Thiophene Units Research Articles

Mono-/Bimetallic Neutral Iridium(III) Complexes Bearing Diketopyrrolopyrrole-Substituted N-Heterocyclic Carbene Ligands: Synthesis and Photophysics.

The synthesis and photophysics (UV-vis absorption, emission, and transient absorption) of four neutral heteroleptic cyclometalated iridium(III) complexes (Ir-1-Ir-4) incorporating thiophene/selenophene-diketopyrrolopyrrole (DPP)-substituted N-heterocyclic carbene (NHC) ancillary ligands are reported. The effects of thiophene versus selenophene substitution on DPP and bis- versus monoiridium(III) complexation on the photophysics of these complexes were systematically investigated via spectroscopic techniques and density functional theory calculations. All complexes exhibited strong vibronically resolved absorption in the regions of 500-700 nm and fluorescence at 600-770 nm, and both are predominantly originated from the DPP-NHC ligand. Complexation induced a pronounced red shift of this low-energy absorption band and the fluorescence band with respect to their corresponding ligands due to the improved planarity and extended π-conjugation in the DPP-NHC ligand. Replacing the thiophene units by selenophenes and/or biscomplexation led to the red-shifted absorption and fluorescence spectra, accompanied by the reduced fluorescence lifetime and quantum yield and enhanced population of the triplet excited states, as reflected by the stronger triplet excited-state absorption and singlet oxygen generation.

Effect of oligothiophene π-bridge length in D-π-A star-shaped small molecules on properties and photovoltaic performance in single-component and bulk heterojunction organic solar cells and photodetectors

Donor-acceptor molecules with thiophene fragments as the π-bridge represent a promising class of materials for organic photovoltaics especially in single-component (SC) organic solar cells (OSCs) and other related applications. However, the effect of the oligothiophene π-bridge length on physicochemical properties, photophysics, charge transport, and photovoltaic performance of these materials has not been thoroughly addressed. Here, we report on the synthesis and comprehensive investigation of the series of star-shaped donor-acceptor molecules (0T–4T) with triphenylamine as a donor core linked through an oligothiophene π-bridge of variable length to the terminal hexyl-dicyanovinyl electron-withdrawing groups. We found that variation of the π-bridge length from 0 to 4 thiophene units strongly impacts their properties such as the solubility, highest occupied molecular orbital energy, optical absorption and photophysics, film morphology, phase behavior, and molecular packing as well as the charge carrier mobility. The performance of the SC and bulk heterojunction OSCs and photodetectors is comprehensively studied and compared. The results obtained provide insight into how to fine-tune and predict properties and photovoltaic performance of small molecules for organic solar cells and photodetectors.

Syntheses of thiophene appended N-confused phlorin isomers

A doubly confused thiapentapyrrane NSP-5 was synthesized by acid-catalysed condensation. Subsequent oxidation with DDQ did not afford the expected thiasapphyrin-like product. Instead, two tetrapyrrolic macrocycles, i.e. neo-N-confused phlorin (1) and N-confused phlorin-II (2) were obtained in the yields of 14% and 18%, respectively. The compounds were characterized by NMR, HRMS, and X-ray diffraction analyses. Single crystal structures clearly reveal that the thienyl units are not embedded into the macrocycles, but appended as meso-substituents, and the C[Formula: see text]-N and C[Formula: see text]-C[Formula: see text] cyclization modes can be clearly revealed by the crystal structures of 1 and 2, respectively. The observation that the thienyl unit is not involved in oxidative cyclization may be related to the relatively low reactivity of the thiophene moiety compared with the more electron-rich pyrrole unit. These results indicate that oxidative cyclization of linear thiaoligopyrranes containing terminal thiophene units may be developed as an effective approach for synthesizing nonconjugated macrocycles like phlorin analogues.

Regio-regular poly(thienylene vinylene)s (rr-PTVs) through acyclic diene metathesis (ADMET) polymerization and the impact of alkyl side-chains on polymer molecular weight and solubility

Poly(thienylene vinylene) (PTV) is one of the prototypical conjugated polymers (CPs) that has received relatively little attention. The insertion of one small double bond between every pair of adjacent thiophene units in PTV structures potentially allow direct functionalization of the thienyl rings, which can fine-tune polymer electronic properties without significantly impact main-chain planarity. However, synthetic methods leading to such tailor-designed PTVs are scarce. In this paper, we report a new synthetic strategy that produces a series of regio-regular (rr) PTVs bearing bromine atoms and different alkyl side-chains on every thiophene unit. The methodology starts with synthesis of well-defined dimeric monomers that lead to rr-PTVs upon ADMET polymerization. The monomers and polymers are fully characterized by NMR and absorption spectroscopy. We found that linear and slightly branched alkyl chains led to precipitation during the polymerization process and thus low apparent molecular weight due to limited polymer solubility, while long-branched and bulky silyl-alkyl ether chains led to PTVs with greater solubility and higher molecular weights.

Benzodithiophene-Fused Cyclopentannulated Aromatics via a Palladium-Catalyzed Cyclopentannulation and Scholl Cyclodehydrogenation Strategy.

We report the synthesis of a new class of cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) incorporating fused benzodithiophene subunits. These CP-PAHs were prepared utilizing a two-step process involving a palladium catalyzed cyclopentannulation followed by a Scholl cyclodehydrogenation. This work broadens the scope of annulation chemistry by employing 1,2-bis(5-hexylthiophen-3-yl)ethyne and dibromoaryl derivatives based on anthracene, pyrene, and perylene to give 4,4',4'',4'''-(cyclopenta[hi]aceanthrylene-1,2,6,7-tetrayl)tetrakis(2-hexylthiophene), 4,4',4'',4'''-(dicyclopenta[cd,jk]pyrene-1,2,6,7-tetrayl)tetrakis(2-hexylthiophene), and 1,2,7,8-tetrakis(5-hexylthiophen-3-yl)-1,2,7,8-tetrahydrodicyclopenta[cd,lm]perylene. Scholl cyclodehydrogenation of the pendant thiophene units provided access to the π-extended polyaromatic systems 2,5,11,14-tetrahexylrubiceno[5,4-b:6,7-b':12,11-b'':13,14-b''']tetrathiophene, 2,5,11,14-tetrahexyldithieno-[4,5:6,7]indeno[1,2,3-cd]dithieno[4,5:6,7]indeno-[1,2,3-jk]pyrenes, and 2,9,12,19-tetrahexyldithieno[4,5:6,7]indaceno[1,2,3-cd]dithieno[4,5:6,7]indaceno[1,2,3-lm]perylene that possess helicene-like fragments. The anthracene-based CP-PAH was contorted owing to [5]helicene-like arrangements, while the pyrene- and perylene-based systems were essentially planar. The fully conjugated small molecules give low optical gaps (1.7-2.1 eV) with broad light absorption. The HOMO and LUMO energies of the CP-PAHs were found to be in the range of -5.48 to -5.05 eV and -3.48 to -3.14 eV, respectively. Finally, the anthracene-based CP-PAH was found to be a p-type semiconductor when tested in an organic field effect transistor.

Dopant‐Free Ternary Conjugated Polymeric Hole‐Transporting Materials for Efficient Inverted Planar Perovskite Solar Cells

In inverted perovskite solar cells (PSCs), hole transport materials (HTMs) can efficiently improve hole extraction and transfer as well as the crystallization of perovskite films and thus enhance the photovoltaic performance. Herein, two dopant‐free, regular A1–D–A2–D‐type (D: electron donor; A: electron acceptor) polymeric HTMs, PTPDTBT and PDPPTBT, are developed by integrating the benzothiadiazole unit (A1) with the electron‐accepting species of either a thieno[3,4‐c]pyrrole‐4,6‐dione or a pyrrolo[3,4‐c]pyrrole‐1,4‐dione segment (A2), respectively, where the thiophene unit (D) results in a kinked molecular geometry. These A1–D–A2–D‐type terpolymers exhibit comparable nonpolar properties but distinct film‐quality morphology and charge transport characteristics. PDPPTBT with the more insulating side‐chain groups is found to improve the quality of perovskite films cast on top with larger grain sizes and more homogeneous crystallization. As a consequence, the PDPPTBT‐based PSCs without any dopants and additional interlayers display a champion power conversion efficiency of 18.17%, one of the highest values of MAPbI3‐based inverted PSCs using dopant‐free D‐A‐type polymeric HTMs. Furthermore, the PDPPTBT‐based device exhibits negligible hysteresis and high long‐term stability. This work provides a potential strategy to design dopant‐free A1–D–A2–D‐type polymeric HTMs for efficient and stable PSCs.

Infrared Spectral Analysis of Plasmonic Polarons in Doped P3HT Films

The strong midinfrared polaronic signal in p‐doped polymers such as P3HT is analyzed in terms of a plasmonic absorption cross section. Quantitative conclusion on the hole mobility along chains of coherently connected thiophene units is derived in that way. This intrachain mobility is more than two orders of magnitude higher than average mobilities of doped polymers which is limited by the much less efficient interchain transport processes.

Oligothiophene Phosphonic Acids for Self-Assembled Monolayer Field-Effect Transistors.

Semiconducting self-assembled monolayers (SAMs) represent highly relevant components for the fabrication of organic thin-film electronics because they enable the precise formation of active π-conjugates in terms of orientation and layer thickness. In this work, we demonstrate self-assembled monolayer field-effect transistors (SAMFETs) composed of phosphonic acid oligomers of 3-hexylthiophene (oligothiophenes-OT) with systematic variations of thiophene repeating units (5, 10, and 20). The devices exhibit stable lateral charge transport with increased mobility as a function of thiophene unit counts. Importantly, our work reveals the packing and intermolecular order of varied-chain-length SAMs at the molecular scale via X-ray reflectivity (XRR) and quantitative X-ray photoelectron spectroscopy (XPS). Short oligomers (OT5-PA and OT10-PA) arrange almost perpendicular to the substrate, forming highly ordered SAMs, whereas the long-chain OT20-PA exhibits a folded structure. By tuning the molecular order in the monolayers via the SAM substitution reaction, the OT20-PA devices show a tripling in mobility.

Neutral Black Color Showing Electrochromic Copolymer based on Dithienopyrroles and Benzothiadiazole Derivatives

A novel monomer of 4-(4H-dithieno[3,2-b:2′,3′-d]pyrrol-4-yl)-N,N-dimethylaniline (TPDA) based on pyrrole and thiophene units was designed and synthesized, with the homopolymer and copolymer with 4,7-di(2,3-dihydro-thieno[3,4-b][1,4]dioxin-5-yl)benzo[1,2,5]thiadiazole (BDT) prepared by an electrochemical method. Both polymers exhibited good electrochemical properties. Spectroelectrochemical features were investigated using an electrochemical station and UV–vis spectrophotometer. PTPDA film showed orange color in the neutral state and blue color for the oxidation state while PBDT film exhibits a neutral green color and light blue for the oxidation state. The copolymer film can cover the entire visible region due to its possessing the absorption features of both PTPDA and PBDT films, which exhibits black color in the neutral state (0 V) and blue color in the oxidation state (1.0 V). In addition, both the homopolymer and copolymer exhibit good electrochemical stability and coloration efficiency. These electrochromic properties make them as potential candidates for applications.

Effects of electron-withdrawing group and π-conjugation length in donor-acceptor oligothiophenes on their properties and performance in non-fullerene organic solar cells

The development of small-molecule donor materials for highly efficient non-fullerene (NF) organic solar cells (OSC) remains an urgent research task. In this work, the synthesis of donor-acceptor molecules containing either five (5T) or seven (7T) thiophene units end-capped with methyl dicyanovinyl (DCV) or ethyl cyanoacetate (CNA) electron-withdrawing groups was reported. Their thermal stability, phase behaviour, optical and electrochemical properties as well as photovoltaic performance in blends with IDIC or Y6 as acceptor materials were comprehensively investigated and compared. All of the obtained donor molecules are characterized by high thermal stability, efficient sunlight absorption and excellent solubility in combination with a good crystallinity. The results obtained allowed us to reveal the impact of the oligothiophene conjugation length and type of electron-withdrawing group on the properties and performance of the D-A oligothiophenes in NF OSC. The results clearly demonstrate that the devices based on donor molecules with 7T or CNA fragments significantly outperform those based on 5T or DCV groups.

Electrochromic polymers based on 2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene and thiophene derivatives as potential anodic layers for high performance electrochromic devices

A 2,5-di(2-thienyl)thieno[3,2-b]thiophene (dTT)-containing homopolymer (PdTT) and four dTT-containing copolymers (P(dTT-co-bTp (2,2′-bithiophene)), P(dTT-co-TF), P(dTT-co-CPdT) and P(dTT-co-CPdTK)) were polymerized using electrochemical method and their electrochromic switching properties were explored. dTT shows lower onset oxidized potential (Eonset) than that of bTp, conjecturing that dTT displays more extended conjugated degree than that of bTp ring. PdTT film presents camel, olive green, and dark blue at 0.0, 0.8 and 1.0 V, respectively. Colorful-to-colorless switching investigations of polymeric films display that P(dTT-co-bTp) has high △T (41.3% at 1070 nm) and η (149.4 cm2/C at 1070 nm) in 0.2 M LiClO4/ACN/DCM solution. Five dual-layer complementary electrochromic devices based on PdTT, P(dTT-co-bTp), P(dTT-co-TF), P(dTT-co-CPdT) or P(dTT-co-CPdTK) as the anodic layer and PEDOT-PSS as the cathodic layer are assembled. P(dTT-co-TF)/PEDOT-PSS ECD exhibits high △T (44.7% at 680 nm) and satisfactory electrochemical redox stability, while P(dTT-co-CPdT)/PEDOT-PSS ECD displays high η (656.5 cm2/C at 686 nm) and rapid switching time (≤ 0.9 s). On the basis of these findings, the present work offers new structural insights for significant design of large contrast and multicolored electrochromic electrodes.Background: The thieno[3,2-b]thiophene (TT) unit is a fused heterocyclic ring, its coplanar structure and electron-donating ability can enhance carrier transporting properties of polymer chain. A 2,5-di(2-thienyl)thieno[3,2-b]thiophene (dTT) unit displays more extended conjugated degree than that of bTp, it is interesting to explore the multichromic behaviors of five dTT-based polymers and their corresponding ECDs upon applying various potentials.Methods: A dTT-containing homopolymer (PdTT) and four dTT-containing copolymers (P(dTT-co-bTp), P(dTT-co-TF), P(dTT-co-CPdT) and P(dTT-co-CPdTK)) are polymerized using electrochemical method. The spectral properties, kinetic characterizations, open-circuit memory, and electrochemical redox stability of PdTT/PEDOT-PSS, P(dTT-co-bTp)/PEDOT-PSS, P(dTT-co-TF)/PEDOT-PSS, P(dTT-co-CPdT)/PEDOT-PSS and P(dTT-co-CPdTK)/PEDOT-PSS ECDs are systematically studied.Significant Findings: The present work offers new structural insights for significant design of large contrast and multicolored electrochromic electrodes.

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

Azatriphenylene-based D-A-D-typed hole-transporting materials for perovskite solar cells with tunable energy levels and high mobility

Computational study on relationship between molecular structure and property of small molecule hole-transporting materials (HTMs) is an efficient pathway to acquire potential HTMs for perovskite solar cells (PSCs). Herein, by conjugating the acceptor groups of electron-deficient diazatriphenylene (DAT), tetraazatriphenylene (TAT) and hexaazatriphenylene (HAT), and p-methoxy-substituted triphenylamine (MeOTPA) electron-donors, six novel donor–acceptor-donor (D-A-D) typed HTMs (SM11 ~ SM16) are designed. Furthermore, three thiophene-substituted acceptors (SM17 ~ SM19) are also investigated. The influences of acceptor moiety on the performance of HTMs are studied by carrying out theoretical chemical calculations. Compared with the reported HTM with triphenylene unit (TPH-T), the new tailored HTMs (SM11 ~ SM19) exhibit more negative highest occupied molecular orbital (HOMO) energy levels and slightly red-shifted light absorption due to the increased electron-deficient property of acceptor group and linked positions with the MeOTPA-donor. Meanwhile, our results show that the small torsion angle between the acceptor and the donor is beneficial to promote the hole transport in HTMs, and the thiophene units on acceptor may also be helpful to enhance the charge mobility of HTMs. In addition, the large charge transfer amounts and small exciton binding energies are found for designed HTMs, which will be favorable to facilitate the electron-hole separation in HTMs. The stability of HTMs may be decreased based on the calculated results of electrostatic surface potential and absolute hardness. We hope this work could highlight the potential of azatriphenylene acceptor-based D-A-D typed HTMs for efficient PSCs.

Recent progress in small‐molecule donors for non‐fullerene all‐small‐molecule organic solar cells

AbstractAll‐small‐molecule organic solar cells (all‐SM OSCs), with p‐type small molecule (p‐SM) as donor and n‐type small molecule (n‐SM) as acceptor, have drawn intensive research interests in recent years. All‐SM OSCs show advantages to their polymer counterparts, including well‐defined chemical structure, easy purification, and better repeatability in devices. The highest power conversion efficiency (PCE) of all‐SM OSCs has increased quickly to over 15% nowadays. In this review, we just summarize the progress of non‐fullerene all‐SM OSCs (NF all‐SM OSCs) in recent five years, by dividing small‐molecule donors into four categories based on the molecular segments of oligothiophene, benzo[1,2‐b:4,5‐b’]dithiophene (BDT) trimer, typical BDT‐central unit connected with π‐bridges of thiophene or electron deficient acceptor units. We aim to illustrate the relationship of molecular structures, properties, and device performance of small‐molecule donors with those different molecular segments. Furthermore, the tendency of molecular design for photo‐active materials are also depicted and summarized. Finally, we give our views on the future prospects of NF all‐SM OSCs to design the next‐generation OSCs.

Tris(pentafluorophenyl)borane‐Modified P3CT‐K as an Efficient Hole‐Transport Layer for Inverted Planar MAPbI3 Perovskite Solar Cells

AbstractPolythiophene‐acid‐based conjugated polyelectrolytes have shown great potential as hole‐transport materials for the fabrication of inverted planar perovskite devices with decent power conversion efficiencies (PCEs), benefiting from their tunable structure and functional properties. In contrast to the current progress mainly from side functional group modification, here a simple and effective strategy is reported to effectively regulate the aggregation of P3CT‐K through the modification of the thiophene units in the main chain. A small molecule tris(pentafluorophenyl)borane (TPB) is applied as the Lewis acid to interact with the thiophene unit of polythiophene chain and regulate the aggregation of conjugated polyelectrolytes. The control of aggregation of P3CT‐K not only elevates the hole mobility of P3CT‐K, but also suppresses charge recombination in P3CT‐K composite films. Consequently, the high efficiency of inverted MAPbI3 perovskite solar cells is achieved with a peak power conversion efficiency of 20.7% and simultaneously improved short‐circuit current density and fill factor. This work provides an effective method for the aggregation control of the polyelectrolyte hole materials to promote the performance of inverted planar perovskite solar cells.

Correlating crystalline structure with charge mobility in conjugated statistical copolymers for field-effect transistors

Since thiophene and selenophene have comparable molecular structures and possess individual remarkable optoelectronic characteristics, crystals comprising both units may exhibit improved charge mobility than their respective homopolymers due to the synergy. This, however, has yet to be largely utilized in statistical copolymers. In this study, a series of poly(3-butylthiophene)-stat-poly(3-hexylselenophene) (P3BT-stat-P3HS) statistical copolymers with variable molar ratios of thiophene to selenophene were synthesized and investigated in respect of thermal, crystalline, and charge transport properties. All three P3BT-stat-P3HS copolymers were found to well crystallize in an edge-on configuration in spite of their random arrangement of thiophene and selenophene units along the main backbones. Consequently, high-performance organic field-effect transistors (OFETs) were achieved in as-cast P3BT-stat-P3HS crystals, surpassing those of P3BT, P3HS and P3BT/P3HS blend. After 150 °C thermal annealing, the charge mobilities of these statistical copolymers were further slightly enhanced due to the improved crystallinities as well as more ordered crystalline structures. This work shows the improved field-effect mobilities in conjugated polymer-based statistical copolymers due to the synergy of thiophene and selenophene units. Such P3BT-stat-P3HS crystals may be used in diverse printable flexible electronics owing to their excellent charge mobilities and annealing-free properties.

New 3-Ethynylaryl Coumarin-Based Dyes for DSSC Applications: Synthesis, Spectroscopic Properties, and Theoretical Calculations.

A set of 3-ethynylaryl coumarin dyes with mono, bithiophenes and the fused variant, thieno [3,2-b] thiophene, as well as an alkylated benzotriazole unit were prepared and tested for dye-sensitized solar cells (DSSCs). For comparison purposes, the variation of the substitution pattern at the coumarin unit was analyzed with the natural product 6,7-dihydroxycoumarin (Esculetin) as well as 5,7-dihydroxycomarin in the case of the bithiophene dye. Crucial steps for extension of the conjugated system involved Sonogashira reaction yielding highly fluorescent molecules. Spectroscopic characterization showed that the extension of conjugation via the alkynyl bridge resulted in a strong red-shift of absorption and emission spectra (in solution) of approximately 73–79 nm and 52–89 nm, respectively, relative to 6,7-dimethoxy-4-methylcoumarin (λabs = 341 nm and λem = 410 nm). Theoretical density functional theory (DFT) calculations show that the Lowest Unoccupied Molecular Orbital (LUMO) is mostly centered in the cyanoacrylic anchor unit, corroborating the high intramolecular charge transfer (ICT) character of the electronic transition. Photovoltaic performance evaluation reveals that the thieno [3,2-b] thiophene unit present in dye 8 leads to the best sensitizer of the set, with a conversion efficiency (η = 2.00%), best VOC (367 mV) and second best Jsc (9.28 mA·cm−2), surpassed only by dye 9b (Jsc = 10.19 mA·cm−2). This high photocurrent value can be attributed to increased donor ability of the 5,7-dimethoxy unit when compared to the 6,7 equivalent (9b).

Dopant-free hole transporting polymeric materials based on pyrroloindacenodithiophene donor unit for efficient perovskite solar cells

The hole transporting materials (HTMs) have been extensively studied since the HTMs play a critical role in promoting charge extraction/transport and reducing charge recombination between the perovskite layer and the top metal electrode, thus improving the device power conversion efficiency (PCE). In this study, novel polymeric HTMs with pentacyclic pyrroloindacenodithiophene (NIDT) as an electron-rich unit, and electron-deficient benzotriazole (BTA) as an acceptor, labelled as SGT-512 and SGT-513, were designed and synthesized. To regulate the electron withdrawing ability of the acceptor part, two thiophene units were introduced to the BTA moiety as an acceptor, yielding SGT-513 with a slightly raised HOMO energy level. The alkyl side-chain was introduced to the fused BTA unit to improve the solubility and regulate the morphology and stacking behavior of HTM. Meanwhile, for the donor part, the replacement of the bridging heteroatom in indacenodithiophene with the more electron donating nitrogen atom, helped to promote molecular orbital hybridization leading to a narrower bandgap polymer. The combination of the features of the NIDT donor and BTA acceptor enabled the production of the D-A type polymeric HTM SGT-512 with a high intrinsic hole mobility of 3.8 × 10−4 cm2V−1s−1, a suitable HOMO energy level (−5.25 eV) corresponding to the valence band of the perovskite layer, and excellent film-formation ability. Therefore, the PrSCs based on dopant-free SGT-512 showed a high PCE of 15.57%, which is much higher than that of the control device based on dopant free-P3HT, with a PCE of 13.52%.

Molecular Structure‐Property Relationships of the Asymmetric Thienoacenes: Naphtho[2,3‐b]thieno[2,3‐d]thiophene, Anthra[2,3‐b]thieno[2,3‐d]thiophene, and their Thienyl Derivatives

AbstractPolycyclic aromatic compounds are attractive candidates for organic semiconductor materials whose optical and charge transport properties are significantly influenced by the molecular and packing structures. In this work, we investigated the crystal structure and physical properties of asymmetric bent‐shaped thienoacenes, which have a thieno[3,2‐b]thiophene unit at the end of the fused aromatic ring core, and their thienyl extended‐type derivatives. Among the naphthalene‐based analogs, naphtho[2,3‐b]thieno[2,3‐d]thiophene and its thienyl derivative gave an antiparallel slip‐stack structure. In contrast, among the anthracene‐based analogs, anthra[2,3‐b]thieno[2,3‐d]thiophene produced an antiparallel slip‐stack structure, while its thienyl derivative gave a layered structure with a large molecular orbital overlap. In extended conjugated systems, molecular symmetry of the long axis and dispersion forces were improved, resulting in the formation of crystal structures with large intermolecular interactions. These results suggest the importance of both the extension and molecular symmetry of a conjugated system to controlling the molecular structure.

Synergistic Engineering of Substituents and Backbones on Donor Polymers: Toward Terpolymer Design of High-Performance Polymer Solar Cells.

Design of terpolymers via copolymerization has emerged as a potential strategy for expanding the family of high-performing donor polymers and boosting the photovoltaic performance of non-fullerene polymer solar cells (PSCs). Herein, double-ester-substituted thiophenes and thienothiophenes are incorporated as third building blocks into the donor polymer PBDB-TF, developing two groups of terpolymers with donor-acceptor 1-donor-acceptor 2 (D-A1-D-A2)-type backbones. An optimum 10% concentration of double-ester-substituted thiophene units in PBDB-TF-T10 downshifts the molecular energy and increases the dielectric constant, and delivers proper miscibility and nanostructure in blends with the high-performing acceptor Y6. These characteristics are designed to synergistically enhance the photovoltage, photocurrent, and efficiency of PSCs. The resulting power conversion efficiency (PCE) of 16.4% surpasses the conventional PBDB-TF/Y6 PSCs, and it is among the best-performing PSCs based on PBDB-TF-derived terpolymers. Gratifyingly, PBDB-TF-T10 does not show significant batch-to-batch variation and it retains high PCEs above 16% in a broad range of molecular weights. This work introduces a facile strategy to easily synthesize terpolymers in combination with Y6 for the attainment of high-performing and reproducible non-fullerene PSCs.