Exploring the Electronic, Optical, and Charge Transfer Properties of A-D-A-Type IDTV-ThIC-Based Molecules To Enhance Photovoltaic Performance of Organic Solar Cells

Improving the charge mobility and optoelectronic properties of indacenodithiophene-based small molecule acceptors is a key challenge to improving overall efficiency. In this current research, seven newly designed molecules (DT1-DT7) comprising the indacenodithiophene-based core are presented to tune energy levels, enhance charge mobility, and improve the photovoltaic performance of IDTV-ThIC molecules via density functional theory. All the molecules were designed by end-capped modification by substituting terminal acceptors of IDTV-ThIC with strong electron-withdrawing moieties. Among all the examined structures, DT1 has proved itself a superior molecule in multiple aspects, including higher λmax in chloroform (787 nm) and gaseous phase (727 nm), narrow band gap (2.16 eV), higher electron affinity (3.31 eV), least excitation energy (1.57 eV), and improved charge mobility due to low reorganization energy and higher excited state lifetime (2.37 ns) when compared to the reference (IDTV-ThIC) and other molecules. DT5 also showed remarkable improvement in different parameters, such as the lowest exciton binding energy (0.41 eV), leading to easier charge moveability. The improved open-circuit voltage of DT4 and DT5 makes them proficient molecules exhibiting the charge transfer phenomenon. The enlightened outcomes of these molecules can pave a new route to develop efficient organic solar cell devices using these molecules, especially DT1, DT4, and DT5.

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.

Synthesis and Characterization of Novel Thienothiadiazole-Based D-π-A-π-D Fluorophores as Potential NIR Imaging Agents

As fluorescence bioimaging has increased in popularity, there have been numerous reports on designing organic fluorophores with desirable properties amenable to perform this task, specifically fluorophores with emission in the near-infrared II (NIR-II) region. One such strategy is to utilize the donor-π-acceptor-π-donor approach (D-π-A-π-D), as this allows for control of the photophysical properties of the resulting fluorophores through modulation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Herein, we illustrate the properties of thienothiadiazole (TTD) as an effective acceptor moiety in the design of NIR emissive fluorophores. TTD is a well-known electron-deficient species, but its use as an acceptor in D-π-A-π-D systems has not been extensively studied. We employed TTD as an acceptor unit in a series of two fluorophores and characterized the photophysical properties through experimental and computational studies. Both fluorophores exhibited emission maxima in the NIR-I that extends into the NIR-II. We also utilized electron paramagnetic resonance (EPR) spectroscopy to rationalize differences in the measured quantum yield values and demonstrated, to our knowledge, the first experimental evidence of radical species on a TTD-based small-molecule fluorophore. Encapsulation of the fluorophores using a surfactant formed polymeric nanoparticles, which were studied by photophysical and morphological techniques. The results of this work illustrate the potential of TTD as an acceptor in the design of NIR-II emissive fluorophores for fluorescence bioimaging applications.

Quantum Modification of Indacenodithieno[3,2-b]thiophene-Based Non-fullerene Acceptor Molecules for Organic Solar Cells of High Efficiency

In order to enhance the efficacy of organic solar cells, six new three-dimensional small donor molecules (IT-SM1 to IT-SM6) have been computationally designed by modifying the peripheral acceptors of the reference molecule (IT-SMR). The frontier molecular orbitals revealed that IT-SM2 to IT-SM5 had a smaller band gap (E_gap) than IT-SMR. They also had smaller excitation energies (E_x) and exhibited a bathochromic shift in their absorption maxima (λ_max) when compared to IT-SMR. In both the gas and chloroform phases, IT-SM2 had the largest dipole moment. IT-SM2 also had the best electron mobility, while IT-SM6 had the best hole mobility owing to their smallest reorganization energy for electron (0.1127 eV) and hole (0.0907 eV) mobility, respectively. The analyzed donor molecules' open-circuit voltage (V_OC) indicated that all of these proposed molecules had greater V_OC and fill factor (FF) values than the IT-SMR molecule. In accordance with the evidence of this work, the altered molecules can seem to be quite proficient for usage by experimentalists and have prospective use in future in the manufacture of organic solar cells with improved photovoltaic properties.

Tuning the optoelectronic properties of acridine-triphenylamine (ACR-TPA) based novel hole transporting material for high efficiency perovskite and organic solar cell

In this research, five distinct small donor molecules (designated as ACR-TPA-X1, ACR-TPA-X2, ACR-TPA-X3, ACR-TPA-X4, ACR-TPA-X5) are constructed by replacing the methoxy groups on both sides of the model molecule (ACR-TPA-R) with thiophene bridged acceptor moieties. We have used the B3LYP/6-31G (d,p) model for our computational studies. Our model molecule's morphological alteration has resulted in a lowered E_g of 1.77-2.51 eV as compared to model (ACR-TPA-R=3.84 eV). ACR-TPA-X2 investigated the λ_max at 776 nm. ACR-TPA-X4 was found to be most miscible with dichloromethane (DCM). The greatest V_OC(1.21 eV) was observed in ACR-TPA-X1. Among all of the variants, ACR-TPA-X1 had the highest PCE (23.42%). It was found that ACR-TPA-X4 had the highest electron mobility (0.00370 eV) and ACR-TPA-X5 had the highest hole mobility (0.00324 eV) of all the materials examined. The findings prove the worth of the methods used, paving the way for the development of effective small donors for OSCs and HTMs for PSCs.

4,7-Bis(5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine

Donor molecules of the D-π-A-π-D type structure are often used for applications in organic photovoltaics. In this communication, bromination of 4,7-di(thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine followed by Suzuki cross-coupling with carbazoleboronic acid gave 4,7-bis( 5-(9-hexyl-9H-carbazol-3-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-d]pyridazine. The structure of the newly synthesized compounds was established by high resolution mass-spectrometry, 1H, 13C NMR, IR, and UV spectroscopy and mass-spectrometry. A study of the luminescent properties of the dye showed that it exhibits fluorescence in the near infrared region of the spectrum, which makes it a promising compound for use as an active emitting layer in NIR OLED as well as for other possible applications as an IR luminophore.

α-Cyanostilbene: A Multifunctional Spectral Engineering Motif

The remarkable photophysical phenomenon of aggregation-induced emission offers excellent strategies to obtain the molecular materials possessing unique spectral signatures such as high fluorescence intensity, excellent quantum yield, large Stokes shift...

Fluorescent Benzothiadiazole Derivatives as Fluorescence Imaging Dyes: A Decade of New Generation Probes

The current review describes advances in the use of fluorescent 2,1,3-benzothiadiazole (BTD) derivatives after nearly one decade since the first description of bioimaging experiments using this class of fluorogenic dyes. The review describes the use of BTD-containing fluorophores applied as, inter alia, bioprobes for imaging cell nuclei, mitochondria, lipid droplets, sensors, markers for proteins and related events, biological processes and activities, lysosomes, plasma membranes, multicellular models, and animals. A number of physicochemical and photophysical properties commonly observed for BTD fluorogenic structures are also described.

A Simple and Strong Electron-Deficient 5,6-Dicyano[2,1,3]benzothiadiazole-Cored Donor-Acceptor-Donor Compound for Efficient Near Infrared Thermally Activated Delayed Fluorescence

Despite the success of thermally activated delayed fluorescent (TADF) materials in steering the next generation of organic light-emitting diodes (OLEDs), effective near infrared (NIR) TADF emitters are still very rare. Here, we present a simple and extremely high electron-deficient compound, 5,6-dicyano[2,1,3]benzothiadiazole (CNBz), as a strong electron-accepting unit to develop a sufficiently strong donor-acceptor (D-A) interaction for NIR emission. End-capping with the electron-donating triphenylamine (TPA) unit created an effective D-A-D type system, giving rise to an efficient NIR TADF emissive molecule (λ_em =750 nm) with a very small ΔE_ST of 0.06 eV. The electroluminescent device using this NIR TADF emitter exhibited an excellent performance with a high maximum radiance of 10020 mW Sr^-1  m^-2 , a maximum EQE of 6.57% and a peak wavelength of 712 nm.

Design, Electron Transfer Process, and Opto-Electronic Property of Solar Cell Using Triphenylamine-Based D-π-A Architectures

A series of D-π-A type dyes were designed based on the experimentally synthesized A1 by introducing different functional groups on the donor and π-spacer, and the optical and electrical properties were calculated by using density functional theory (DFT) and time-dependent DFT (TD-DFT). P1⁻P6 present highest light harvesting efficiency (LHE), driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ) and e V O C . These critical parameters have a close relationship with the short-circuit current density ( J S C ) and open-circuit photovoltage ( V O C ), and lead to P1⁻P6 will exhibit higher efficiency. D4 also exhibit superior properties in the driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ), which will lead to a higher short-circuit current density ( J S C ). We hope that these results will be helpful for experiments to synthesize new and highly efficient dyes.

Energy level tuning of ‘Z’-shaped small molecular non-fullerene electron acceptors based on a dipyrrolo[2,3-b:2′,3′-e]pyrazine-2,6(1H,5H)-dione acceptor unit for organic photovoltaic applications: a joint experimental and DFT investigation on the effect of fluorination

Three dipyrrolo[2,3-b:2′,3′-e]pyrazine-2,6(1H,5H)-dione based small molecule non-fullerene acceptors with various end-capped fluorine units have been investigated.

A newly designed isoindigo/thiophene medium-sized molecule containing a π (D–A–D) bridge with unexpected organic photovoltaic performance

A novel medium-sized molecule BT(EDIDT3)2, has been synthesized using a Pd(AcO)₂ catalyzed direct C–H arylation method.

The impact of heteroatom substitution on cross-conjugation and its effect on the photovoltaic performance of DSSCs - a computational investigation of linear vs. cross-conjugated anchoring units

The unusual bonding pattern and proximal heteroatom substitution in π-cross conjugation produced distinct changes in the energy levels and photophysical behaviour of the dyes. To seek an understanding of the origin of these fluctuations, we have carried out a detailed computational investigation on a series of D-π1-π2 (A1)-A2 structured dyes comprised of common donor-spacer (auxiliary acceptor) units but varied the anchoring parts. In this study, we introduced a novel dimethylamino substituted fluorene-based triarylamine donor unit and evaluated its donating strength. Based on the comparison of DFT computed energy levels with experimental results, we have proposed an orbital splitting pattern to explain the energy level and photophysical properties of the linear vs. cross-conjugated dyes with respect to the linking position of the anchoring unit and benzo[1,2,5]thiadiazole (BTD) substitution. The smallest HOMO-LUMO gap of B3 mainly originated from the weak overlap of the directionality mismatch of the orbital interaction imposed by cross-conjugation. The inefficient overlap in B3 can possibly influence the energy levels but failed to enhance the charge transfer transitions upon photoexcitation. On the other hand, β-heteroatom substitution in bridged dyes partially enhanced π-delocalization over the cross conjugation and produced a significant ICT absorption with an optoelectronic response in the NIR region. BTD acceptor substitution increased the HOMO-LUMO gap of the bridged dyes. NBO analysis was performed to corroborate our predictions. DOS-PDOS analysis of the dyes@TiO2 was employed to investigate the electron injection rate of linear vs. bridged dyes. The anchoring pattern and large torsional deviation of the carboxylate anchoring group upon TiO2 adsorption drastically decreased the photovoltaic performance of the bridged dyes. The results obtained from this study provided a detailed understanding of how to surmount the cross-conjugation with the aid of β-heteroatom substitution. These design guidelines would be helpful in developing novel NIR dyes with better hole mobility for various optoelectronic applications. Furthermore, π-delocalization over the cross-conjugation concept opens a new pathway in the field of functional molecular devices to increase the charge conductance over several orders of magnitude with a significant reduction of destructive quantum interference at the molecular junction.

Direct observation of the rise of delayed fluorescence in dithienylbenzothiadiazole and its role in the excited state dynamics of a donor-acceptor-donor molecule

Dithienylbenzothiadiazole (DTBT) is used as a building block in several molecules having application in organic light emitting devices (OLED) and organic photovoltaic (OPV) devices. Delayed fluorescence (DF) is the preferred design principle employed currently in OLED research. DTBT has excellent delayed fluorescence properties which makes this moiety a potentially viable OLED material. Here, the dynamics of intersystem crossing (ISC) and reverse intersystem crossing (RISC) have been explored using fluorescence, phosphorescence, fluorescence lifetime and transient absorption measurements. Experimentally it is demonstrated that singlet and triplet states of DTBT are close lying or degenerate and after a certain time the molecules can stay in the singlet or the triplet state forming an equilibrium between the two states which hinders the identification of these two states that could be characterized by routine steady state fluorescence and phosphorescence studies. Similarly in OPV material research, DTBT is coupled with strong donors to form push-pull molecules to produce a prolonged charge separated state. In this study DTBT appended with carbazole at both ends (CDTBT) was used to study the dynamics of DTBT within a donor-acceptor-donor system. The study reveals similar kinds of ISC and RISC in CDTBT along with a competitive deactivation pathway of the singlet state and it was concluded to be through the formation of a charge separated species in CDTBT.

The role of π-linkers in tuning the optoelectronic properties of triphenylamine derivatives for solar cell applications - A DFT/TDDFT study

A recently reported triphenylamine (TPA) group in conjugation with a benzothiadiazole (BTD) moiety opens up the possibility for designing new organic sensitizers for solar cell applications that are amenable for structural tuning. Hence, seven new TPA molecules were designed from two experimentally reported molecules. The optoelectronic properties, including the absorption and emission spectra of the TPA derivatives, were studied via density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Different π-linkers were screened to understand the role of π-linkers in altering the optoelectronic properties of these molecules. Our results show that furan moieties bring planarity to the molecule and show reduced HOMO-LUMO gaps. All these molecules show excellent delocalization of π-electrons. TDDFT calculations show that furan-substituted TPA (TPA9) has the highest absorption maxima. Interestingly, the thiophene-substituted TPA (TPA7) was found to have a high emission maxima as it achieved planarity in the excited state. There is an excellent correlation observed between the computed optoelectronic properties and calculated HOMO-LUMO gaps. Overall, this study throws light on the role of π-linkers in the photophysical properties of TPA derivatives and provides useful clues in designing new molecules for optoelectronic applications.

Effects of the acceptor pattern and substitution position on the properties of N-phenyl-carbazolyl based donor–acceptor–donor molecules

Four D–A–D type molecules were designed and synthesized, and their specific properties including optical, redox and thermal stabilities were studied in detail. The influence of substitution and the heteroatom effects were also studied.

Rational design of cyclopenta[b]naphthalenes for better optoelectronic applications and their photophysical properties using DFT/TD-DFT methods

The optical properties of cyclopenta[b]naphthalenes (CPNs) can be fine-tuned by suitable substitutions and DFT calculations show that they can make efficient OLEDs.

Funnel shaped molecules containing benzo/pyrido[1,2,5]thiadiazole functionalities as peripheral acceptors for organic photovoltaic applications

Energy levels of a funnel shaped molecule was effected by varying donor and acceptor combinations and a power efficiency of 2.21% achieved for DCTP molecule.

A facile method to synthesize [A′(D′AD)2]-based push–pull small molecules for organic photovoltaics

Synthesis of promising new composition low band gap small molecules based on the push–pull (donor–acceptor) system, which displayed power conversion efficiency of up to 3.24%.