Hole Reorganization Energies Research Articles

Designing of silolothiophene-linked triphenylamine-based hole transporting materials for perovskites and donors for organic solar cells-A DFT study

Si-OMeTPA is receiving a lot of interest as potential hole transport materials in perovskite solar cells (PSCs) because of their wide range of energy tuning, strong absorption capacity, and excellent power conversion efficiency (PCE). This work includes eight new donors (PEH1-PEH8) containing 4,4-diphenyl-4H-silolo[3,2-b:4,5-b']dithiophene as the central-core unit has been effectively developed and then theoretically described to probe their electronic and optical performance. These innovative (PEH1-PEH8) materials had lower Eg and more significant extinction coefficients, implying superior phase inversion geometry during sandwich structures. The complete theoretical characterization of these proposed (PEH1-PEH8) and reference (PEH) molecules has been achieved by using quantum chemistry techniques. Density functional theory (DFT) and time-dependent (TD-DFT) computations have explored the photo-physical and optoelectronic properties. The density of states (DOS), optical properties, open-circuit voltage, transition density matrix (TDM), Frontier molecular orbital (FMO) alignment, and hole and electron reorganization energies have all been studied for these materials. PEH8 has an excellent absorbance (λmax) of 699.65 nm and an optical band gap of 0.91 eV. Furthermore, a comprehensive investigation of PEH8/PC61BM has shown the fantastic charge shifting at the donor-acceptor interface. As a result, our suggested strategy is required for developing suitable photovoltaic molecules for proficient PSCs that can be employed as light harvesters and electron and hole transporter.

Modulating the strength of acceptor in D-A-D type hole transport materials for efficient inverted perovskite solar cells

We report herein a design strategy to improve the hole mobility of D-A-D-based hole transport material (HTM) by modifying the accepting core of the reference HTMs based on triphenylamine (TPA) and bithieno thiophene (BTTI) units. Eight HTMs are designed by replacing the BTTI unit in BTTI-TPA HTM with several commonly available diones and imides as acceptors. The structural, electronic, optical, and charge transport properties are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The designed molecules are extensively examined for their structural, electronic, and absorption properties to extract the features that improve their hole mobility using the MPW1PW91/6–31 g(d,p) method. We identified four carefully designed BTTD-TPA, DBTT-TPA, NDTTI-TPA, and NDTI-TPA molecules as the most promising HTMs. This work exemplifies the role of the methyl group on electron acceptors on hole reorganization energies. Results obtained from this study provide valuable guidelines for designing efficient HTMs.

Benzodithiophene (BDT) and benzodiselenophene (BDSe) isomers’ charge transport properties for organic optoelectronic devices

This study's primary objective is to give a thorough examination of the comparative charge transport and optoelectronic characteristics of all conceivable isomers of benzodithiophene (BDT) and benzodiselenophene (BDSe). Density Functional Theory (DFT) simulations have been performed on all the possible isomers of benzodithiophene (BDT) and benzodiselenophene (BDSe) and results are compared with corresponding experimental known isomers. The absorption energies and HOMO–LUMO energy levels were predicted by Time-Dependent Density Functional Theory (TD–DFT). Electron and hole Reorganization Energies (RE), Hole Extraction Potential (HEP) and Electron Extraction Potential (EEP), Ionization Potentials (IP) and Electron Affinities (EA) of all the isomers are reported. The UV–visible absorption of BDT and BDSe isomers are between 250–417 nm and 290–445 nm respectively. Comparatively, the simulated hole and electron reorganization energy of all the BDT and BDSe isomers have low values and hence expected applications in the field of Organic Optoelectronic Devices.

Optoelectronic properties of Portulacaxanthin III (PXIII), GQD/Os-GQD-PXIII nanocomposites, and their coupling with photoanode in dye-sensitized solar cells: Molecular and periodic DFT calculations

In this work, the optoelectronic properties of a naturally occurring dye, Portulacaxanthin III (PXIII), were investigated. To improve the performance of PXIII dye, it was hybridized with graphene quantum dot (GQD) undoped and doped with Os at the central position to form two nanocomposites (PXIII-GQD and Os-GQD-PXIII), and their optoelectronic properties were also investigated. Parameters such as frontier molecular orbital energies and distributions, absorption and emission properties, excited-state lifetimes, and hole and electron reorganization energies were calculated at two molecular (HCTH and CAM-B3LYP) DFT functionals and their counterparts TDDFT functionals in the gas phase and with the PCM model to mimic the effect of the solvent in three solvents: chloroform, acetonitrile, and water. The variation of the abovementioned molecular parameters as a function of media polarities (dielectric constants) was investigated. In addition, the coupling with the photoanode TiO2 anatase (101) with a periodic DFT functional was also investigated. The output from this work demonstrated the better overall performance of the nanocomposites (doped and undoped). Since they have better energy level alignments, red-shifted and broader absorption in the Vis and IR regions, better HOMO and LUMO charge separation, and stronger adsorption on the photoanode.

Theoretical Investigation of the Nonlinear Optical and Charge Transport Properties of N-(4-Methoxybenzylidene) Isonicotinohydrazone and Some of Its Derivatives: A DFT and TD-DFT Study

Here, we report the findings from a study on the charge transport and nonlinear optical (NLO) properties of N-(4-methoxybenzylidene) isonicotinohydrazone (INH) and some of its derivatives named INH1-INH15. The density functional theory (DFT) approach was used for ground state computations at the B3LYP-D/6-311G (d,p) level of theory, while the time-dependent density functional theory (TD-DFT) was carried out at the CAM-B3LYP/6-311G (d,p) level. The results show that the energy gaps of all the studied compounds range from 3.933 to 4.645 eV. INH3 and INH4 have the lowest electron and hole reorganization energies (i.e., 0.409 and 0.634 eV, respectively) and can thus be classified as moderate electron and hole-carrying materials for organic light-emitting diode (OLED) applications. TD-DFT computations demonstrate that an extension of the conjugation (in INH2 and INH3) increases the oscillator strength, improving the NLO response. According to the NLO data, INH2 and INH3 have higher static isotropic polarizabilities (38.509 and 37.986 × 10−24 esu, respectively) and second hyperpolarizabilities (54.440 and 57.598 × 10−36 esu, respectively), while INH4 and INH13 have higher first hyperpolarizability values (11.944 and 10.939 × 10−30 esu, respectively). The results reveal that INH derivatives with different groups are viable alternatives for OLED and NLO applications.

Graphene quantum dots (GQD) and edge-functionalized GQDs as hole transport materials in perovskite solar cells for producing renewable energy: a DFT and TD-DFT study.

This study investigated the potential suitability of graphene quantum dots (GQD) and certain edge-functionalized GQDs (GQD-3Xs) as hole transport materials (HTMs) in perovskite solar cells (PSCs). The criteria for appropriate HTMs were evaluated, including solubility, hole mobility, light harvesting efficiency (LHE), exciton binding energy (Eb), hole reorganization energy (λh), hole mobility, and HTM performance. It was found that several of the compounds had higher hole mobility than Spiro-OMeTAD, a commonly used HTM in PSCs. The open circuit voltage and fill factor of the suitable GQD and GQD-3Xs were found to be within appropriate ranges for HTM performance in MAPbI3 PSCs. GQD-COOH and GQD-COOCH3 were identified as the most suitable HTMs due to their high solubility, small λh, and appropriate performance.

Modifying a D-A-π-A-D HTM system for higher hole mobility by the meta-substitution strategy to weaken the electron-donating ability of the donor unit: a DFT study.

Tuning the electron-donating ability (EDA) of the donor units of hole transporting materials (HTMs) is an efficient strategy to modulate the optoelectronic properties of HTMs. Based on this strategy, we first theoretically investigated the effects of the EDA of donor units on D-A-π-A-D architectural HTMs. The results show that the enhanced EDA of the donor unit leads to larger hole reorganization energy and poorer molecular stability of HTMs. In contrast, meta-substitution of side groups is an effective strategy to reduce the EDA of the donor unit. We found that the application of the meta-substitution strategy in the D-A-π-A-D system not only successfully improves the molecular stability, but also achieves higher hole mobility by promoting the electronic coupling between the molecular dimers and decreasing the hole reorganization energies simultaneously. Studies on interfacial properties indicate that intermolecular coupling also synergistically enhances the interfacial charge extraction performance and reduces carrier recombination. In conclusion, by utilizing the meta-substitution strategy to reduce the EDA of donor units on D-A-π-A-D architectural HTMs, we successfully designed four superior performance HTMs mD1, mD2, mD3, and mD4.

Optoelectronic design and charge transport properties of Benzodifuran (BDF) isomers for organic electronic devices: DFT/TD-DFT insights

The primary goal of this work is to provide a comprehensive analysis of the charge transport and optoelectronic characteristics of all the isomers of benzodifuran (BDF) for organic electronic devices in order to suggest qualified materials/candidates for organic photovoltaic devices. Density functional theory (DFT) calculations were performed for all possible isomers of BDF and results are compared with corresponding experimental known isomers. Time Dependent-Density Functional Theory (TD-DFT) is used for the calculation of the absorption and HOMO-LUMO energy levels. To characterize the electronic charge transport state in these isomers, the ionization potentials (IP), reorganization energies (hole and electron), and electron affinities (EA) of all the isomers are investigated. Comparatively, all the BDF isomers are having low electron and hole reorganization energies and hence they can be used in the organic electronic material fabrication.

A computational study of thiophene containing small-molecule electron acceptors for non-fullerene organic photovoltaic cells

During the past few years, researchers have devoted extensive efforts to improve organic solar cell (OSC) performance to reach interesting power conversion efficiencies (PCE) exceeding 10 %. Among heterojunctions OSCs (BHJ) types, Fullerene based small molecule acceptors (SMAs) have proved to be a favorable option in virtue of their high-power conversion efficiency (PCE), good electronic conductivity and superior charge segregation. Yet, they represent some serious limitations, such as low light absorption over 600 nm, solubility in organic solvents, and inefficient processing. Accordingly, the so-called non-fullerene acceptors (NFA) organic group was developed and showed excellent characteristics over fullerene acceptors with their easily tunable band gap, strong absorption in the visible region, low voltage loss, good morphological stability and simple fabrication techniques. In the present paper, a series of non-fullerene electron acceptors (C1–C4) were designed by modifying the reference material R. we have obtained new conjugated organic structures by adding more functional capped units. The quantum chemical study (DFT/TD-DFT) approach was used to perform theoretical calculations in order to characterize the effect of end group redistribution via the frontier molecular orbital (FMO), optical absorption, reorganization energy in accordance with R. Using PTB7-Th as an electron donor, open circuit voltage (Voc), photovoltaic properties and intermolecular charge transfer have been also calculated for all the conceived compounds. The findings revealed that all engineered materials (C1–C4) possess narrow band gap and great optical characteristics. In addition the proposed structures have displayed comparatively lower electron and hole reorganization energies, we have found that C1 represents the lowest electron and hole reorganization energies, respectively 0.048 eV and 0.028 eV, consequently the highest electron and hole mobility [1]. These interesting outcomes could prove proposed electron acceptors to be excellent candidates in the improvement of optoelectronic properties of organic solar cell technology.

Tuning the Electronic and Charge Transport Properties of Schiff Base Compounds by Electron Donor and/or Acceptor Groups

Organic semiconductors have gained substantial interest as active materials in electronic devices due to their advantages over conventional semiconductors. We first designed four Schiff base compounds, then the effect of electron donor/acceptor groups (methyl/nitro) was studied on the compounds' electronic and transport nature. The absorption spectra (λabs) were computed by time-dependent DFT at TD-B3LYP/6-31+G** level. The effect of different solvents (ethanol, DMF, DMSO, and acetone) was investigated on the λabs. The substitution of the -NO2 group to the furan moiety at the 5th position in Compound 3 leads to a red-shift in the absorption spectrum. A smaller hole reorganization energy value in Compound 3 would be beneficial to get the hole's intrinsic mobility. In contrast, a reduced-electron reorganization energy value of Compound 4 than hole may result in enhanced electron charge transfer capabilities. The reorganization energies of compounds 1 and 2 exposed balanced hole/electron transport probability. The optical, electronic, and charge transport properties at the molecular level indicate that Compound 3 is suitable for organic electronic device applications.

Thiophene-based molecules as hole transport materials for efficient perovskite solar cells or as donors for organic solar cells

This study focuses on optoelectronic features of a series of D-A-D molecules composed of thiophene, ethylenedioxythiophene, or 3,4-dimethoxythiophene acceptor groups substituted in several positions using different end-capped electron-donating groups formed from triphenylamine or OMe-triphenylamine. The influence of π-extension on the charge transfer process is probed by inserting two azomethine groups between acceptor and donor (D-π-A-π-D) groups to make them economically profitable like solar cells. The experimental results available in the literature are combined with our detailed B3LYP/6-311G(d,p) study to find relationships between the structural, and optoelectronic properties of molecules and their performance as HTMs or as donors in organic photovoltaic cells. All investigated molecules were preferential competitors for HTMs in perovskite solar cells because of their excellent HOMO delocalization, lower hole reorganization energies, and high light-harvesting efficiency. They all show a spontaneous solvation process within dichloromethane and have larger Stokes shifts with respect to that of spiro-OMeTAD, which is advantageous for the pore-filling of HTMs for PSCs. The bound electron-hole pairs of the studied molecules can easily escape coulomb attraction by dissociating into negative and positive charges, thus facilitating hole transport, and improving the short-circuit current density. D-A-D type molecules have a blue-shifted absorption maximum in the visible light region and consequently have no overlap with the light-harvesting of the perovskite layer. The π-bridges lengthen the electronic conjugation path of the D-π-A-π-D compounds and introduce more flexibility to the molecule's backbone. Their higher radiative lifetimes make them good candidates for their usage in organic solar cell applications.

DFT molecular modeling of A2-D-A1-D-A2 type DF-PCIC based small molecules acceptors for organic photovoltaic cells

In this study, five new compounds of A2-D-A1-D-A2 type were developed from DF-PCIC (R) molecule, to enhance the photo-voltaic efficiency of organic photovoltaic (OPV) devices. The density functional theory calculations of the proposed acceptors were executed using MPW1PW91 in combination with 6-31G(d,p), while its time-dependent (TD-DFT) approach was employed for the calculations of the excited-state. A wide range of geometric metrics including density of state, binding energy, electrostatic potential, dipole moment, transition density matrix, and device performance were predicted in accordance with R molecule. With the donor molecule PTB7-Th, theoretical VOC, the normalized VOC as well as the fill factor of all investigated acceptors were also calculated. The findings from these analyses showed that most of our proposed compounds (PCIC1-PCIC5) could prove themselves to be paramount candidates for enhanced opto-electronic properties in an OPV cell because of their red-shifted absorption maximum in chloroform, as well as in gas phase, narrow bandgap, lower excitation energy, higher dipole moment, and comparably lower binding energies, etc. Furthermore, the lowest electron reorganization energy (0.089880 eV) of PCIC2, and the hole reorganization energy (0.171867 eV) of PCIC1, represented their highest electron and hole mobility, respectively, amongst all. Overall, we could say that all proposed chromophores had computationally preferred metrics, indicating that they could be used in the improvement of solar cell technology in the course of time.

Investigating the Role of Novel Benzotrithiophene-Based Bat-Shaped Non-Fullerene Acceptors for High Performance Organic Solar Cells

The development of an effective building blocks considered the boon in constructing highly efficient nonfullerene electron acceptors (NFEAs). The first theoretical design and investigation of environmental-friendly groups for changing potential end-capped electron acceptor molecules for high-performance environmental-friendly OSCs is proposed in this study. We developed BTT-based [Formula: see text]–[Formula: see text]–[Formula: see text]–[Formula: see text]–[Formula: see text] (acceptor–bridge–core–bridge–acceptor) type, neoteric Bat-shaped environmental-friendly acceptor molecules (K1–K6) for the first time by replacing the electronegative –F group of BTT with four electron-withdrawing (–CN, –COOCH3, –NO2, –Cl) groups. K1–K6 has its exciton-binding energy ([Formula: see text]), open-circuit voltage ([Formula: see text]), frontier molecular orbital analysis (FMO), transition density matrix (TDM) analysis, electron and hole reorganization energy ([Formula: see text]e, [Formula: see text]h), density of state (DOS) graphs, and transition energy Ex values computed and compared to the recently proposed high-performance BTT molecule. According to the research, the photovoltaic, photo-physical and electrical applications of proposed molecules K1–K6 are comparable to those of [Formula: see text]. When compared to reference [Formula: see text] and proposed molecules, K6 tested to be the proverbial optoelectronic compound for OSCs due to its low [Formula: see text] (2.05[Formula: see text]eV), lowest [Formula: see text] (1.57[Formula: see text]eV), highest [Formula: see text] max values of 790.61[Formula: see text]nm in CHCl3, 0.95[Formula: see text]V value for [Formula: see text] and comparable [Formula: see text] (0.482[Formula: see text]eV). The superposition of orbitals and lucrative charge shift from the highest occupied molecular orbital (HOMO) (PTB7-Th) to the lowest unoccupied molecular orbital (LUMO) were verified by charge transfer study among the K6: PTB7-Th combine. As a result, the proposed molecules (K1–K6) with exceptional optoelectronic capabilities are suggested as the best harmless alternative materials for creating proficient and environmental-friendly OSCs.

Design of Molecules with Low Hole and Electron Reorganization Energy Using DFT Calculations and Bayesian Optimization.

Materials exhibiting higher mobility than conventional organic semiconducting materials, such as fullerenes and fused thiophenes, are in high demand for applications in printed electronics. To discover new molecules that might show improved charge mobility, the adaptive design of experiments (DoE) to design molecules with low reorganization energy was performed by combining density functional theory (DFT) methods and machine learning techniques. DFT-calculated values of 165 molecules were used as an initial training dataset for a Gaussian process regression (GPR) model, and five rounds of molecular designs applying the GPR model and validation via DFT calculations were executed. As a result, new molecules whose reorganization energy is smaller than the lowest value in the initial training dataset were successfully discovered.

De Novo Design of Molecules with Low Hole Reorganization Energy Based on a Quarter-Million Molecule DFT Screen: Part 2.

Organic semiconductors have many desirable properties including improved manufacturing and flexible mechanical properties. Due to the vastness of chemical space, it is essential to efficiently explore chemical space when designing new materials, including through the use of generative techniques. New generative machine learning methods for molecular design continue to be published in the literature at a significant rate but successfully adapting methods to new chemistry and problem domains remains difficult. These challenges necessitate continual method evaluation to probe method viability for use in alternative applications not covered in the original works. In continuation of our previous work, we evaluate four additional machine-learning-based de novo methods for generating molecules with high predicted hole mobility for use in semiconductor applications. The four generative methods evaluated here are (1) Molecule Deep Q-Networks (MolDQN), which utilizes Deep-Q learning to directly optimize molecular structure graphs for desired properties instead of generating SMILES, (2) Graph-based Genetic Algorithm (GraphGA), which uses a genetic algorithm for optimization where crossovers and mutations are defined in terms of RDKit's reaction SMILES, (3) Generative Tensorial Reinforcement Learning (GENTRL), which is a variational autoencoder (VAE) with a learned prior distribution and optimized using reinforcement learning, and (4) Monte Carlo tree search exploration of chemical space in conjunction with a recurrent neural network (RNN) decoder (ChemTS). The generated molecules were evaluated using density functional theory (DFT) and we discovered better performing molecules with the GraphGA method compared to the other approaches.

Theoretical study on photophysical properties of twisted D-A interaction TPA-BSM derivatives

Luminogens with aggregation-induced emission (AIE) properties have received considerable attention as excellent candidates for optoelectronics, chemical/biosensors, and bioimaging. Recently, molecule TPA-BSM with the twisted intramolecular charge transfer, with a twist angle of 40.96° between the donor TPA and acceptor BSM units, has exhibited unique photophysical properties, especially the AIE properties in the aggregate and solid state. However, the relationship between their structure and performance has not been fully explored, which will further expand their application areas. Herein, based on the reported TPA-BSM, four new derivatives are designed. Their electronic structure, electron absorption, hole reorganization energy and second-order NLO response have been systematically studied using DFT and TD-DFT theories. It is found that they are all narrow bandgap derivatives. The introduction of donor units can reduce the energy gap, red-shift the first absorption peak, increase the dipole moment and the static first hyperpolarizability, while the introduction of acceptor units is just the opposite. However, the introduction of donor or acceptor units cannot further enhance the hole transport performance, but except for molecule TB-N(CH3)2, the other four derivatives are potential hole transport materials. Due to have large first hyperpolarizabilities of the investigated derivatives, they are promising candidates for excellent second-order NLO materials.

Structural modification on Dimethoxythienothiophene based non-fullerene acceptor molecule for construction of high-performance organic chromophores by employing DFT approach

In this work, with the directive of increasing the power conversion efficiency of organic solar cells, seven new acceptor molecules (N1–N7) have been designed by the end-group modification of A-D-A type reference molecule TTDTC-4F (R). Density functional theory (DFT) based computational methodologies were applied to these structures to calculate different parameters like their planarity, bandgaps, maximum absorption wavelengths, excitation energies, oscillator strengths, light-harvesting efficiencies, electron and hole reorganization energies, binding energies, dipole moments, open-circuit voltage (Voc), and fill factors (FF), etc. All the devised structures showed better results in terms of their shorter bandgaps, redshift in absorption, lower excitation and binding energies, along with reduced reorganization energies, which emphasizes their better charge transfer properties with respect to R. Furthermore, they also demonstrated good values of dipole moment and light-harvesting efficiencies (LHE). Higher LHE values of designed molecules pointed towards their better abilities to harvest light in order to produce charge carriers. But in terms of open-circuit voltage (Voc) and fill factor (FF), N2 and N5 showed higher, while N7 showed the highest result when compared to R. So, these developed molecules could be the best choice for utilization in the active layer of organic solar cells (OSCs).

Medium Diradical Character, Small Hole and Electron Reorganization Energies and Ambipolar Transistors in Difluorenoheteroles

Four difluorenoheteroles having a central quinoidal core with the heteroring varying as furan, thiophene, its dioxide derivative and pyrrole have shown to be medium character diradicals. Solid-state structures, optical, photophysical, magnetic, and electrochemical properties have been discussed in terms of diradical character, variation of aromatic character and captodative effects (electron affinity). Organic field-effect transistors (OFETs) have been prepared, showing balanced hole and electron mobilities of the order of 10−3 cm2 V−1 s−1 or ambipolar charge transport which is first inferred from their redox amphoterism. Quantum chemical calculations show that the electrical behavior is originated from the medium diradical character which produces similar reorganization energies for hole and electron transports. The vision of a diradical as simultaneously bearing pseudo-hole and pseudo-electron defects might justify the reduced values of reorganization energies for both regimes. Structure-function relationships between diradical and ambipolar electrical behavior are revealed.

Medium Diradical Character, Small Hole and Electron Reorganization Energies and Ambipolar Transistors in Difluorenoheteroles.

Four difluorenoheteroles having a central quinoidal core with the heteroring varying as furan, thiophene, its dioxide derivative and pyrrole have shown to be medium character diradicals. Solid‐state structures, optical, photophysical, magnetic, and electrochemical properties have been discussed in terms of diradical character, variation of aromatic character and captodative effects (electron affinity). Organic field‐effect transistors (OFETs) have been prepared, showing balanced hole and electron mobilities of the order of 10−3 cm2 V−1 s−1 or ambipolar charge transport which is first inferred from their redox amphoterism. Quantum chemical calculations show that the electrical behavior is originated from the medium diradical character which produces similar reorganization energies for hole and electron transports. The vision of a diradical as simultaneously bearing pseudo‐hole and pseudo‐electron defects might justify the reduced values of reorganization energies for both regimes. Structure‐function relationships between diradical and ambipolar electrical behavior are revealed.

Light-Emitting Properties of Pyrimidine-5-Carbonitrile Derivatives: a Theoretical Calculation

In this study, 4,6-Di (9H-carbazol-9-yl) pyrimidine-5-carbonitrile (C1), 4,6-bis (3,6-di-tert-butyl-9H-carbazol-9-yl) pyrimidine-5-carbonitrile (C2), 4,6-bis (3,6-dimethoxy-9H-carbazol-9-yl) pyrimidine-5-carbonitrile (C3) compounds were optimized at the B3LYP/6-31G(d) level. Energy densities of frontier molecular orbitals were investigated with molecular properties. Vertical ionization potentials (IPv), adiabatic ionization potential (IPa) (in eV), vertical electron affinity (EAv), adiabatic electron affinity (EAa), the hole reorganization energy (h )and electron reorganization energy (e ) were calculated (in eV) for C1, C2 and C3 compounds. e values of the C1 and C3 compounds are 0.29 and 0.30 eV and the h value is 0.18 and 0.20 eV, respectively. It can be said that the C1 and C3 compounds are not suitable as an electron bearing layers (ETL) material since its e values are greater than 0.276 eV and that its h value is less than 0.290 eV, so they are a suitable material for the hole bearing layers (HTL). The C2 compound is suitable for both ETL and HTL materials.