Organic Photovoltaic Applications Research Articles

Generation of Database of Polymer Acceptors and Machine Learning‐Assisted Screening of Efficient Candidates

ABSTRACTThis paper presents a comprehensive approach for designing polymer acceptors for organic photovoltaic applications through the generation of an extensive database and the application of machine learning (ML) techniques. Over 40 ML models are trained for the prediction of power conversion efficiency (PCE). Histgradient boosting regressor has appeared as best model. Almost 10 k polymers are generated and their PCE values are predicted. The chemical space of polymers has been visualized and analyzed. Cluster analysis revealed significant differences among the selected polymers. Additionally, an assessment of synthetic accessibility for these polymers indicated that the majority can be synthesized with relative ease.

Elucidating the Advancement in the Optoelectronics Characteristics of Benzoselenadiazole-Based A2-D-A1-D-A2-Type Nonfullerene Acceptors for Efficient Organic Solar Cells.

The potential applications of nonfullerene acceptors (NFAs) such as tunable band gaps, improved charge separation, wide-range absorption, enhanced power conversion efficiency, and operational stability make them highly favorable for organic photovoltaic applications. Herein, we designed eight novel structurally modified nonfused benzoselenadiazole (BSe)-based A2-D-A1-D-A2-type NFAs for efficient organic solar cells (OSCs). These newly modeled BSe-based NFA series contain BSe as the central core. We employed strong electron-withdrawing moieties at terminal acceptor A2 to further enhance the optical, optoelectronics, and photovoltaic characteristics of OSCs. These designed molecules (HNM1-HNM8) along with the synthetic reference molecule (HNM) were thoroughly characterized by using efficient and advanced quantum chemical simulation approaches. Thus, to ascertain the enhancement of both optical and photochemical response, a thorough density functional theory (DFT) study was carried out using the M062X level in association with the 6-31G(d,p) basis set. All of the investigated molecules (HNM1-HNM8) had their excited states calculated using the time-dependent density functional theory method. The newly designed molecules (HNM1-HNM8) presented narrower band gaps, improved absorption and optoelectronics properties, and reduced excitation and binding energies. The electrostatic potential, density of states, transition density matrix, ionization potential, and electron affinity analysis of this newly designed (HNM1-HNM8) series revealed a strong coherence with those of the reference HNM molecule. Electron density difference mapping allowed us to visualize the spatial movement of electrons between the donor and acceptor molecules during excitation. This insight helps us to understand the efficiency of charge separation and recombination processes that are critical for the performance of organic photovoltaics. The reorganization energy and charge transfer analysis suggests that HNM1-HNM8 molecules could act as NFAs for organic photovoltaic applications to enhance their efficiency further. The donor: acceptor charge transfer analysis was also carried out, which revealed that the PTB7-Th:HNM2 donor:acceptor complex shows a great charge transportation process at the donor-acceptor interface. Moreover, the photovoltaic analysis shows that the designed (HNM1-HNM8) NFA series has a great potential to produce improved open-circuit voltage and fill factor values, which may be helpful in enhancing the overall PCEs of the OSCs.

Design and fabrication of high-performance poly (p-phenylene azomethine) films for advanced organic photovoltaic applications

Design and fabrication of high-performance poly (p-phenylene azomethine) films for advanced organic photovoltaic applications

Novel low‐band gap non‐fullerene acceptors based on IDIC core as potential photovoltaic materials

AbstractThree novel non‐fullerene acceptors (NFAs) (PhBu‐IDT‐BT‐IC, PhBu‐IDT‐BT‐IC4F and PhBu‐IDT‐BT‐IC4Cl) based on 3,8‐dioctyl‐indaceno[1,2‐b:5,6‐b’]dithiophene (IDT) core have been designed and synthesized with and without halogen (F and Cl) substitution. The NFAs showed high thermal stability. The ultraviolet–visible absorption studies in solution and thin film for the three acceptors revealed maximum absorption from 687 to 732 nm and 731 to 847 nm, respectively. The onset of absorption in the thin film was found to be extending up to around 960 nm for PhBu‐IDT‐BT‐IC4Cl. The optical band gap ranged from 1.30 to 1.41 eV, which are very low and useful for photovoltaic application. The introduction of halogen appreciably altered the LUMO energy levels, whereas the HOMO energy levels were nearly intact. These small molecule non‐fullerene acceptors could be used as potential acceptors in bulk heterojunction organic photovoltaic (BHJ‐OPV) applications.

Tuning of Optoelectronic Characteristics of Quinoxalineimide-based Novel Non-Fullerene Acceptors for Organic Photovoltaic Applications

Organic solar cells (OSCs) have made remarkable progress due to developing novel materials and device architectures. Herein, we designed six new non-fullerene acceptors (QM1–QM6) having a quinoxalineimide (QI) as the central-building-block. We aimed to explore the potential of QI-containing structures for developing high-performance acceptors for OSCs. These designed molecules possess a fusion of the QI unit with a thienylthiophene backbone and are equipped with various efficient end-capping groups. Extensive theoretical calculations were carried out to evaluate the structural and charge distribution characteristics, including the optical, optoelectronics, density of states, transition density matrix, molecular electrostatic potential (ESP), reorganization energies, and photovoltaic properties. The results revealed that the designed series exhibited improved electron–hole pair coherences, efficient charge transportation, and favorable ESP patterns, suggesting their suitability for enhanced optical and electronic characteristics. Furthermore, the hole and electron overlap analyses demonstrated significant overlap in QM1–QM6, indicating efficient charge transfer and higher charge mobilities. Additionally, the analysis of reorganization energies showed low reorganization energy values, indicating favorable charge mobility rates and potential for high-efficiency solar cell devices. This research establishes a strong foundation for utilizing QI-containing fused units as central building blocks for designing high-performance acceptors, opening up new avenues for advancements in OSCs technology.

Elucidating the potential of nitrogen-containing heterocyclic core-based non-fullerene acceptors for organic photovoltaic applications

Intramolecular noncovalent interactions are recognized as an efficient route to construct non-fused-core-based non-fullerene acceptors (NFAs) for efficient and cost-effective organic solar cells (OSCs). Herein, we engineered ten distinct structured NFAs molecules based on nitrogen-containing six-membered heterocycle cores. We incorporated various efficient functional groups into the synthetic reference molecule (RM) to design a new efficient series of NFAs (RM1-RM10). These materials are intensively investigated by performing advanced quantum chemical simulations, and the results are compared with those of synthetic RM molecules. We revealed the potential of these materials by investigating their optical, electronic, optoelectronic, and photovoltaic characteristics. By implementing various theoretical models, we explore the inner hidden potential of this designed series (RM1-RM10), such as density of state, transition density matrix, and electrostatic potential studies have been performed. Our applied theoretical modeling approach enables these photovoltaic materials (RM1-RM10) to have customized attributes by tuning their energy levels, binding energy, optical features, and also the photovoltaic characteristics of these materials. Newly developed molecules (RM1-RM10) show promising optoelectronic properties, including a lower energy gap (ranging from 1.81 eV to 1.63 eV) and an absorbed maximum absorption wavelength (760.36 nm), compared to the reference values, which have an energy gap of 1.81 eV and a wavelength of 684.16 nm. Moreover, to demonstrate the charge transfer behavior of these materials, a donor: acceptor (PTB7-Th:RM9) complex study is also performed to reveal the charge transfer phenomenon at the donor: acceptor interface. Therefore, our presented molecular modeling strategy holds significant potential for manufacturing materials with tailored qualities, which is crucial in advancing the organic photovoltaics field.

Molecular Design and Organic Photovoltaic Applications of Carboxylate‐Functionalized P‐type Polymers

AbstractThe significant progress of p‐type and n‐type active layer materials in the past several years has pushed the power conversion efficiency (PCE) of organic solar cells (OSCs) toward 19%. Due to the relatively low synthesis cost and simple synthesis method of carboxylate‐containing building blocks, including thiophene, thieno[3,2‐b]thiophene, thieno[3,4‐b]thiophene, furan, pyrazine, benzodithiophene, benzothiazole, quinoxaline, etc., are widely used to construct p‐type photovoltaic polymers. These resulting carboxylate‐bearing polymers present downward energy levels, high absorption coefficient, narrow bandgap, high hole mobility, and strong aggregation behavior, which have dabbled in the fabrication of mechanically stretchable, semitransparent, indoor, and tandem OSCs, etc., and produce excellent photovoltaic performance. The low‐cost carboxylate‐containing copolymers exhibit a satisfying PCE approaching 17%, and the random terpolymer systems achieve a high PCE over 19%. This review focuses on the progress of carboxylate‐containing photovoltaic polymers, summarizes the molecular characteristics, discusses their structure‐performance relationship, and offers a summary and outlook on the challenges for future molecular development.

Advancements in conjugated polymer research: applications in organic photovoltaics and field effect transistors

This review provides a comprehensive overview of the development and applications of conjugated polymer semiconductors. The review summarizes the current state of research in this field, including the synthesis and characterization of these materials, their properties, and potential applications. The scope covers a wide range of topics, including organic photovoltaics, organic field-effect transistors, and conjugated polymer nanoparticles. The main findings highlight the significant progress that has been made in this field, with conjugated polymers exhibiting favorable electronic and optical properties, as well as high charge mobility. These materials have shown great potential for use in various applications, including solar cells, light-emitting diodes, and field-effect transistors. The applications are far-reaching, with the potential to revolutionize the electronics industry by providing low-cost, flexible, and environmentally friendly alternatives to traditional inorganic materials. One of the key challenges facing this field is the need to improve the efficiency and stability of conjugated polymer-based devices. While significant progress has been made in this area, there is still much work to be done to develop materials and device architectures that can achieve high performance over extended periods of time. Another challenge is the need to develop scalable manufacturing processes that can produce large quantities of high-quality conjugated polymers at a reasonable cost. The continued advancement of this field holds great promise for the development of new technologies that can improve our lives and help to address some of the world’s most pressing challenges.

Introducing the new concept of a chiral-polaron giant-IRAV signature, optical-active giant-response in vibrational circular dichroism.

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds of primary importance in the field of organic semiconductors, with applications in both organic electronics and photovoltaics. This paper delves into two strictly related topics. First, the theoretical rationalization of the physical factors underlying the emergence of the polaron "giant-response infrared active vibrations (IRAVs)" signature in positively charged PAHs. Results are presented concerning the tight comparison between the experimental results and theoretical results obtained within different DFT paradigms (BLYP, B3LYP, CAM-B3LYP and LC-BLYP) and the pure Hartree-Fock Hamiltonian. This allowed the rationalization of the emergence of the giant IRAV response as essentially propelled by long-range electronic interactions. Moreover, the role of vibrational modes and molecular dimensions (topology) is addressed. Second, the analysis is extended to chiral [4]helicene. This allows the introduction of a new concept yet to be explored experimentally: the chiral-polaron giant-IRAV signature in vibrational circular dichroism (VCD) spectra.

Pyrazino[2,3-g]quinoxaline core-based organic liquid crystalline semiconductor: Proficient hole transporting material for optoelectronic devices

Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.

Performance optimization of active layer doped P3HT:PCBM nanoparticles for organic photovoltaic cell applications

Performance optimization of active layer doped P3HT:PCBM nanoparticles for organic photovoltaic cell applications

Non-fused nonfullerene acceptors based on thieno[2',3':4,5]thieno[3,2-b]indole for efficient organic solar cells

Thieno[3,2-b]indole (TI) has attracted more and more attention in organic electronics. Herein, thieno[2',3':4,5]thieno[3,2-b]indole (TTI), as a tetracyclic derivative of TI, was been developed by fused another thiophene unit. Furtherly, two non-fused NFAs TTI-2F and TTI-2Cl based on TTI have been synthesized via simple and easy synthetic routes. TTI-2F and TTI-2Cl both exhibited excellent thermal stability, low optical bandgaps of ∼1.5 eV, nearly planar molecular geometries, and suitable energy levels. As a result, PM6:TTI-2F solar cells afforded a decent PCE of 10.67 %, with an VOC of 0.935 V, a JSC of 19.21 mA/cm2 and a FF of 59.40 %, which was due to the suitable intermolecular interactions, higher HOMO energy level, better exciton dissociation, suppressed trap-assisted recombination, and balanced charge carrier mobilities. As comparison, PM6:TTI-2Cl cell exhibited much lower PCE of 8.34 %. These results demonstrated that NFAs based on TTI are promising for industrialized organic photovoltaic applications due to the simple synthesis and decent photovoltaic performance.

Modeling of Conjugated Core-Based Non-Fullerene Acceptor Materials for Organic Photovoltaic Applications

Non-Fullerene acceptors (NFAs) are attracting much attention from scientists worldwide for their potential use in organic solar cells (OSC). Herein, we developed C-shaped NFAs acceptors (FA1–FA10) by performing end-capped alteration on GL1. The structural-property relation and optoelectronic characteristics were examined theoretically. Furthermore, the impact of structural changes on the optoelectronic characteristics of FA1–FA10 molecules was investigated by using density functional theory (DFT), and time-dependent DFT. The photo-physical and optoelectronic features such as frontier molecular orbitals, electron–hole overlapping, excitation and binding energy, molecular electrostatic potential, the density of states, transition density matrix, open circuit voltage, and reorganization energies of hole and electron, of the designed materials have been simulated. Compared to GL1 (R), the developed materials displayed a red-shifted absorption (ranges 769.84–856.36[Formula: see text]nm), better electric-charge movement, lower binding (0.30[Formula: see text]eV), and excitation energies (1.28[Formula: see text]eV), and narrower bandgaps (ranges 1.59–1.79[Formula: see text]eV), respectively. Therefore, we suggest these to synthetic researchers for the future development of efficient OSCs.

Eco-Friendly Solvent-Processed Dithienosilicon-Bridged Carbazole-Based Small-Molecule Acceptors Achieved over 25.7% PCE in Ternary Devices under Indoor Conditions.

Terminal acceptor atoms and side-chain functionalization play a vital role in the construction of efficient nonfullerene small-molecule acceptors (NF-SMAs) for AM1.5G/indoor organic photovoltaic (OPV) applications. In this work, we report three dithienosilicon-bridged carbazole-based (DTSiC) ladder-type (A-DD'D-A) NF-SMAs for AM1.5G/indoor OPVs. First, we synthesize DTSiC-4F and DTSiC-2M, which are composed of a fused DTSiC-based central core with difluorinated 1,1-dicyanomethylene-3-indanone (2F-IC) and methylated IC (M-IC) end groups, respectively. Then, alkoxy chains are introduced in the fused carbazole backbone of DTSiC-4F to form DTSiCODe-4F. From solution to film absorption, DTSiC-4F exhibits a bathochromic shift with strong π-π interactions, which improves the short-circuit current density (Jsc) and the fill factor (FF). On the other hand, DTSiC-2M and DTSiCODe-4F display up-shifting lowest unoccupied molecular orbital (LUMO) energy levels, which enhances the open-circuit voltage (Voc). As a result, under both AM1.5G/indoor conditions, the devices based on PM7:DTSiC-4F, PM7:DTSiC-2M, and PM7:DTSiCOCe-4F show power conversion efficiencies (PCEs) of 13.13/21.80%, 8.62/20.02, and 9.41/20.56%, respectively. Furthermore, the addition of a third component to the active layer of binary devices is also a simple and efficient strategy to achieve higher photovoltaic efficiencies. Therefore, the conjugated polymer donor PTO2 is introduced into the PM7:DTSiC-4F active layer because of the hypsochromically shifted complementary absorption, deep highest occupied molecular orbital (HOMO) energy level, good miscibility with PM7 and DTSiC-4F, and optimal film morphology. The resulting ternary OSC device based on PTO2:PM7:DTSiC-4F can improve exciton generation, phase separation, charge transport, and charge extraction. As a consequence, the PTO2:PM7:DTSiC-4F-based ternary device achieves an outstanding PCE of 13.33/25.70% under AM1.5G/indoor conditions. As far as we know, the obtained PCE results under indoor conditions are one of the best binary/ternary-based systems processed from eco-friendly solvents.

First theoretical engineering of robust C-C single bond-based acceptor materials for efficient organic photovoltaics

Organic photovoltaics with prolonged photo stability need further attention from researchers around the world. In this report, a new series of photostable acceptor molecules for possible applications in organic photovoltaics have been presented. In these molecules, a robust carbon–carbon single bond initiates a unique N---S covalent interaction that enhances the photo and thermal stability of the studied designed systems. In this regard, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been employed at different appropriate levels. The position of frontier molecular orbitals (FMOs) reduces the band gap with maximum charge transportation. Further, the modeled systems have also shown light absorption in the near infra-red (IR) region with easy excitation of the exciton. High electron and hole mobilities towards the respective electrodes are also noted for the studied systems (SSFL-1 to SSFL-4). Finally, enhanced fill factor (FF%) along with high power conversion efficiency (PCE) of 21.36 % is noted in the designed systems.

Designing and theoretical study of benzocarbazole-based D-π-D type small molecules donor for organic solar cells

Seven new molecules (S1–S7) of D-π-D type have been designed for organic photovoltaic applications. The DFT and TD-DFT methods were used to investigate the effect of different central bridge groups on the geometric, optoelectronic, and charge transport properties of the constructed molecules. Among them, S4 and S6 have the lowest energy band gap and a red shift in the absorption spectra, revealing the perfect relationship between the central bridge and the strong electron withdrawal character through extended conjugation. Similarly, S6 explored the lowest reorganization energy (RE) value for electron and hole revealing its enhanced charge transition, also shows better ICT characteristics with its highest NLO properties. Compound S4 showed the smallest value of ΔEL−L and Eb, and the highest Voc due to its low HOMO, which improves the photocurrent density of the devices. Thus, the results suggest that bridge modification is a practical strategy to improve the efficiency of OSCs.

Thermally activated motion of cold excitons in conjugated polymers

AbstractThermally activated migration of localized cold excitons were investigated in archetypal conjugated polymers; trans‐polyacetylene, polythiophene, and poly(p‐phenylene vinylene). Room temperature thermal energy has been found to provide sufficient energy to avail substantial mobility for excitons. A simple undistorted but displaced harmonic oscillator model has been assumed to predict the activation energy for exciton hopping between identical sites in perfectly planar conjugated chains, promoted by vibrational modes with Bu symmetry. The activation energies of exciton hopping has been found to increase in the order of trans‐polyacetylene (6.4 meV), polythiophene (29.5 meV), and poly(p‐phenylene vinylene) (147.4 meV). A rough Monte‐Carlo simulation based on incoherent hopping mechanism reveals excitons can displace in an average of 2.17 nm in polythiophene whereas those distances are much smaller in poly(p‐phenylene vinylene) (0.24 nm) and trans‐polyacetylene (0.37 nm). The simulation results partially explain why polythiophene based polymers are better suited for organic photovoltaic applications whereas poly(p‐phenylene vinylene) are more appropriate for organic light emitting diode applications.

Photovoltaic Properties of π-Conjugated Polymers Based on Fused Cyclic Imide and Amide Skeletons

Abstract π-Conjugated polymers P(BDT-BTI) and P(BDT-BTA) bearing cyclic imide and amide (lactam) moieties, respectively, were designed and synthesized for application in organic photovoltaics (OPVs). Introducing electron-withdrawing imide and amide moieties lowers the HOMO energy levels of the polymers, resulting in an increase in the open-circuit voltages of OPVs. Complementary photoabsorption over the entire visible range was achieved by combining P(BDT-BTI) and P(BDT-BTA) with a typical non-fullerene acceptor, IT-4F. Unlike P(BDT-BTI), P(BDT-BTA) tends to maintain high crystallinity and retains π–π stacking interactions and face-on orientation in the blend films with IT-4F. Consequently, OPVs based on P(BDT-BTA):IT-4F blends achieved power conversion efficiencies as high as 9.6% without any processing additives or post-treatments.

Theoretical framework for achieving high V oc in non-fused non-fullerene terthiophene-based end-capped modified derivatives for potential applications in organic photovoltaics.

Non-fused ring-based OSCs are an excellent choice, which is attributed to their low cost and flexibility in applications. However, developing efficient and stable non-fused ring-based OSCs is still a big challenge. In this work, with the intent to increase V oc for enhanced performance, seven new molecules derived from a pre-existing A-D-A type A3T-5 molecule are proposed. Different important optical, electronic and efficiency-related attributes of molecules are studied using the DFT approach. It is discovered that newly devised molecules possess the optimum features required to construct proficient OSCs. They possess a small band gap ranging from 2.22-2.29 eV and planar geometries. Six of seven newly proposed molecules have less excitation energy, a higher absorption coefficient and higher dipole moment than A3T-5 in both gaseous and solvent phases. The A3T-7 molecule exhibited the maximum improvement in optoelectronic properties showing the highest λ max at 697 nm and the lowest E x of 1.77 eV. The proposed molecules have lower ionization potential values, reorganization energies of electrons and interaction coefficients than the A3T-5 molecule. The V oc of six newly developed molecules is higher (V oc ranging from 1.46-1.72 eV) than that of A3T-5 (V oc = 1.55 eV). Similarly, almost all the proposed molecules except W6 exhibited improvement in fill factor compared to the A3T-5 reference. This remarkable improvement in efficiency-associated parameters (V oc and FF) proves that these molecules can be successfully used as an advanced version of terthiophene-based OSCs in the future.

A paradigm study of polymer donor diluted bulk heterojunction films for application in semitransparent organic photovoltaics

More J-type polymer aggregations and the prioritized polymer reduction from its pure domain help to achieve high LUE in ST-OSCs during the polymer donor diluting process.