Impact of end-group modifications and planarity on BDP-based non-fullerene acceptors for high-performance organic solar cells by using DFT approach

Computational method on highly efficient D-π-A-π-D-based different molecular acceptors for organic solar cells applications and non-linear optical behaviour

Eight molecular structures (BT-A1 to BT-A8) with high-performance non-fullerene acceptor (NFA) were selected for organic solar cells (OSCs) and non-linear optical (NLO) applications. Their electronic, photovoltaic (PV) and optoelectronic properties were tuned by adding powerful electron-withdrawing groups to the acceptor (A) of the D-π-A-π-D structure. Using time-dependent density functional theory (TD-DFT) techniques, based on the laws of quantum chemical calculations, the absorption spectra, stability of the highest and lowest-energy molecular orbitals (HOMO/LUMOs), electron density, intramolecular charge transfer (ICT), transition density matrix (TDM), were examined. The binding energy (Eb) and density of states (DOS) were probed to realize the optoelectronic analysis of the structures BT-A1 to BT-A8. Noncovalent interactions (NCIs) based on a reduced density gradient (RDG) were used to describe the nature and strength of D-A interactions in the molecules BT-A1 to BT-A8. The new refined molecules BT-A1 to BT-A8 exhibited strong absorbance bands between 408-721 nm and high electron transfer contribution (ETC) ranges between 87-96 %, along with the smallest excitation energies (Ex) between 1.71-3.55 eV in the solvent dichloromethane. Dipolar moment strengths ranging from 0.38 to 4.72 Debye in both the excited and ground states have determined with good solubility properties of BT-A1 to BT-A8 in polar solvent. Highly effective charge mobilities and prevention of charge recombination have been demonstrated by the electron (0.18-0.41 eV) and hole RE values (0.13-0.89 eV) for the new compounds. Power conversion efficiencies (PCE) of BT-A1 to BT-A8 were nearly the same because of better outcomes compared to the molecules in the BT. Compared to poly[4.8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b: 4,5-b']dithiophene-2,6- diyl-alt-(4-2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th), the open circuit voltages (Voc) of compounds BT-A1 to BT-A8 were ranged from 1.52 to 2.13 eV. The polarizability (α) and hyperpolarizability (β) of the molecules BT-A1 to BT-A8 were used to determine the non-linear optical (NLO) properties. The results showed that BT-A2, BT-A6 and BT-A7 have good NLO activity. This computational analysis demonstrates the superiority of the molecules with NFA. Hence the compounds are advised for the use in production of high-performance OSCs and NLO activity.

Exploration of the synergistic effect of chrysene-based core and benzothiophene acceptors on photovoltaic properties of organic solar cells

To improve the efficacy of organic solar cells (OSCs), novel small acceptor molecules (CTD1-CTD7) were designed by modification at the terminal acceptors of reference compound CTR. The optoelectronic properties of the investigated compounds (CTD1-CTD7) were accomplished by employing density functional theory (DFT) in combination with time-dependent density functional theory (TD-DFT). The M06 functional along with a 6-311G(d,p) basis set was utilized for calculating various parameters such as: frontier molecular orbitals (FMO), absorption maxima (λmax), binding energy (Eb), transition density matrix (TDM), density of states (DOS), and open circuit voltage (Voc) of entitled chromophores. A red shift in the absorption spectra of all designed chromophores (CTD1-CTD7) was observed as compared to CTR, accompanied by low excitation energy. Particularly, CTD4 was characterized by the highest λmax value of 685.791 nm and the lowest transition energy value of 1.801 eV which might be ascribed to the robust electron-withdrawing end-capped acceptor group. The observed reduced binding energy (Eb) was linked to an elevated rate of exciton dissociation and substantial charge transfer from central core in HOMO towards terminal acceptors in LUMO. These results were further supported by the outcomes from TDM and DOS analyses. Among all entitled chromophores, CTD4 exhibited bathochromic shift (685.791 nm), minimum HOMO/LUMO band gap of 2.347 eV with greater CT. Thus, it can be concluded that by employing molecular engineering with efficient acceptor moieties, the efficiency of photovoltaic materials could be improved.

Designing efficient materials for high-performance of non-fullerene organic solar cells through side-chain engineering on DBT-4F derivatives by non-fused-ring electron acceptors

CONTEXT

For the advancement in fields of organic and perovskite solar cells, various techniques of structural alterations are being employed on previously reported chromophores. In this study, the end-capped engineering is carried out on DBT-4F (R) by modifying terminal acceptors to improve optoelectronic and photovoltaic attributes. Seven molecules (AD1-AD7) are modeled using different push-pull acceptors. DFT/B3LYP/6-31G along with its time-dependent approach (TD-DFT) are on a payroll to investigate ground state geometries, absorption maxima (λmax), energy gap (Eg), excitation energy (Ex), internal reorganization energy, light harvesting efficiency (LHE), dielectric constant, open circuit voltage (VOC), fill factor (FF), etc. of OSCs. AD1 displayed the lowest band gap (1.76 eV), highest λmax (876 nm), lowest Ex (1.41 eV), and lowest binding energy (0.21 eV). Among various calculated parameters, all of the sketched molecules demonstrated greater dielectric constant when compared to R. The highest dielectric constant was exhibited by AD3 (56.26). AD5 exhibited maximum LHE (0.9980). Lower reorganization energies demonstrated improved charge mobility. AD5 and AD7 (1.63 and 1.68 eV) have higher values of VOC than R (1.51 eV). All novel molecules having outperforming attributes will be better candidates to enhance the efficacy of OSCs for future use.

METHODS

Precisely, a DFT and TD-DFT analysis on all of the proposed organic molecules were conducted, using the functional MPW1PW91 at 6-31G (d,p) basis set to examine their optoelectronic aspects, additionally the solvent-state computations were studied with a TD-SCF simulation. For all these simulations, Guassian 09 and GuassView 5.0 were employed. Moreover, the Origin 6.0, Multiwfn 3.8, and PyMOlyze 1.1 software were utilized for the visual depiction of the graphs of absorption, TDM, and DOS, respectively of the studied molecules. A number of crucial aspects such as FMOs, bandgaps, light-harvesting efficiency, electrostatic potential, dipole moment, ionization potential, open-circuit voltage, fill factor, binding energy, interaction coefficient, chemical hardness-softness, and electrophilicity index were also investigated for the studied molecules.

Boosting the Performance of Diketopyrrolopyrrole-Triphenylamine-Based Organic Solar Cells via π-Linker Engineering

The design and development of novel and efficient donor-π-acceptor (D-π-A) type conjugated systems has attracted substantial interest in the field of organic electronics owing to their intriguing properties. In this paper, we have designed seven new and efficient D-π-A type conjugated systems (M1-M7) by a variety of π-linkers with triphenylamine (TPA) as the electron donor and diphenyldiketopyrrolopyrrole (DPP) as the electron acceptor using density functional theory (DFT) formalism for organic solar cells (OSCs). The π-linker has been substituted between the donor and acceptor for efficient electron transfer. Here, our primary focus is on narrowing the highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, electronic transition, charge transfer rate, reorganization energies, and the theoretical power conversion efficiencies (PCEs). Our study reveals that the designed compounds exhibit excellent charge transfer rates. The absorption properties of the compounds have been examined using the time-dependent density functional theory (TD-DFT) method. The TD-DFT study shows that compound M2 possesses the highest absorption maxima with a maximum bathochromic shift. For a better understanding of the electron transport process of our designed compounds, we have designed donor/acceptor (D/A) blends, and each of the developed blends (FREA/M1-M7) can encourage charge carrier separation. According to the photovoltaic performance of the D/A blends, compound FREA-M2, which has a theoretical PCE of 16.53%, is the most appealing choice for use in OSCs. We expect that by thoroughly examining the relationship between structure, characteristics, and performance, this work will serve as a roadmap for future research and development of TPA-DPP-based photovoltaic materials.

Designing Thieno[3,4-c]pyrrole-4,6-dione Core-Based, A2-D-A1-D-A2-Type Acceptor Molecules for Promising Photovoltaic Parameters in Organic Photovoltaic Cells

Nonfullerene-based organic solar cells can be utilized as favorable photovoltaic and optoelectronic devices due to their enhanced life span and efficiency. In this research, seven new molecules were designed to improve the working efficiency of organic solar cells by utilizing a terminal acceptor modification approach. The perceived A2-D-A1-D-A2 configuration-based molecules possess a lower band gap ranging from 1.95 to 2.21 eV compared to the pre-existing reference molecule (RW), which has a band gap of 2.23 eV. The modified molecules also exhibit higher λmax values ranging from 672 to 768 nm in the gaseous and 715-839 nm in solvent phases, respectively, as compared to the (RW) molecule, which has λmax values at 673 and 719 nm in gas and chloroform medium, respectively. The ground state geometries, molecular planarity parameter, and span of deviation from the plane were analyzed to study the planarity of all of the molecules. The natural transition orbitals, the density of state, molecular electrostatic potential, noncovalent interactions, frontier molecular orbitals, and transition density matrix analysis of all studied molecules were executed to validate the optoelectronic properties of these molecules. Improved charge mobilities and dipole moments were observed, as newly designed molecules possessed lower internal reorganization energies. The open circuit voltage (Voc) of W4, W5, W6, and W7 among newly designed molecules was improved as compared to the reference molecule. These results elaborate on the superiority of these novel-designed molecules over the pre-existing (RW) molecule as potential blocks for better organic solar cell applications.

A computational insight into enhancement of photovoltaic properties of non-fullerene acceptors by end-group modulations in the structural framework of INPIC molecule

Improving the open circuit voltage is a major challenge for enhancing the overall efficiency of organic solar cells. Current work has concentrated on improving open-circuit voltage by designing new molecular frameworks from an INPIC molecule having a conjugated fused core. We modulated the structure by changing the terminal groups of the reference molecule (INPIC) with seven strong electron-withdrawing units. We investigated various optoelectronic attributes, charge transfer, and photovoltaic and geometrical parameters by compiling the B3LYP/6-31G(d,p) functional of the DFT approach. The optical absorption for modulated molecules ranges from 748.51 nm to 845.96 nm while showing higher oscillation strength than INPIC. At the same time, their impressive charge transport is attributed to their smaller excitation and exciton binding energy, higher electron/hole mobility, narrower band gap, and a more than 99 % intramolecular charge transfer. The larger dipole moments help in the dense interaction of acceptors with employed donor J61 which, in turn, improves charge transfer at the donor-acceptor interface. One of the triumphs that are difficult to get in organic molecules is success in achieving a higher open circuit voltage (VOC). Our conceptualized molecular frameworks of acceptors are featured with a notable VOC improvement in the range of 1.84-2.05 eV. Thus, the results of the current investigation pave the root for architecting the acceptor molecules with impressive optoelectrical properties that may be capable of providing high photovoltaic output. Thus these acceptors can be utilized for the development of advanced organic solar cells in future.

Effect of Benzothiadiazole-Based π-Spacers on Fine-Tuning of Optoelectronic Properties of Oligothiophene-Core Donor Materials for Efficient Organic Solar Cells: A DFT Study

In this work, five novel A-π-D-π-A type molecules D1-D5 were designed by adding unusual benzothiadiazole derivatives as π-spacer blocks to the efficient reference molecule DRCN5T for application as donor materials in organic solar cells (OSCs). Based on a density functional theory approach, a comprehensive theoretical study was performed with different functionals (B3LYP, B3LYP-GD3, B3LYP-GD3BJ, CAM-B3LYP, M06, M062X, and wB97XD) and with different solvent types (PCM and SMD) at the extended basis set 6-311+g(d,p) to evaluate the structural, optoelectronic, and intramolecular charge transfer properties of these molecules. The B3LYP-GD3BJ hybrid functional was used to optimize the studied molecules in CHCl3 solution with the SMD model solvent as it provided the best results compared to experimental data. Transition density matrix maps were simulated to examine the hole-electron localization and the electronic excitation processes in the excited state, and photovoltaic parameters including open-circuit photovoltage and fill factor were investigated to predict the efficiency of these materials. All the designed materials showed promising optoelectronic and photovoltaic characteristics, and for most of them, a red shift. Out of the proposed molecules, [1,2,5]thiadiazolo[3,4-d]pyridazine was selected as a promising π-spacer block to evaluate its interaction with PC61BM in a composite to understand the charge transfer between the donor and acceptor subparts. Overall, this study showed that adding π-spacer building blocks to the molecular structure is undoubtedly a potential strategy to further enhance the performance of donor materials for OSC applications.

A DFT study for improving the photovoltaic performance of organic solar cells by designing symmetric non-fullerene acceptors by quantum chemical modification on pre-existed LC81 molecule

Minimizing the energy loss and improving the open circuit voltage of organic solar cells is still a primary concern for scientists working in this field. With the aim to enhance the photovoltaic performance of organic solar cells by minimizing energy loss and improving open circuit voltage, seven new acceptor molecules (LC1-LC7) are presented in this work. These molecules are designed by modifying the terminal acceptors of pre-existed "LC81" molecule based on an indacinodithiophene (IDT) fused core. The end-group modification approach is very fruitful in ameliorating the efficacy and optoelectric behavior of OSCs. The newly developed molecules presented remarkable improvements in performance-related parameters and optoelectronic properties. Among all designed molecules, LC7 exhibited the highest absorption maxima (λmax = 869 nm) with the lowest band-gap (1.79 eV), lowest excitation energy (Ex = 1.42 eV), lowest binding energy, and highest excited state lifetime (0.41 ns). The newly designed molecules LC2, LC3, and LC4 exhibited remarkably improved Voc that was 1.84 eV, 1.82 eV, and 1.79 eV accordingly, compared to the LC81 molecule with Voc of 1.74 eV LC2 molecule showed significant improvement in fill factor compared to the previously presented LC81 molecule. LC2, LC6, and LC7 showed a remarkable reduction in energy loss by showing Eloss values of 0.26 eV, 0.18 eV, and 0.25 eV than LC81 molecule (0.37 eV). These findings validate the supremacy of these developed molecules (especially LC2) as potential components of future OSCs.

Exploration of charge transfer analysis and photovoltaics properties of A-D-A type non-fullerene phenazine based molecules to enhance the organic solar cell properties

To intensify the photovoltaic properties of organic solar cells, density functional theory (DFT) based computational techniques were implemented on six non-fullerene A-D-A type small molecules (N1-N6) modified from reference molecule (R) which consists of phenazine fused with 1,4- Dimethyl-4H-3,7-dithia-4-aza- cyclopenta [α] pentalene on both sides with one of its phenyl rings acting as the central donor unit, further attached with 2-(5,6-Difluoro-2-methylene-3-oxo-indan-1-ylidene)-malononitrile acceptor groups at terminal sites. All proposed compounds have a phenazine base modified with a variety of substituents at the terminals. Transition density matrix, density of states, frontier molecular orbitals, intramolecular charge transfer abilities and optoelectronic properties of these compounds were investigated using B3LYP/6-31G (d, p) and B3LYP/6-31G++ (d,p) level of theory. All six designed compounds exhibited a bathochromic sift in their λmax as compared to the R molecule. All designed molecules also have reduced band gap and smaller excitation energy than R. Among all, N6 exhibited highest λmax and lowest bandgap as compared to reference molecule indicating its promising photovoltaic properties. Decreased hole and electron reorganization energy in several of the suggested compounds is indicative of greater charge mobility in them. PTB7-Th donor was employed to calculate open circuit voltage of all investigated molecules. N1-N5 molecules had improved optoelectronic properties, significant probable power conversion efficiency as evident from their absorption aspects, high values of Voc, and fill factor, compared to R molecule. Designed A-D-A type NF based molecules make OSCs ideal for use in wearable devices, building-integrated photovoltaics and smart fabrics.

End-cap modeling on the thienyl-substituted benzodithiophene trimer-based donor molecule for achieving higher photovoltaic performance

Despite the substantial advancements in organic solar cells (OSCs), the best devices still have quite low efficiencies due to less focus on donor molecules. With the intention to present efficient donor materials, seven small donor molecules (T1-T7) were devised from DRTB-T molecule by using end-capped modeling. Newly designed molecules exhibited remarkable improved optoelectronic properties such as less band gap (from 2.00 to 2.23 eV) than DRTB-T having band gap of 2.57 eV. Similarly, a significant improvement in λmax values was noticed in designed molecules in gaseous medium (666 nm-738 nm) and solvent medium (691 nm-776 nm) than DRTB-T having λmax values at 568 nm and 588 nm in gas and solvent phase respectively. Among all molecules, T1 and T3 exhibited significant improvement in optoelectronic properties such as narrow band gap, lower excitation energy, higher λmax values and lower electron reorganization energy as compared to pre-existed DRTB-T molecule. The better functional ability of T1-T7 is also suggested by an improvement in open circuit voltage (Voc) of designed structures (1.62 eV-1.77 eV) as compared to R (1.49 eV) when PC61BM is used as an acceptor. So, all our newly derived donors can be employed in the active layer of organic solar cells to manufacture efficient OSCs.

Amplifying the photovoltaic properties of phenylene dithiophene core based non-fused ring by engineering the terminal acceptors modification to enhance the efficiency of organic solar cells

In this study, a series of eight non-fused rings-based semiconducting acceptors (AR1-AR8) were computationally developed by making modifications to the parent molecule (PTICO). In this study, a DFT analysis was conducted at an accurately chosen level of theory to gather a comprehensive inventory of the optoelectronic characteristics of AR1-AR8 and PTICO. The findings indicate that all recently developed molecules exhibit a bathochromic shift in their maximum UV-visible absorbance (λmax) with a smaller band gap (Eg). AR1 has demonstrated the most significant red shift in UV-visible absorbance and possesses the smallest Eg when compared to other recently developed acceptors. AR2 acceptor has shown the best results both as electron and hole-transporting materials owing to its smallest value of reorganization energy for electrons and holes. J61 donor was engaged to calculate the open-circuit voltage (VOC) and the highest VOC with maximum FF % value was observed in AR4. The investigation of charge transfer was also conducted utilizing J61 in conjunction with the AR4 acceptor. Natural transition orbitals (NTO) have also been inspected to recognize the percentage electron transport contribution (% ETC) from the ground state to the first excites state (S0 to S1). The findings of this research suggest that the modified acceptors exhibit potential for practical implementation in the development of organic solar cells that possess improved photovoltaic performance.

DFT study of UV-vis-properties of thiophene-containing Cu(β-diketonato)2 - Application for DSSC

Experimental and theoretically calculated UV-vis properties of three Cu(β-diketonato)₂ complexes are presented. The Cu(β-diketonato)₂ contains β-diketones without (β-diketone = acetylacetone, (CH₃)COCH₂CO(CH₃), complex (1)), with one (β-diketone = thenoyltrifluoroacetone, (CF₃)COCH₂CO(C₄H₃S), complex (2)) and with two thiophene (β-diketone = (CF₃)COCH₂CO(C₄H₂S) (C₄H₃S), complex (3)) groups. More thiophenes on the β-diketonato ligand of Cu(β-diketonato)₂, lead to a red shift of the experimental absorbance maxima of the UV-vis of the complex, from 295 nm for complex (1), to 340 nm for complex (2) to 390 nm for complex (3). Theoretical time dependant density functional theory calculations indicate that both the two strongest absorbance peaks of the ultraviolet-visible spectrum of Cu(acetylacetonato)₂ are mainly ligand-to-metal charge-transfer excitations. However, the absorbance maxima of the UV-vis of thiophene-containing Cu(β-diketonato)₂ are mainly ligand-to-ligand charge-transfer excitations. Calculated properties such as light harvesting energy (LHE = 0.47, 0.94 and 0.99 for (1)-(3) respectively), driving force for electron injection (ΔG_inject = 1.43, 0.76 and 0.63 for (1)-(3) respectively), and driving force of dye regeneration (ΔG_regenerate = 1.85, 2.16 and 1.49 for (1)-(3) respectively), are favourable for (1)-(3) to be considered as dyes in DSSCs. However, some structural modifications are needed to prevent intramolecular charge recombination after excitation.