Charge Transport In Materials Research Articles

Numerical study of inorganic Cs2TiBr6 solar cells with a double hole transport layers

The proposed Cesium Titanium Bromide (Cs2TiBr6) has piqued curiosity as an absorber layer for the next-generation renewable energy. This is especially due to their important properties such as high stability and nontoxicity. Nevertheless, the performance of solar cells based on this double-perovskite is still lower than methylammonium lead halide perovskite solar cells, which limited their commercialization in the real world. Up till now, the highest efficiency of the experimentally constructed PSC has been 3.28%, where Cs2TiBr6 was utilized as an absorber layer and both inorganic (TiO2) and organic (P3HT, C60) as charge transport materials. . In this work, Numerical modeling tools were used to optimize the active layer with the novel architecture Au /P3HT/CuSbS2/ Cs2TiBr6/TiO2/FTO using solar cell capacitance simulator (SCAPS-1D). The results obtained using double hole transport layers provide a higher efficiency for Cs2TiBr6 perovskite solar cell compared with the conventional structure.

Numerical development of lead-free Cs2TiI6-based perovskite solar cell via SCAPS-1D

Because of the toxicity and stability concerns, commercialization of lead-based perovskite solar cells (PSCs) is limited. Solar cells made entirely of Ti-based all-inorganic perovskite could be a viable answer to these issues. This paper is a theoretical paper on a perovskite solar cell (PSC) based on Cs2TiI6 using all-inorganic charge transport materials. We proposed a high performance perovskite solar cell (PSC) according to variables such as charge transport materials and its optimal thicknesses, absorber thickness, absorber defect density and interface defect density and working temperature. The optimal absorber thickness, Hole transport layer (HTL) thickness, and Electron transport layer (ETL) thickness are 500 nm, 50 nm, and 10 nm, respectively. After analyzing the other factors, we ended up with a high-performance PSC with a power conversion efficiency of 22.5% at room temperature and 22.84% at 270 K. These results are useful for the conception and manufacture of PSCs.

Exploration of charge transport materials to improve the radiation tolerance of lead halide perovskite solar cells

Towards the application of perovskite solar cells (PSCs) in space, we extensively investigated the effects of electron beam irradiation on binary-mixed PSCs with various hole- and electron-transport materials.

Copper coordination polymers with selective hole conductivity

Low-dimensional copper coordination polymers represent an alternative, unprecedented class of charge transport materials, comprised of molecular building blocks.

Optimization based on computational analysis of lead-free inverted planar photo-voltaic device structure using halide based double perovskite material

Owing to the appealing optoelectrical, mechanical, and physical properties, configurable bandgaps, good performance on opaque devices, and low manufacturing cost, Perovskites solar cells are found to be the best alternatives for semi-transparent photo-voltaic (PV) applications. The high absorption coefficient, high carrier mobility, and long carrier diffusion length are inherent features of many organic and inorganic halide perovskite solar cells. Most of the promising perovskite materials contain Lead (Pb) and hence they are toxic. Besides toxicity issues, the stability of these perovskite structures is another key challenge in the process of its commercial production. The performance of various lead-free active PV materials was studied and identified that Cesium–Titanium Halide materials can be a suitable alternate for lead-based perovskite materials. These promising Cs2TiX6 materials have a tunable bandgap between 1.4 eV and 2.3 eV and have balanced electron and hole diffusion lengths. Most of the conventional PSC structure consists of regular planar N-I-P structure and the commercial applications of such devices are bounded due to very high J-V hysteresis and the need for high temperature during fabrication. The primary objective of this work is to optimize and develop an eco-friendly, highly efficient, Cesium-Titanium based novel inverted PV cell structure with all in-organic charge transport materials. The solar cell simulation program, SCAPS – 1D simulator, was used for conducting the numerical study and tested various device structures for obtaining maximum efficiency. The variations in the performance of PV cell structure were analyzed while using assorted absorber materials and inorganic charge transport materials. After the SCAPS-1D based simulation study, a high-performance PSC structure, FTO / MoO3 / Cs2TiBr6 / SnO2 / Au, was obtained. The proposed inverted PV cell structure can produce an excellent power conversion efficiency of 15.68 %, short-circuit current density of 16.59 mA/cm2, an open circuit voltage of 1.1 V, and a fill-factor of 85.76 %.

Linear and second‐order nonlinear optical properties of non‐fullerene acceptor derivatives with A–D–A structure

AbstractIn this paper, in order to study the relationship between structure and performance, four new non‐fullerene acceptor (NFA) derivatives were designed based on the two reported NFA molecules BO‐4Cl and BTP‐S2 by replacing the benzothiadiazole unit with a less‐electron deficient benzotriazole unit and inserting another ethylene double bond between the central core and the terminal groups. Density functional theory (DFT) and Time‐dependent DFT were applied to investigate linear and nonlinear optical (NLO) properties, such as electronic structure, electronic absorption, reorganization energy, and the second‐order NLO properties. The investigation demonstrates that they are all narrow bandgap derivatives, the absorption spectrum extends to the near‐infrared region and using two ethylene double bond is the most effective way to reduce the energy gap, redshift the maximum absorption peak and the middle absorption band, and enhance second‐order NLO response. Considering the smaller electron and hole reorganization energy and the larger static first hyperpolarizability value, the studied NFA derivatives have great potential to become ambipolar charge transport materials and large second‐order NLO materials.

Numerical simulation of novel lead-free Cs3Sb2Br9 absorber-based highly efficient perovskite solar cell

In this paper, a novel Cs 3 Sb 2 Br 9 perovskite is presented for the absorber layer of perovskite solar cells (PSC). A planar structure as ITO/TiO 2 /Absorber/Spiro-OMeTAD/Au with Cs 3 Sb 2 Br 9 as a light harvesting material is numerically simulated using SCAPS-1D simulation software. Initially, the optimization is performed on the various material parameters of absorber layer such as thickness, bulk defect density, relative permittivity and bandgap. The obtained optimal values for these parameters are 1000 nm, 1 × 10 12 cm −3 , 10, and 2.0 eV, respectively. Finally, the proposed PSC structure with optimized absorber layer is achieved the maximum power conversion efficiency (PCE) of 15.69% whereas V OC as 1.31 V, J SC as 13.67 mA/cm 2 , FF as 87.61%, and QE of ∼100% at 390 nm wavelength near the visible range of solar spectrum. The obtained results of numerical simulations with Cs 3 Sb 2 Br 9 as absorber layer endorse the novel proposed PSC material as the main body of PSC and opens a better route towards the development of a cost effective, highly efficient (Pb) lead-free and environment friendly PSC. • A novel Cs 3 Sb 2 Br 9 absorber layer material is proposed for design of high efficiency lead-free perovskite solar cell. • Numerical analysis and optimization of novel absorber in proposed PSC structure is performed using SCAPS-1D to investigate the effect of bulk defect density, absorber thickness, energy bandgap and permittivity variations on PSC parameters. • A planar structure consisting of charge transport materials TiO 2 and Spiro-OMeTAD used as ETL and HTL, is simulated for the analysis. • The proposed PSC is promising and may offer the PCE of 15.69% with V OC of 1.31 V , J SC of 13.67 mA/cm 2 and FF of 86.78%.

Inkjet printed organic light-emitting diodes employing organometal-halide perovskite as hole transport layer

Due to their narrow spectrum and high photoluminescence quantum yield, organic-inorganic hybrid perovskite materials have become an important emitter for light-emitting diodes (LED). In addition to the perovskite emitters, other perovskite materials such as methyl lead ammonium chloride (MAPbCl3) with high charge mobility can potentially be used as excellent charge transport materials. In this work, phosphorescence LED devices in which MAPbCl3 was employed as hole transport layer (HTL) was designed and fabricated by inkjet printing (IJP) process. Ethanolamine was added to the poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate) hole injection layer (HIL) to control the crystallization process and to suppress the surface defects of MAPbCl3. In addition, polyethylene oxide was doped into MAPbCl3 to improve the printability and the quality of film formation. The ‘blurred interface’ concept was successively applied to enable for the first time the IJP of three layers (HIL, HTL and emitter layers) in the LEDs. The fabricated multilayer LEDs achieved the maximum external quantum efficiency of 8.9%, maximum current efficiency of 30.8 cd A−1, and maximum power efficiency of 10.7 lm W−1. A 40 × 40 mm2 OLED light emitting device was successfully fabricated by IJP technology.

Structural Templating of an Organic Solar Cell Absorber by Ellagic Acid To Tune Its Aggregation, Molecular Orientation, and Optical Properties

Structural templating with homogeneous template layers is one of the strategies for controlling the orientation of small molecular absorbers in the photoactive layer of an organic solar cell to increase its power conversion efficiency. A main challenge thereby is the energetic alignment of the template molecules to the photoactive and charge-transporting materials. In the present study, the effects of a cluster-like template layer of ellagic acid (EA) on the morphology and optical properties of side-chain-substituted dicyanovinyl quaterthiophene (DCV4T-Et2) thin films are discussed. In the monolayer regime, J-aggregation of DCV4T-Et2 is confirmed. Insertion of the EA template layer leads to an improved aggregation behavior and formation of J-aggregates in DCV4T-Et2 films near the EA interface. The orientation of DCV4T-Et2 molecules in 30 nm thick films changes from “edge-on” to “face-on” due to a π–π interaction between the flat-lying EA molecules and the DCV4T-Et2 molecules. The face-on orientation by templating is preserved in blend layers with C60, and a considerable increase in the crystallinity of the DCV4T-Et2 phase in the blend is induced. Organic solar cells based on templated DCV4T-Et2:C60 active layers exhibit more than a 50% increase in the efficiency compared to nontemplated active layers. The short-circuit current density and the fill factor are significantly improved. Although the energetic alignment of EA is not ideal, no additional open-circuit voltage losses were observed with templating, due to the cluster-like morphology of the EA layer. Our results demonstrate a cluster-like templating approach with the novel template molecule EA to tailor the molecular orientation, crystallinity, and consequently optical properties of organic semiconducting molecules without significant energetic losses favorable for use in organic electronics.

Chemical bath deposition of AgBiS2 films for visible and X-ray detection

AgBiS2 possesses high absorption coefficient from ultra-violet to near-infrared, decent charge transport and superior materials stability, which has emerged as a promising candidate in the field of optoelectronics. However, efficient AgBiS2-based devices are mostly based on AgBiS2 quantum dots and precursor methods, which require either long preparation time and complex synthetic steps or inert atmosphere protection. To address these issues, we developed a novel and facile chemical bath deposition approach to deposit highly crystallized, uniform AgBiS2 thin films with decent optoelectronic properties. We also fabricated AgBiS2 heterojunction photodetectors based on this method, and achieved high responsivity covering the whole range of visible and near-infrared, fast response speed of ∼960 ns, and high specific detectivity of 8 × 1011 Jones and outstanding device stability. More importantly, we first demonstrated the device performance under X-ray illumination and observed decent sensitivity, implying great potential for low-cost, solution-processable X-ray detectors.

On-Surface Synthesis and Characterization of Super-nonazethrene.

Beginning with the early work of Clar et al. in 1955, zethrenes and their laterally extended homologues, super-zethrenes, have been intensively studied in the solution phase and widely investigated as optical and charge transport materials. Superzethrenes are also considered to exhibit an open-shell ground state and may thus serve as model compounds to investigate nanoscale π-magnetism. However, their synthesis is extremely challenging due to their high reactivity. We report here the on-surface synthesis of the hitherto largest zethrene homologue-super-nonazethrene-on Au(111). Using single-molecule scanning tunneling microscopy and spectroscopy, we show that super-nonazethrene exhibits an open-shell singlet ground state featuring a large spin polarization-driven electronic gap of 1 eV. Consistent with the emergence of an open-shell ground state, high-resolution tunneling spectroscopy reveals singlet-triplet spin excitations in super-nonazethrene, characterized by a strong intramolecular magnetic exchange coupling of 51 meV. Given the paucity of zethrene chemistry on surfaces, our results therefore provide unprecedented access to large, open-shell zethrene compounds amenable to scanning probe measurements, with potential application in molecular spintronics.

Construct efficient CsPbI2Br solar cells by minimizing the open-circuit voltage loss through controlling the peripheral substituents of hole-transport materials

In order to further boost the photovoltaic performance of all-inorganic perovskite solar cells (PSCs), great efforts are needed to synergistically develop high-quality perovskite film and highly efficient charge transport materials. In view of the fact that large number of researchers have devoted to optimizing the crystal composition and crystallization kinetics, we chose to carry out the study from the perspective of hole transport layer. Herein, we designed and synthesized two low-cost fluorene terminal-modified hole transport materials (HTMs), termed YT-MPF and YT-FF. Moreover, through the modification of peripheral groups, the electrostatic surface potentials of HTMs are well regulated. The HTM YT-MPF with one peripheral fluorene arm on each side exhibits a more polarized structure, which facilitates the intermolecular interaction and hole hopping transport. Applied YT-MPF in CsPbI2Br based all-inorganic PSC, an impressive power conversion efficiency (PCE) of 16.0% with fairly high open-circuit voltage (Voc) of 1.29 V is obtained, outperforming that of the control devices based on traditional HTM PTAA (12.7%) and Spiro-OMeTAD (14.7%). Our research supplies an effective way to push up the performance of CsPbI2Br PSC.

Highly efficient Cesium Titanium (IV) Bromide perovskite solar cell and its point defect investigation: A computational study

Lead-free, halide-based perovskites are drawing appreciable attention for solar cell applications due to the non-toxic nature and stable performance in ambient environment. In this study, we investigated different facets of a Cesium Titanium (IV) Bromide (Cs 2 TiBr 6 ) perovskite solar cell (PSC) with ZnO and MoO 3 as charge transport materials. Upon numerical optimization of perovskite layer thickness, its defect density , and the interface defect density, we propose a highly efficient, practically realizable PSC with a power conversion efficiency of 18.15%. Besides, we investigated different point defects in Cs 2 TiBr 6 and the effect of their electronic band positions on the PSC performance. It is found that for Cs 2 TiBr 6 based PSC applications, the material processing of Cs 2 TiBr 6 is a crucial aspect and the PSC may underperform for deep defect states (0.2 eV ~ 1.6 eV) with defect density over 10 15 cm −3 . In addition, we analyzed different back contact materials and found that carbon-based back contact can be a low-cost solution to gold for Cs 2 TiBr 6 PSCs. • A Cesium Titanium (IV) Bromide (Cs 2 TiBr 6 ) based perovskite solar cell with FTO/ZnO/Cs 2 TiBr 6 /MoO 3 /Au structure is proposed. • An optimum power conversion efficiency (PCE) of 18.15% is achieved. • Investigation on possible point defects in Cs 2 TiBr 6 and their electronic band position's effect on the PSC performance. • For deep defect state (0.2 eV ~ 1.6 eV) and defect density over 10 15 cm −3 , the PSC tends to underperform. • Carbon-based back contact can be a possible low cost replacement of gold for Cs 2 TiBr 6 PSCs.

Enhancement in charge extraction and moisture stability of perovskite solar cell via infiltration of charge transport material in grain boundaries

Perovskite solar cells (PeSCs) attract significant attention owing to their numerous advantages such as superior optical/electrical properties and solution processability. However, the existence of defects in the grain boundaries still prevents high performance and stable PeSCs. Here, we present a simple yet effective momentary spinning (MS) method for passivating defect sites in the grain boundaries of PeSCs. By applying the MS method to the perovskite active layer, we achieve infiltration of p-type hole transporting materials (HTMs) with selective hole transport into grain boundaries, thereby reducing leakage current, suppressing nonradiative recombination loss, and achieving efficient hole extraction. The MS-fabricated PeSCs remarkably enhance device performance, displaying higher short-circuit current (Jsc), open-circuit voltage (Voc), and fill factor (FF) than the conventional spin-coating (SC) devices. The best device exhibits a Jsc of 23.2 mA cm−2, a Voc of 0.99 V, and an FF of 0.81, yielding a power conversion efficiency (PCE) of 18.6%. In addition, passivating hydrophilic grain boundaries with hydrophobic HTM improves the moisture stability of the device. When device performance is monitored for over 20 days of storage, the MS device exhibits improved stability with over 80% of the initial PCE compared to the SC device with only 50%.

Electro-optical and charge transport properties of chalcone derivatives using a dual approach from molecule to material level simulations

In this study, three chalcone derivatives with a basic skeleton of [1,100-biphenyl]-4-yl)-3-(3-nitrophenyl)prop-2-en-1-one are investigated. The basic skeleton was modified with the addition of three-terminal groups including hydrogen (1), methyl (2), and methoxy group (3). Using CASTEP Module, the optoelectronic properties are evaluated. The solid-state geometries of these systems are explored within the periodic boundary conditions (PBC). Among these systems, system 3 is found much better in terms of electron transport and optical properties such as dielectric function, absorption, conductivity, reflectivity, loss function, and refractive index. System 3 showed a higher dielectric function value about 3.7 at 1.8 eV thereby absorption 6.9 × 104 cm−1 at 300 nm and conductivity 1.2 fs−1 at 3.5 eV in the (001) plane. Furthermore, system 3 exhibited a high reflectivity and loss function in the (010) plane. Electronic band structure, the density of state, and electronic coupling analysis also reveal that system 3 has a potential application in charge transport devices. The study of electronic couplings that dominate the slowest electron hopping in a potential conductive path is roughly four to ten times larger for the holes than for the electrons. The transport pathways in systems 1 and 2 are 2D, while 1D in system 3. The bottleneck rate for electron transport is expected to be ~25 faster for system 3 than the other systems. This system 3 shows an excellent potential both at molecular and bulk levels for efficient charge transport material.

Diffusion in Organic Film Stacks Containing Solution-Processed Phosphorescent Poly(dendrimer) Dopants.

Efficient organic light-emitting diodes (OLEDs) consist of an emissive layer comprising a blend of a light-emitting and host material in contact with one or more charge transporting layers. The distribution of the active material in the guest-host emissive layer blend and the changes that may occur upon thermal annealing are two important factors in determining the stability and efficiency of OLEDs. We have combined neutron reflectometry and photoluminescence measurements to investigate the structures of films comprising an emissive layer containing a phosphorescent poly(dendrimer) material blended with 4,4'-N,N'-di(carbazolyl)biphenyl. This combination has been shown to give rise to highly efficient OLEDs. Here, we show that the emissive poly(dendrimer) material was not uniformly distributed in the host, but formed a concentration gradient within the emissive layer. Upon heating, the adjacent electron transport layer was found to intermix with the emissive layer, accompanied by changes in the material distribution in the emissive layer. The intermixing of the materials led to a decrease in the photoluminescence from the poly(dendrimer) within the film. The decrease in the photoluminescence was ascribed to an increase in interchromophore interactions that could arise from a conformational change of the poly(dendrimer) or phase separation leading to aggregation. The results indicate that, while uniform mixing of the guest and host is not essential for efficiency, the thermal stabilities of both host and charge transport materials are important for device durability.

Dendritic-Like Molecules Built on a Pillar[5]arene Core as Hole Transporting Materials for Perovskite Solar Cells.

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Nonhalide Materials for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) have witnessed great advancements in power conversion efficiency (PCE) and stability. Over the past several years, various nonhalide materials have been extensively developed to enhance both PCE and stability by including them in perovskite compositions, perovskite precursor materials, additives, post-treatment reagents, dopants for charge transport materials (CTMs), CTMs, and interfacial modifiers. In this review, various nonhalide materials reported for PSCs are described and the dependence of the photovoltaic performance on anions (or in part cations) in nonhalide materials is investigated. This review highlights the importance of synergistic and rational engineering of anions and cations of the nonhalide materials in order to maximize both PCE and stability of PSCs.

Materials Design and Optimization for Next-Generation Solar Cell and Light-Emitting Technologies.

We review some of the most potent directions in the design of materials for next-generation solar cell and light-emitting technologies that go beyond traditional solid-state inorganic semiconductor-based devices, from both the experimental and computational standpoints. We focus on selected recent conceptual advances in tackling issues which are expected to significantly impact applied literature in the coming years. Specifically, we consider solution processability, design of dopant-free charge transport materials, two-dimensional conjugated polymeric semiconductors, and colloidal quantum dot assemblies in the fields of experimental synthesis, characterization, and device fabrication. Key modeling issues that we consider are calculations of optical properties and of effects of aggregation, including recent advances in methods beyond linear-response time-dependent density functional theory and recent insights into the effects of correlation when going beyond the single-particle ansatz as well as in the context of modeling of thermally activated fluorescence.

Perspective on Predominant Metal Oxide Charge Transporting Materials for High-Performance Perovskite Solar Cells

Nowadays, the power conversion efficiency of organometallic mixed halide perovskite solar cells (PSCs) is beyond 25%. To fabricate highly efficient and stable PSCs, the performance of metal oxide charge transport layers (CTLs) is one of the key factors. The CTLs are employed in PSCs to separate the electrons and holes generated in the perovskite active layer, suppressing the charge recombination rate so that the charge collection efficiency can be increased at their respective electrodes. In general, engineering of metal oxide electron transport layers (ETLs) is found to be dominated in the research community to boost the performance of PSCs due to the resilient features of ETLs such as excellent electronic properties, high resistance to thermal temperature and moisture, ensuring good device stability as well as their high versatility in material preparation. The metal oxide hole transport layers in PSCs are recently intensively studied. The performance of PSCs is found to be very promising by using optimized hole transport materials. This review concisely discusses the evolution of some prevalent metal oxide charge transport materials (CTMs) including TiO2, SnO2, and NiOx, which are able to yield high-performance PSCs. The article begins with introducing the development trend of PSCs using different types of CTLs, pointing out the important criteria for metal oxides being effective CTLs, and then a variety of preparation methods for CTLs as employed by the community for high-performance PSCs are discussed. Finally, the challenges and prospects for future research direction toward scalable metal oxide CTM-based PSCs are delineated.