Charge Transport In Materials Research Articles

The Effect of Transient Power Ramp‐Up on Structural and Optical Properties of CuO Thin Films Prepared by Radio Frequency Magnetron Sputtering

Transition metal oxides have found application as charge transport materials (CTMs) in perovskite solar cell devices due to their better environmental stability and superior electronic properties compared to organic CTMs. Many researchers have used radio frequency (RF) magnetron sputtering to deposit inorganic CTMs on inorganic layers. However, such efforts on perovskites have been limited by the distortion of high‐energy ions of the sputtering gas energized by the RF power and temperature. The ions may also distort the interface between transparent conducting oxides and the charge transport layers, thereby increasing optical scattering. Thus, the effect of ramp power during RF magnetron sputtering deposition on the structural and optical properties of copper oxide thin films is investigated. While the optical transmittance of the films decreases with increased RF power, it remains the same for all ramped power films; however, it has a similar profile as the highest RF power film. As the ramp power increases, the X‐ray diffraction shows that the films become more polycrystalline with a monoclinic crystal structure. The energy‐dispersive X‐ray spectroscopy results reveal that the atomic concentration of copper slightly increases with the RF power, whereas oxygen concentration slightly decreases.

Performance prediction of perovskite solar cell integrated with lead-free cesium platinum Iodide (Cs2PtI6) absorber and CuInS2 quantum Dot as HTL

Lead-containing perovskite solar cells present significant obstacles to achieving widespread commercial implementation of problems related to their toxicity and stability. Hence, it is critical to contemplate Pt-based all-IPSC as indispensable for rapidly spreading high-performing PSCs. These last several years have witnessed a growing interest in PSCs employing all-inorganic perovskite absorbers, which have garnered plenty of attention arising from their low bandgap and broad high absorption. In this study, we comprehensively investigate a PSC based on Cs2PtI6 using SCAPS. We offer a hypothetical assessment of a Cs2PtI6-based n-i-p organized heterojunction PSC, which is well disposed of and stable without a lead because it utilizes all-inorganic charge-transporting elements. By carefully balancing the thickness of charge transport materials, absorber thickness, defective absorber density, the interface's defect density, series resistance, and shunt resistance, we have achieved a performance-driven PSC with an efficiency of up to 32.77 % at room temperature. Based on our findings, Cs2PtI6 displays excellent potential as an absorbing perovskite for advancing lower poisonous IPSC technology.

Hole and electron transport materials: A review on recent progress in organic charge transport materials for efficient, stable, and scalable perovskite solar cells

Charge transporting materials are essential for fabricating stable and efficient perovskite solar cells. The high-temperature processing, surface defects, and low mobility are common issues in inorganic charge transport materials which can hinder the fabrication of low-cost, efficient, and stable perovskite solar cells. Dopants increase the processing cost of the hole transport materials. Surface defects are observed in the high-temperature processed inorganic electron transport materials. There is a need to develop organic compounds for charge transportation in perovskite solar cells. Herein, the advancements in the organic materials for charge transport in the perovskite solar cells are reviewed. The low-cost processing, better solubility, efficient charge mobility, tunable molecular orbitals, and better stability of organic compounds are some properties for their utilization as charge transport materials in perovskite solar cells. Organic small molecules, polymers, and phthalocyanine compounds can be utilized as dopant-free hole transport materials. Fullerene and non-fullerene derivatives like C60, C70, azaacenes, indacenodithiophene, polymers, and rylene diimides are promising electron transport materials. The functionality, engineering, charge transport properties, and device characteristics of different organic materials are discussed. The review will offer a forecast for improving device stability and efficiency in terms of architecture, engineering, and materials to realize the commercialization of perovskite solar cells soon.

Comprehensive analysis of heterojunction compatibility of various perovskite solar cells with promising charge transport materials

The allure of perovskite solar cells (PSCs), which has captivated the interest of researchers, lies in their versatility to incorporate a wide range of materials within the cell’s structure. The compatibility of these materials plays a vital role in the performance enhancement of the PSC. In this study, multiple perovskite materials including FAPbI3, MAGeI3 and MASnI3 are numerically modelled along with the recently emerged kesterite (CBTS, CMTS, and CZTS) and zinc-based (ZnO and CdZnS) charge transport materials. To fully explore the potential of PSCs and comprehend the interplay among these materials, a total of 18 PSC structures are modeled from different material combinations. The impact of band gap, electron affinity, absorption, band alignment, band offset, electric field, recombination rate, thickness, defects, and work function were analyzed in detail through a systematic approach. The reasons for varying performance of different PSCs are also identified. Based on the simulated results, the most suitable charge transport materials are CdZnS/CMTS for FAPbI3 producing a power conversion efficiency (PCE) of 22.05%, ZnO/CZTS for MAGeI3 with PCE of 17.28% and ZnO/CBTS for MASnI3 with a PCE of 24.17%.

Numerical investigation of lead free Cs2TiBr6 based perovskite solar cell with optimal selection of electron and hole transport layer through SCAPS-1D simulation

Halide-based perovskite has several advantages, including high efficiency, ease of manufacture, and low cost. In general, hazardous lead (Pb) is used in perovskite solar cells as an absorber layer, while polymer, which is unstable in nature used as the electron/hole transport layer. Despite its appealing characteristics, the device uses of lead and degradable components must be addressed. Lead-free titanium-based inorganic perovskite solar cells (PSCs) have drawn strong scientific interest in recent years in order to reduce the possibly detrimental effects of lead on the environment. Titanium is non-toxic, robust, inexpensive, and widely available when compared to other elements. The performance of PSCs is simulated and optimized using the SCAPS-1D software. The effects of various parameters of ZnO and CuSbS2 as charge transport materials on the Cesium Titanium (IV) Bromide (Cs2TiBr6) perovskite solar cell were examined in this study. Results indicate that a highly efficient PSC with a power conversion efficiency (PCE) of 26.96 %, a Voc of 1.0476 V, and an FF of 81.36 % is achieved after numerically optimized the perovskite layer thickness, doping concentration,defect density,and other device input parameters. The observed results are very encouraging and show the potential of Cs2TiBr6 for efficient and environmentally friendly solar applications. The outcomes of this study are likely to not only improve understanding but also motivate further research into the lead-free perovskite solar cell.

A comparative numerical approach between lead-free inorganic Cs2TiBr6 and Cs2PtI6-based perovskite solar cells

Lead halide perovskite has drawn much interest recently because of its impressive optoelectronic performance and unique characteristics. However, concerns regarding its toxicity and instability have hindered the complete industrialization of this material. We propose and investigate the performance of lead-free, eco-friendly, inorganic perovskite solar cells (PSCs) based on Cs2TiBr6 and Cs2PtI6 absorbers in this study. The investigation involved the examination of several parameters, including absorber thicknesses, absorber defect densities, and charge transport material thicknesses. Our findings indicate that Cs2PtI6-based PSCs exhibit superior performance, with an efficiency of 24.49%. In comparison, it is found that the efficiency of PSCs based on Cs2TiBr6 is just 9.81%. The study provides valuable insights into the design of high-performance PSCs for commercial exploitation.

Challenges and Strategies Toward Future Stable Perovskite Photovoltaics

In recent years, perovskite solar cells (PSCs) have received widespread attention due to their superior photovoltaic performance. However, perovskite materials and related films/devices all suffer unfavorable instability issues, which largely hamper their commercialization. In this review, research status, main challenges, and possible strategies to overcome the instability issues in PSCs are comprehensively presented and discussed from four main perspectives, including perovskite, charge transport materials, electrodes, and encapsulations. Related testing standards to accurately evaluate PSC lifetime are also summarized to provide essential guidance toward future advancement of stable PSCs.

Current State and Future Perspectives of Printable Organic and Perovskite Solar Cells.

Photovoltaic technology presents a sustainable solution to address the escalating global energy consumption and a reliable strategy for achieving net-zero carbon emissions by 2050. Emerging photovoltaic technologies, especially the printable organic and perovskite solar cells, have attracted extensive attention due to their rapidly transcending power conversion efficiencies and facile processability, providing great potential to revolutionize the global photovoltaic market. To accelerate these technologies to translate from the laboratory scale to the industrial level, it is critical to develop well-defined and scalable protocols to deposit high-quality thin films of photoactive and charge-transporting materials. Herein, the current state of printable organic and perovskite solar cells is summarized and the view regarding the challenges and prospects toward their commercialization is shared. Different printing techniques are first introduced to provide a correlation between material properties and printing mechanisms, and the optimization of ink formulation and film-formation during large-area deposition of different functional layers in devices are then discussed. Engineering perspectives are also discussed to analyze the criteria for module design. Finally, perspectives are provided regarding the future development of these solar cells toward practical commercialization. It is believed that this perspective will provide insight into the development of printable solar cells and other electronic devices.

Solution Processed Light Emitting Diode Based on InP Quantum Dots with Hybrid Emissive Layer

Solution-processable Cadmium-based Quantum dots light emitting diodes (QLEDs) are regarded as a good candidate for good performance display devices due to excellent color purity and inexpensive production. However, the toxicity still poses a severe risk. Although the most effective cadmium-free substance is thought to be InP for producing efficient QLEDs, its efficiency falls far short of its cadmium-based counterparts. We made a homogeneous thin film by mixing the organic compound 4, 4-bis (N-carbazyle)-1, 1-biphenyl (CBP) with InP/ZnSe quantum dots (QDs). Then, in our QLED design, we utilized this film as an emissive layer. The new QDs-based device showed a higher luminance of 14600 cd/m2 and having higher external quantum efficiency (EQE) of 11.6%. We discovered that the mixed QDs without any phase separation had a consistent distribution of CBP, which facilitated transfer of energy to QDs and injection of holes into the emissive layer. The blended QD was also shown to restrict injection of electrons into the hole transport/injection layers, protecting the device’s structural integrity. Developing a balanced charge in stable optoelectronic devices densities has a high potential when a homogeneous QD layer is combined with an effective charge transport material.

Symmetry-Breaking Charge Separation in a Chiral Bis(perylenediimide) Probed at Ensemble and Single-Molecule Levels.

Chiral molecular assemblies exhibiting symmetry-breaking charge separation (SB-CS) are potential candidates for the development of chiral organic semiconductors. Herein, we explore the excited-state dynamics of a helically chiral perylenediimide bichromophore (Cy-PDI2) exhibiting SB-CS at the ensemble and single-molecule levels. Solvent polarity-tunable interchromophoric excitonic coupling in chiral Cy-PDI2 facilitates the interplay of SB-CS and excimer formation in the ensemble domain. Analogous to the excited-state dynamics of Cy-PDI2 at the ensemble level, single-molecule fluorescence lifetime traces of Cy-PDI2 depicted long-lived off-states characteristic of the radical ion pair-mediated dark states. The discrete electron transfer and charge separation dynamics in Cy-PDI2 at the single-molecule level are governed by the distinct influence of the local environment. The present study aims at understanding the fundamental excited-state dynamics in chiral organic bichromophores for designing efficient chiral organic semiconductors and applications toward charge transport materials.

Morphological, Photoluminescence, and Electrical Measurements of Rare-Earth Metal-Doped Cadmium Sulfide Thin Films.

This work is aimed at investigating the viability of utilizing cadmium sulfide (CdS) as a buffer layer in CdTe solar cells by analyzing and assessing its optical, photoluminescence, morphological, and electrical properties. These films were fabricated using a thermal coating technique. Optical microscopy was used to observe the changes in morphology resulting from the doping of rare-earth metals such as samarium (Sm) and lanthanum (La) to CdS, while the granular-like structure of the sample was confirmed by scanning electron microscopy. The objective of incorporating Sm and La ions into CdS was to enhance photoconductivity and optimize the optical bandgap, aiming to create a viable charge transport material for photovoltaic devices with enhanced efficiency. Through that process, a noticeable decrease in transmission, from approximately 80 to 68% in the visible region, was observed. Additionally, the bandgap value was reduced from 2.43 to 2.27 eV. Furthermore, during the analysis of the photoluminescence spectra, it was observed that emission peaks occurred in the visible region. These emissions were attributed to electronic transitions that took place via band-to-band and band-to-impurity interactions. The electrical measurements showed an enhancement in conductivity due to the decrease in the bandgap. This notable consequence of the doped materials suggests their utilization in photovoltaic systems.

Microwave-assisted synthesis of thiazolothiazole-containing conjugated polymers as promising charge-transport materials for perovskite solar cells

The synthesis of novel thiazolo[5,4-d]thiazole-containing conjugated polymer was performed by three alternative methods, namely, by the Stille or Suzuki cross-coupling as well as microwave-assisted condensation reaction with carbonyl precursor and dithioxamide. The latter way is straightforward and efficient for the design of novel materials with desirable optoelectronic and physicochemical characteristics providing an encouraging hole-transport properties and comparable performance of perovskite solar cells.

(Invited) Record-High Charge Carrier Mobilities in 2D Covalent- and Metal- Organic Frameworks

Organic based 2D layered materials (2DLMs) including 2D covalent and metal organic frameworks (COFs and MOFs) are promising candidates for traditional applications in gas storage and separation as well as catalysis. This is due to the long-range crystalline order that can be achieved in them as well as their tunable porosity and chemistry. Synthetic chemistry efforts aiming an enhanced coupling between their building block constituents have recently led to the design of (semi-)conducting MOFs and COFs displaying high conductivities and record charge carrier mobilities. These achievements have opened the path for their application in opto-electronics. Yet, despite being a critical aspect for the development of 2DLM based electronics, understanding the true nature of charge transport in these novel materials by stabilising reliable structure-property-function relations is largely unexplored.Here I will present time-resolved high-frequency (terahertz) conductivity studies of state-of-the-art organic based 2DLMs materials revealing semiconducting behaviour and record charge carrier mobilities. First, I will present a detailed characterization for the electronic properties of Zn– and Cu–phthalocyanine-based pyrazine-linked 2D COFs [1,2]. These 2D COFs, synthesized by condensation of metal–phthalocyanine (M = Zn and Cu) and pyrene derivatives, are obtained as polycrystalline-layered semiconductors displaying p-type doping and a band gap of ∼1.2 eV. Hall effect measurements (dc limit) and terahertz (THz) spectroscopy (ac limit) in combination with density functional theory (DFT) calculations demonstrate that varying metal center from Cu to Zn in the phthalocyanine moiety has a negligible effect in the conductivity (∼5 × 10–7 S/cm), charge carrier density (∼1012 cm–3), charge carrier scattering rate (∼3 × 1013 s–1), and effective mass (∼2.3m0) of majority carriers (holes). However, both samples reveal slightly different mobilities that can be attributed to charge carrier localization at crystalline grain boundaries. Furthermore we analyse the effect of iodine doping on the Zn based 2D COFs. The resultant 2D c-COF ZnPc-pz-I2 maintains its structural integrity and displays enhanced conductivity by 3 orders of magnitude, as a result of improved charge carrier concentrations. Hall effect reveal a charge carrier mobility reaching ∼22 cm2/Vs for ZnPc-pz-I2, which represent a record value for 2D c-COFs. An improved mobility upon doping can be traced to an increase in scattering time for free charge carriers, indicating that scattering mechanisms limiting the mobility are mitigated by doping.In the second part of my talk, I present the results concerning a Fe3(THT)2 (THT=2,3,6,7,10,11-hexathioltriphenylene) 2D MOFs [3]. The π-d conjugated samples, synthesized through interfacial method at room temperature, are obtained as a large-area, free-standing films with tunable geometry (size and thickness). The Fe3(THT)2 films are porous (specific surface area of 526±5 m2/g) and semiconducting (with a ~250 meV direct bandgap), and remarkably display band-like charge transport. This finding is directly demonstrated from the Drude-type high-frequency (terahertz) photo-conductivity response obtained in the samples; revealing free-moving, delocalized charge carriers displaying ~220 cm2/Vs mobilities at room temperature; a record charge carrier mobility for MOFs. The temperature dependence of the mobility reveals that the main scattering mechanism limiting the mobility and hence band-like charge transport in this material is related to impurity scattering, so that material improvements may further increase the mobility.The demonstration of band-like charge transport and record-high mobilities in semiconducting 2D COFs and MOFs reveal the potential of (porous) electrically conductive 2DLMs to be employed as active materials in opto-electronics devices.

Computational Insight into Electronic, Optical and Photophysical Properties of Small Compounds for Solar Cell Applications

Thiophene-based small molecules COMP.1 and COMP.2 are explored for optical, electronic and photophysical properties by using theoretical approach. The density functional theory (DFT) at B3LYP/6-31G** level of theory is used to optimize both molecules COMP.1 and COMP.2 at ground state, while for excited state, the time-dependent DFT (TD-DFT) is utilized at the same level of theory. The optoelectronic and photophysical parameters specify that these materials would be good charge transport materials. Computed global reactivity descriptors indicate that COMP.2 T is more stable exhibiting smaller chemical reactivity. High electron mobility of COMP.1 as 0.78[Formula: see text]cm[Formula: see text]V[Formula: see text]s[Formula: see text] revealing that COMP.1 might be good n-type material. COMP.1 has been anticipated to be a decent n-type material as compared to COMP.2 and might be good material for solar cell applications.

Performance optimization of a CsGeI3-based solar device by numerical simulation

Germanium-based halide perovskites (CsGeI3) are good absorbers materials for eco-friendly perovskite solar devices. In this work, a numerical analysis via SCAPS-1D software, is done to enhance the performance of a device already experimentally realized (FTO/TiO2/CsGeI3/Spiro-OMeTAD/Ag). After selecting SnO2 and CuI as best Charge transport materials (CTMs) in front of others, we have optimized their thicknesses, we investigated the impact of: CsGeI3 thickness, its defect density (Nt), its acceptor concentration, CuI doping density, SnO2 doping density, SnO2/CsSnI3 defect density, CsSnI3/CuI defect density, also the impact of shunt resistance, series resistance, and temperature. Finally, we have achieved a new solar device based on CsGeI3, with a fully inorganic FTO/ SnO2/CsGeI3/CuI/Ag structure. The final output parameters are PCE = 15.68 %, FF = 73.45 %, JSC = 22.56 mA/cm2 and VOC = 0.946 V at room temperature. The results are beneficial for the design and manufacture of CsGeI3-based solar devices.

Role of cations in the photovoltaic performance optimization of ternary stannates, MSnO3 (M = Ca, Sr, and Ba) and N2SnO4 (N = Ca, Sr, Ba, and Zn)

Given the tremendous interest in next-generation photoelectric conversion devices, such as tandem solar cells, indoor photoelectric conversion devices, and image sensors, the development of device-specific electron transport materials is essential for achieving high performance. Sn-based semiconductors are one of the edge materials with the potential to satisfy these requirements. In particular, ternary stannate compounds have shown high potential as electron transport electrodes in several impressive studies. However, systematic research on the electronic band structure and chemical bonding characteristics of these materials remains insufficient. In this study, we present the effect of cations on the crystal structure and electronic band structure of ternary stannate compounds, MSnO3 (MSO, M = Ca, Sr, and Ba) and N2SnO4 (N2SO, N = Ca, Sr, Ba, and Zn). Additionally, their potential as electron transport electrodes is verified by application in dye-sensitized solar cells (DSCs). Notably, although BaSnO3 (BSO) and Zn2SnO4 (Z2SO) had inferior dye adsorption properties, they exhibited higher overall performance in DSCs than the other stannate compounds. The origin of the excellent performances of BSO and Z2SO is attributed to their supportive electronic band features, including the lower flat-band potential and conduction band than that of the lowest unoccupied molecular orbital level of N719 dye and excellent charge transport property. This study highlights the decisive impact of the electronic band structure and charge transport ability of stannate compounds on the photoelectric conversion performance and provides design guidelines for developing new charge transport materials.

Recoverable Flexible Perovskite Solar Cells for Next-Generation Portable Power Sources.

Flexible perovskite solar cells (FPSCs) with excellent recoverability show a wide range of potential applications in portable power sources. The recoverability of FPSCs requires outstanding bendability of each functional layer, including the flexible substrates, electrodes, perovskite light absorbers, and charge transport materials. This review highlights the recent progress and practical applications of high-recoverability FPSCs, and illustrates the routes toward improvement of the recoverability and environmental stability through the choice of flexible substrates and the preparation of high-quality perovskite films, as well as the optimization of charge-selective contacts. In addition, we explore the intrinsic properties of each functional layer from the physical perspective and analyze how to select suitable functional layers. Additionally, some effective strategies are summarized, including material modification engineering of selective contacts, additives and interface engineering of interlayers, which can release mechanical stress and increase the power-conversion efficiency (PCE) and recoverability of the FPSCs. The challenges of making high-performance FPSCs with long-term stability and high recoverability are discussed. Finally, future applications and perspectives for FPSCs are discussed, aiming to promote more extensive commercialization processes for lightweight and durable FPSCs.

Recoverable Flexible Perovskite Solar Cells for Next‐Generation Portable Power Sources

AbstractFlexible perovskite solar cells (FPSCs) with excellent recoverability show a wide range of potential applications in portable power sources. The recoverability of FPSCs requires outstanding bendability of each functional layer, including the flexible substrates, electrodes, perovskite light absorbers, and charge transport materials. This review highlights the recent progress and practical applications of high‐recoverability FPSCs, and illustrates the routes toward improvement of the recoverability and environmental stability through the choice of flexible substrates and the preparation of high‐quality perovskite films, as well as the optimization of charge‐selective contacts. In addition, we explore the intrinsic properties of each functional layer from the physical perspective and analyze how to select suitable functional layers. Additionally, some effective strategies are summarized, including material modification engineering of selective contacts, additives and interface engineering of interlayers, which can release mechanical stress and increase the power‐conversion efficiency (PCE) and recoverability of the FPSCs. The challenges of making high‐performance FPSCs with long‐term stability and high recoverability are discussed. Finally, future applications and perspectives for FPSCs are discussed, aiming to promote more extensive commercialization processes for lightweight and durable FPSCs.

The performance of a lead-free Cs2TiBr6 based solar cell with diverse charge transport material and back metal contacts

The performance of a lead-free Cs2TiBr6 based solar cell with diverse charge transport material and back metal contacts

Performance evaluation and the optimization of an inverted photo-voltaic cell with lead-free double perovskite material and inorganic transport layer materials

The research on the solar cell structure based on various inorganic, organic and hybrid type of perovskite absorbing materials is increasing due to their legion features. Various inorganic titanium (Ti) based double perovskite absorbing materials like, Cs2TiCl6, Cs2TiBr6, and Cs2TiI6 are examined. Cs2TiBr6 is chosen to be the most promising absorbing layer material alternative suitable for a stable environmentally friendly solar cell application due to its larger spectrum response and tunable band gap than the other promising absorbing materials. The primary objective of this work aims for investigating the functioning of Cs2TiBr6 with various inorganic charge transport materials under simulated conditions using the simulation software, SCAPS-1D (a Solar Cell Capacitance Simulator), Solar Cell Capacitance Simulator, and its functioning is evaluated by varying the interface defect density, thickness, defect density, etc. of various layer materials of the solar cell device. The basic input parameters, like electron-affinity, thickness, band-gap, charge mobility, permittivity, and defect density, of different layer materials are used in the simulation software to accomplish the modelling of the novel structure of solar cell device. A highly efficient environmentally friendly perovskite solar cell structure is the focus of this numerical research. Analysis results are compared with the existing data for substantiation. Finally, one planar inverted, high performance device structure, Glass/MoO3/Cs2TiBr6/SnO2/Au, is evolved, which is a promising eco-friendly device that can be used for making solar panels without any toxic consequences. The short circuit current density, the open circuit voltage, power conversion efficiency, and the fill-factor of this innovative inverted solar cell structure are observed to be 16.589 mA/cm2, 1.1 V, 15.68 %, and 85.76 %, which are significantly better parameters than those previously reported.