnO/CsPbI3/FAPbI3/CuSCN/Au is designed using the solar cell capacitance simulator (SCAPS) software. The simulation results indicate that the CsPbI3/FAPbI3 heterojunction PSC has higher quantum efficiency (QE) characteristics than the single-junction CsPbI3-based PSC, and it outputs a higher short-circuit current density (Jsc) and power conversion efficiency (PCE). In order to optimize the device performance, several critical device parameters, including the thickness and defect density of both the CsPbI3 and FAPbI3 layers, the work function of the contact electrodes, and the operating temperature are systematically investigated. Through the optimum analysis, the thicknesses of CsPbI3 and FAPbI3 are optimized to be 100 and 700 nm, respectively, so that the cell could absorb photons more sufficiently without an excessively high recombination rate, and the cell achieved the highest PCE. The defect densities of CsPbI3 and FAPbI3 are set to 1012 cm−3 to effectively avoid the excessive carrier recombination centering on the cell to increase the carrier lifetime. Additionally, we found that when the work function of the metal back electrode is greater than 4.8 eV and FTO with a work function of 4.4 eV is selected as the front electrode, the excessively high Schottky barrier could be avoided and the collection of photogenerated carriers could be promoted. In addition, the operating temperature is proportional to the carrier recombination rate, and an excessively high temperature could inhibit Voc. After implementing the optimized parameters, the cell performance of the studied solar cell was improved. Its PCE reaches 28.75%, which is higher than most of existing solar cells. Moreover, the open circuit voltage (Voc), Jsc, and PCE are increased by 17%, 9.5%, and 25.1%, respectively. The results of this paper provide a methodology and approach for the construction of high-efficiency heterojunction PSCs.

Schottky barrier heights and mechanism of charge transfer at metal-Bi2OS2 interfaces

Strong Fermi-level pinning (FLP) always occurs at the two-dimensional (2D) semiconductor-metal interface due to the complex interfacial charge transfer. By using monolayer (ML) Bi2OS2, an emerging 2D semiconductor with the highest electron mobility, the Schottky barrier heights (SBHs) and origin of charge transfer at Bi2OS2-metal interfaces are systematically studied based on density functional theory calculations. In 3D metal-Bi2OS2 interfaces, the formation of chemical bonding and the effect of Pauli exchange repulsion are found to be responsible for the strong interfacial charge transfer, resulting in strong FLP, and the direction of charge transfer induced by the two factors is opposite. Besides, an extra interfacial charge transfer is expected to equilibrate the Fermi level when the work functions (WFs) of metal electrodes are out of the range of electron affinity energy and ionization energy of semiconductors. For 2D metal-ML Bi2OS2 interfaces, surprisingly, the FLP is found to be entirely suppressed, and thereby, the 2D metal-Bi2OS2 contacts obey the conventional Schottky-Mott model. Such intriguing behavior arises from the 2D metal electrodes chosen in this work can effectively shield the effect of Pauli exchange repulsion. Consequently, wide-range and linear-tunable SBHs can be obtained and the conversion from n-type Ohmic contact to p-type Ohmic contact can be achieved by using 2D metal electrodes with different WFs. This study not only provides a theoretical foundation for selecting favorable metal electrodes in devices based on ML Bi2OS2, but also helps to enhance the understanding of the mechanism of interface interaction between metals and 2D semiconductors.

Charge Transfer Dynamics of Doped Graphene Electrodes for Organic Light-Emitting Diodes.

Atomically thin graphene has attracted immense attention as a future transparent electrode for flat-panel displays owing to its excellent conductivity, optical transparency, and flexibility. In particular, a graphene doping process is essential for implementing graphene-based high-performance devices, and the development of a transparent cathode with a low work function is required to simplify the integration process of thin-film transistors and organic light-emitting diodes (OLEDs) into active matrix displays. In this study, a transparent n-doped graphene cathode is proposed for implementing inverted OLEDs through two types of cesium (Cs)-based doping techniques: a dipping method using wet chemicals and an evaporation method under a vacuum atmosphere. The changes in the chemical structures and work functions of the n-doped graphene electrodes, as well as their surface morphologies and transmittances, were systematically investigated. The n-type doping mechanism of graphene was investigated, and a close relationship between the electrical charge transfer characteristics of graphene transistors and the formation of C-O-Cs complexes was revealed. Finally, an effective Cs-doped graphene electrode was developed, exhibiting a dramatically decreased work function while maintaining high transmittance; therefore, the Cs-doped graphene cathode was successfully integrated with inverted OLEDs with a bottom-light emission structure that exhibited enhanced external quantum efficiency of graphene cathode-based OLEDs. Thus, our findings provide a better understanding of the doping strategies and potential of n-doped graphene as a transparent cathode for developing high-performance future displays.

Design and performance augmentation of charge-plasma nanoFET with parametric analysis using non-equilibrium Green's function

Along with the expensive fabrication process, ultra-small devices suffer from short channel effects as well; hence, it is suitable to simulate before fabrication but modern simulators lack inclusion of quantum parameters. In this work, charge plasma-based nanoFET on insulator has been analyzed using NEGF. Behavior of the device is briefed using quantum parameters like density of states and transmission probability. The device is analyzed against physical variations, such as variation in electrode work function, variation in gate dielectric and thickness of body insulator. With Hafnium as source electrode and Palladium, Copper as gate and drain electrode respectively, investigated device resulted in IOFF of 1.94 × 10−13 A/μm and high ION/IOFF of 7.62 × 108. For the aforementioned optimum parameters, a low DIBL of 0.13 mV/V was observed. Incorporation of quantum effects heightens the precision of the device and hence, the analyzed device can be used for future applications.

The influence of top electrode work function on the performance of methylammonium lead iodide based perovskite solar cells having various electron transport layers

Perovskite solar cells (PSCs) have received much attention due to their low manufacturing cost and high conversion efficiency. Charge transport layer present in PSC helps extract photo-generated charge carriers. Although abundant research has been done in finding suitable charge transport layers, there are still many scopes to study the different charge transport layers. This work presents a theoretical study of PSCs with five different electron transport layers (ETLs) used independently and also as stack while also varying the top electrode (cathode) work function to determine its influence on the overall performance of PSCs with different ETLs. Our result shows stacked TiO2/PCBM ETL devices are more resistant structure to variations in the cathode work function. Jsc is independent of electrode work function for all ETLs. Voc remains unaffected for almost all ETLs until the electrode work function of 4.8 eV. Fill factor and conversion efficiency depends on ETL and electrode work function. As the cathode work function is increased, at the FTO/ETL interface, electric field initially pointing from FTO to ETL is gradually changing and pointing from ETL to FTO. The former favours electron transport and the latter un-favour electron transport from ETL to FTO. Therefore, fill factor and efficiency decreased as the work function is increased. Devices with TiO2, SnO2, ZnO, WO3, and SrTiO3 yielded maximum efficiencies of about 26%, 27.5%, 27.5%, 27%, and 27%, respectively. Our result shows electric field at the FTO/ETL interface and cathode work function determines the device performance. This work provides new insights into PSC and paves way for improving performance.

Impact of Coulomb scattering on argon plasma based thermionic converter performance

Particle-in-cell (PIC) simulations were performed to study the impact of Coulomb scattering on the performance of argon plasma based thermionic converters. Using a simplified model, studies from the 1970’s concluded that plasma resistance resulting from Coulomb collisions shifts the IV-curves of thermionic converters that use plasmas to mitigate space charge, thereby strongly limiting their electricity generation capability. In this work the impact of Coulomb collisions in such devices were studied as a function of the relative electrical potential between the electrodes, with higher fidelity than earlier models, using a fully kinetic approach (PIC-MCC with grid based electron–ion scattering). This approach overcomes the incorrect assumption in earlier models that the electron temperature is equal to the cathode temperature in all operating conditions. The fully self-consistent results presented here showed an increase in electron temperature with an increase in gap distance or electrode bias, which decreases the plasma resistivity. It was consequently found that earlier reports overestimated the negative impact of Coulomb collisions at the maximum power point, suggesting the practical usefulness of such devices is higher than previously believed. Electronic conversion efficiency higher than 15% was shown to be feasible at 1200 °C cathode temperature with reasonable electrode work-functions.

New metric for carrier selective contacts for silicon heterojunction solar cells

Heterojunction carrier selective contacts for solar cells have gained great attention because of the ability of these contacts to efficiently collect majority carriers while hindering the recombination of minority carriers, thus resulting in the highest reported voltage among crystalline silicon technologies. The electrode work-function, doping and thickness of the doped layer remain the key parameters for governing the cell performance. Recently, we have studied the requirements for carrier selective contacts under various illumination levels and reported logarithmic dependence of these parameters. In this work, we define a new metric for describing the ability of a contact to collect the carriers and named it as contact strength. We have developed an analytical approach for contact strength of hole selective contacts which represents the requirements on doping, thickness of the contact layer, and electrode work-function for a given illumination. First, the numerical model is calibrated with the experimental data for a wide range of illumination (0.01 Sun – 1.0 Sun) and then simulations have been fitted with analytical model. For the selective contact layer, we observe that only the total charge, rather than thickness and doping individually, matters. The work-function of the top electrode also contributes strongly to contact strength and can in principle substitute doped layer. This insightful metric will guide the solar cell technologists to better understand the carrier selective contacts and to maximize the cell performance not only at standard test conditions (STC), but also at low light illuminations.

Passivating the Interfacial Chemical Reaction via Self‐Assembly Layer for Efficient and Stable Inverted Nonfullerene Organic Solar Cells

The popular nonfullerene acceptors readily react with the amine group‐containing low‐work‐function interfacial layer (polyethylenimine [PEI] or polyethylenimine ethoxylated [PEIE]), leading a severe “S” shape in the current density–voltage (J–V) characteristics of the nonfullerene organic solar cells (OSCs). Herein, a novel strategy is proposed to passivate this detrimental interfacial chemical reaction. Phenol (Ph) is anchored on the surface of PEI to form a thin and dense self‐assembly layer, which can avoid a direct contact between the PEI and active layer. Moreover, the formed PEI–Ph bilayer cathode interface layer (CIL) can still low the work function of the bottom electrode. As a result, significant enhancement of the device performance is obtained for the PEI–Ph CIL‐based nonfullerene OSCs and the “S” shapes in the J–V characteristics are removed. After Ph anchoring on the surface of PEI, the power conversion efficiencies are increased from 2.46% to 11.97% for the PTB7‐Th:IEICO‐4F active layer system and from 6.09% to 16.34% for the PM6:Y6 system, respectively. More importantly, the PEI–Ph CIL‐based device displays a superior long‐term and illumination stability.

MoS2 Transistor with Weak Fermi Level Pinning via MXene Contacts

AbstractThe quality of the contact between source/drain electrodes and 2D transition metal dichalcogenides plays a decisive role in improving transistor performance. Understanding the mechanisms of Fermi level pinning (FLP) and finding out the strategies to solve FLP problems can further promote the development of 2D electronics. In this study, the suppressing effect of MXene on FLP in MoS2 transistors by using Ti3C2Tx as an electrode to build a Ti3C2Tx‐MoS2 heterostructure is systematically studied. A simple and time‐saving ultraviolet ozone technique to tune the work function of the Ti3C2Tx electrode in the range of 4.33–5.32 eV is proposed, and a low Schottky barrier height of 121 meV is achieved. The van der Waals contact between Ti3C2Tx and MoS2 can alleviate the FLP effectively, and the pinning factor can be greatly optimized from 0.28 (metal electrode) to 0.87 (MXene electrode). This study can pave the way for extensive use of MXene and provide a new strategy to eliminate the negative effects of FLP in 2D materials‐based electronic devices.

Electron Transport Layer-Free Ruddlesden–Popper Two-Dimensional Perovskite Solar Cells Enabled by Tuning the Work Function of Fluorine-Doped Tin Oxide Electrodes

Organic–inorganic halide two-dimensional (2D) layered perovskites have been demonstrated to have better environmental stability than conventional three-dimensional perovskites. In this study, we investigate the fabrication of electron transport layer (ETL)-free Ruddlesden–Popper 2D perovskite solar cells (PSCs) by tuning the work function of a fluorine-doped tin oxide (FTO) electrode. With the deposition of polyethylenimine (PEIE) onto its surface, the work function of the FTO electrode could be raised from −4.72 to −4.08 eV, which is more suitable for electron extraction from the perovskite absorber. Using this technique, the ETL-free 2D PSCs exhibited an excellent power conversion efficiency (PCE) of 12.7% (on average), which is substantially higher than that of PSCs fabricated on a pristine FTO electrode (9.6%). Compared with the PSCs using TiO2, the ETL-free PSCs could be fabricated under a low processing temperature of 100 °C with excellent long-term stability. After 15 days, the FTO/PEIE-based ETL-free PSCs showed a PCE degradation of 16%, which is significantly lower than that of the TiO2-based case (29%). The best-performing PSC using a FTO/PEIE cathode showed a high PCE of 13.0%, with a small hysteresis degree of 2.3%.

Ionic Liquid Gating in Perovskite Solar Cells with Fullerene/Carbon Nanotube Collectors

Metallic cathodes are one of reasons for instability in perovskite solar cells due to reaction with halogens I−, Br−, and it is desirable to have stable carbon‐based cathodes, particularly carbon nanotubes (CNTs), and transport layers such as C60/C70. In this work, we show that gating of such top CNT cathode in ionic liquid by changing gate voltage (V g) tunes the Fermi level of CNT by electrical double layer charging and causes lowering of the barrier at C60/C70 electron transport layer (ETL). Moreover, at higher V g the ions further propagate into fullerene ETL by electrochemical n‐doping, which increases dramatically performance by further raising mostly two parameters: short‐circuit current and fill factor, resulting in solar cell efficiency growth from 3% to 11%. Surprisingly, open‐circuit voltage (V oc) is not sensitive to V g in the perovskite solar cells, on the contrary to strongly enhanced V oc in ionically gated organic solar cells, where it is the main effect for ionic gating. This insensitivity of V oc to lowering of the work function of CNT electrode is a clear indication that V oc in the perovskite solar cell is determined by inner p‐i‐n junction formation in the perovskite layer itself.

Numerical simulation and performance optimization of GeSe based thin film solar cell with NiO as back surface field layer

Germanium monoselenide (GeSe) has emerged as a viable candidate for absorber material in thin film solar cell (TFSC) due to its favorable material characteristics. Herein, the novel GeSe based TFSC with CdS as buffer layer and NiO as back surface field (BSF) layer has been proposed and its photovoltaic performance has been evaluated theoretically using wxAMPS software. The device output parameters have been assessed by varying thickness and carrier concentration for the GeSe layer, CdS layer and NiO layer, respectively. Moreover, the defect densities in GeSe absorber layer, CdS/GeSe and GeSe/NiO interface layers, and the work function of metal electrode at the cell rear side have been altered to evaluate the photovoltaic characteristics. Conversion efficiency of 31.37% has been obtained for the proposed GeSe-based TFSC with the new architecture under the conditions such as the thicknesses of the CdS layer, GeSe layer and NiO layer are optimized to be 0.03 μm, 0.3 μm and 0.05 μm, respectively; the carrier concentrations of the CdS layer, GeSe layer and NiO layer are optimized to be 1018 cm−3, 1019 cm−3 and 1020 cm−3, respectively; the defect densities in the GeSe layer, IDL1, IDL2 both are set to be 1015 cm−3. These results suggest that GeSe can be employed as the promising absorber layer to fabricate low-cost and high efficiency TFSC.

(Digital Presentation) Study on the Electrical Characteristics and Band Diagrams of Ga2O3 MOS Gate Stacks

β-Ga2O3 is expected as one of the candidate materials for high-efficient and cost-effective power devices for high-voltage applications [1]. For the fabrication of MOSFETs the understanding of band diagrams of MOS structure is inevitably important. However, the previous reports on band alignments of β-Ga2O3 and various dielectrics including Al2O3 and SiO2 are controversial with significant inconsistencies in their values [2]. Since the ideal band diagram referring to the vacuum level is not clarified we cannot tell the Fermi level of β-Ga2O3 and the flat-band voltage (Vfb) shift of MOS capacitors. In this study we fabricated MOS structures and its band diagram was investigated from photoelectron spectroscopy.We employed SiO2 as the gate dielectric. Single crystalline β-Ga2O3 (001) wafers with ~2×1016 cm-3 n-type doped epitaxial layers were cleaned in diluted HF solution. Then SiO2 films were deposited by electron-beam evaporation of Si in O2 ambient of ~1×10-2 Pa, followed by post-deposition annealing (PDA) in 1 atm-O2 at various temperatures. Au was evaporated as gate electrode to form MOS capacitors. Ultraviolet photoelectron spectroscopy (UPS) was conducted to determine the energy level of the valence band edge on the surface of β-Ga2O3 epitaxial layer referring to the vacuum level. The valence band spectrum of ~4nm-thick SiO2/β-Ga2O3 was also investigated by x-ray photoelectron spectroscopy to determine the valence band offset at the interface.From C-V characteristics of MOS capacitors with different PDA conditions, the higher PDA temperature was found to be beneficial to achieve nearly-ideal C-V characteristics. A negligibly-small hysteresis was obtained for the one fabricated with O2-PDA at 1000℃ [3]. The energy profiles of interface state density (Dit) were determined by conductance method for the samples of different PDA conditions. The values of Dit decreased for higher PDA temperature down to ~1010 cm-3 at the energy level of EC−0.2 eV [3]. These values are significantly lower than typically reported ones for ALD-Al2O3 MOS structures on β-Ga2O3 [4]. The additional annealing at low temperature at 400℃ works for the further reduction of hysteresis to less than 1 mV/nm.Next the band diagrams of the MOS structures were investigated. From the UPS spectra we could deduce the energy level of valence band edge referring to the vacuum level, from the difference between minimum (cut-off) and maximum edges of the obtained kinetic energy spectra of photoelectrons. We also evaluated the valence band offset from the deconvolution of the valence band XPS of thin SiO2/β-Ga2O3 stack. From the energy edge difference between the deconvoluted spectra corresponding to SiO2 and Ga2O3, respectively, the valence band offset ~1.1 eV was deduced, which is not conflicting with the estimated valence band edge energy of Ga2O3 and the well-reported valence band edge energy of SiO2. The conduction band edge energy was also estimated assuming the bandgap of β-Ga2O3 (4.7eV) [1]. Considering the Fermi-level of β-Ga2O3 with n-type doping of ~2×1016 cm-3 was approximated to be ~0.1 eV from the conduction band edge, the Fermi-level on the surface of β-Ga2O3 epitaxial layer after 1000℃ O2 annealing was estimated to be 3.6-3.7eV below the vacuum level [5]. Note that this value would be significantly smaller than the one simply estimated from the previously reported electron affinity of Ga2O3 [6].Finally the Vfb shifts were investigated for the MOS capacitors fabricated with O2 annealing at 1000℃ with various thicknesses, referring to the ideal flat-band voltage determined with the Fermi-level of β-Ga2O3 as discussed above and the work function of Au electrode which was also determined with UPS measurement. As a result, we found the most of the Vfb values were around the ideal flat-band voltage irrespective of the film thickness from 20 to 60 nm, which indicates a small density of fixed charges <2×1011 cm-2 [5].In conclusion, we found that SiO2/β-Ga2O3 (001) MOS capacitors showed nearly-ideal electrical characteristics with small fixed charge density by applying O2-PDA at 1000℃. The band diagram for the MOS stacks referring to the vacuum level was clarified by photoelectron spectroscopy, which enables us to understand the β-Ga2O3 MOS interface properties correctly.

Stable lead-free Cs4CuSb2Cl12 layered double perovskite solar cells yielding theoretical efficiency close to 30%

Perovskite solar cells in the last decade have dominated the field of photovoltaics and optoelectronics. However, the organic-inorganic perovskite light absorbers suffer from long-term stability, durability, and toxicity. This article explores the lead-free and stable Cs4CuSb2Cl12 layered double perovskite light absorber with n-type SnO2 and p-type CuSCN transport layers. Using the SCAPS-1D software package, 224 solar cells are analyzed with varying thickness, defect, and doping density of the subsequent films. The optimized Cs4CuSb2Cl12 perovskite solar cells show PCE of 29.71% and 29.61% power conversion efficiency, respectively, with and without p-type CuSCN. For real-time analysis of the Cs4CuSb2Cl12 perovskite solar cells, the variation of PCE pertaining to the operating temperature is evaluated. The bulk defect density and the thickness of the Cs4CuSb2Cl12 light absorber are critical factors in achieving high power conversion efficiencies in Cs4CuSb2Cl12 perovskite solar cells with p-type CuSCN. For CuSCN free solar cells, the work function of the counter electrode determines the efficiency of the Cs4CuSb2Cl12 perovskite solar cells.

Design of a CH3NH3PbI3/CsPbI3-based bilayer solar cell using device simulation

With lead-based light harvesters, perovskite solar cells (PSCs) have an efficiency of approximately 25.5%, making them a viable photovoltaic technology. The selection of the absorber materials for PSC in this work are (i) Cesium lead iodide (CsPbI3) with a 1.73eV bandgap as the first absorber layer, this halide imparts higher stability to perovskite solar cells (ii) CH3NH3PbI3 (MAPbI3) with a bandgap of 1.55eV is selected as the second absorber layer as this material provides better efficiency to the perovskite solar cells. SCAPS-1D simulation software is used to perform an efficiency analysis of perovskite-perovskite CsPbI3/MAPbI3 bilayer solar cell. For efficiency optimization of the perovskite-perovskite bilayer solar cell, we have tried to calibrate seven parameters of the cell. These parameters are (i & ii) selection of the electron and hole transport material (iii, iv & v) variation in the: defect density of bulk material, doping concentration and the thickness of absorber layers, (vi) variation in work function of front electrode (vii) varying interface defect density. After optimization, the efficiency (η) of bilayer PSC is estimated to be 33.54%. The other PV parameters observed in optimal efficiency condition are open-circuit voltage (VOC) = 1.34V, short-circuit current density (JSC) = 27.45 mA/cm2 and fill factor (FF) = 90.49%. The CsPbI3/MAPbI3 bilayer perovskite solar cell efficiency is roughly double the efficiency of single junction CsPbI3 or MAPbI3 PSC. Our analysis observed that the variation in the doping and defect density of narrow bandgap material profoundly impacts the efficiency of perovskite-perovskite bilayer solar cells compared to the wide bandgap material.

Numerical investigation of the Cu2O solar cell with double electron transport layers and a hole transport layer

In this paper, a model of the Cu2O solar cell with double electron transport layers (ETLs) and a hole transport layer (HTL) has been investigated by SCAPS. Compared to the single ETL of ZnO, the problem of low open circuit voltage of the Cu2O solar cells can be improved by introducing the double ETLs of Zn(O,S)/ZnS. Our simulation results show that the sulfur concentration of Zn(O,S) and the donor density in double ETLs have a significant effect on device performance. The optimum S/S + O ratio and the best donor density are 0.82 and 8 × 1017cm−3, respectively. Due to the formation of an electron reflector and back surface field (BSF), an enhancement in both short circuit current density and open circuit voltage can be realized by introducing an appropriate HTL, and the best HTL is CuI, showing an efficiency of 12.15%. Then, the work function of metal electrode, the Cu2O thickness, the defect density and the acceptor density of Cu2O absorber layer, and the defect density at the Cu2O interfaces have been systematically investigated. After optimization, the best device efficiency of 16.49% can be achieved. Our results have demonstrated a new high-efficiency structure for cuprous oxide solar cells.

Anodic oxidation effects at the copper/silicon oxide interface

We report on anodic oxidation effects in memristively switching Cu/SiO2/Pt and Cu/CuOx/SiO2/Pt Electrochemical Metallization Cells. In-depth x-ray photoelectron spectroscopy reveals the formation of a Cu-ion reservoir composed of Cu(OH)2 underneath the anode during oxidation. By using cyclic voltammetry partial redox reactions are observed both in SiO2- and CuOx/SiO2-based devices. From our analysis we conclude that the CuOx layer acts as a reservoir for Cu-ions, similar to the low work-function electrode in valance change mechanism devices, which acts a reservoir for oxygen vacancies. Integration of a CuOx layer may thus allow to tailor the resistive switching performance of cation based memristors.