Non-fused Nonfullerene Acceptors with an Asymmetric Benzo[1,2-b:3,4-b', 6,5-b"]trithiophene (BTT) Donor Core and Different AcceptorTerminal Units for Organic Solar Cells

Here in, we have designed two new unfused non-fullerene small molecules using asymmetric benzo[1,2-b:3.4-b', 6,5-b"]trithiophene (BTT) as the central donor core and different terminal units i. e., 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (NFA-4) and 1,3-diethyl-2-thioxodi hydropyrimidine-4,6 (1H,5H)-dione (NFA-5) and examined their optical and electrochemical properties. Using a wide band-gap copolymer D18, organic solar cells (OSCs) based on bulk heterojunction of D18:NFA-4 and D18:NFA-5 showed overall power conversion efficiency (PCE) of about 17.07 % and 11.27 %, respectively. The increased PCE for the NFA-4-based OSC, compared to NFA-5 counterpart, is due higher value of short circuit current (JSC), open circuit voltage (VOC), and fill factor (FF). Following the addition of small amount of NFA-5 to the binary bulk heterojunction D18:NFA-4, the ternary organic solar cells attained a PCE of 18.05 %, surpassing that of the binary counterparts due to the higher values of which is higher than that for the binary counterparts and attributed to the increased values of JSC, FF, and VOC. The higher value of JSC is linked to the efficient use to excitons transferred from NFA-5 to NFA-4 with a greated dipole moment than NFA-5 and subsequently dissociated into a free charge carrier efficiently.

Morphology Driven by Molecular Structure of Thiazole-Based Polymers for Use in Field-Effect Transistors and Solar Cells

The effects of the molecular structure of thiazole-based polymers on the active layer morphologies and performances of electronic and photovoltaic devices were studied. Thus, thiazole-based conjugated polymers with a novel thiazole-vinylene-thiazole (TzVTz) structure were designed and synthesized. The TzVTz structure was introduced to extend the π conjugation and coplanarity of the polymer chains. By combining alkylthienyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT) or dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DTBDT) electron-donating units and a TzVTz electron-accepting unit, enhanced intermolecular interactions and charge transport were obtained in the novel polymers BDT-TzVTz and DTBDT-TzVTz. With a view to using the polymers in transistor and photovoltaic applications, the molecular self-assembly in and their nanoscale morphologies of the active layers were controlled by thermal annealing to enhance the molecular packing and by introducing a diphenyl ether solvent additive to improve the miscibility between polymer donors and [6,6]phenyl-C71-butyric acid methyl ester (PC₇₁ BM) acceptors, respectively. The morphological characterization of the photoactive layers showed that a higher degree of π-electron delocalization and more favorable molecular packing in DTBDT-TzVTz compared with in BDT-TzVTz leads to distinctly higher performances in transistor and photovoltaic devices. The superior performance of a photovoltaic device incorporating DTBDT-TzVTz was achieved through the superior miscibility of DTBDT-TzVTz with PC₇₁ BM and the improved crystallinity of DTBDT-TzVTz in the nanofibrillar structure.

Synthesis of unsymmetrical benzotrichalcogenophenes by N-heterocyclic carbene-palladium-catalyzed intramolecular direct C3-arylation of chalcogenophenes

A series of new unsymmetrical benzotrichalcogenophenes (BTCs) were synthesized by the Pd-N-heterocyclic carbene catalyzed intramolecular C3-arylation of furan, thiophene, selenophene and tellurophene units. This is the first time that a C3-direct arylation of selenophene and tellurophene moieties has ever been demonstrated.

Bithiazole: An Intriguing Electron-Deficient Building for Plastic Electronic Applications

The heterocyclic thiazole unit has been extensively used as electron-deficient building block in π-conjugated materials over the last decade. Its incorporation into organic semiconducting materials is particularly interesting due to its structural resemblance to the more commonly used thiophene building block, thus allowing the optoelectronic properties of a material to be tuned without significantly perturbing its molecular structure. Here, we discuss the structural differences between thiazole- and thiophene-based organic semiconductors, and the effects on the physical properties of the materials. An overview of thiazole-based polymers is provided, which have emerged over the past decade for organic electronic applications and it is discussed how the incorporation of thiazole has affected the device performance of organic solar cells and organic field-effect transistors. Finally, in conclusion, an outlook is presented on how thiazole-based polymers can be incorporated into all-electron deficient polymers in order to obtain high-performance acceptor polymers for use in bulk-heterojunction solar cells and as organic field-effect transistors. Computational methods are used to discuss some newly designed acceptor building blocks that have the potential to be polymerized with a fused bithiazole moiety, hence propelling the advancement of air-stable n-type organic semiconductors.

Dithieno[3,2-b:2',3'-d]pyridin-5(4H)-one based D-A type copolymers with wide bandgaps of up to 2.05 eV to achieve solar cell efficiencies of up to 7.33

A PCE of 7.33% was achieved in a PSC based on a new copolymer, PDTPO-IDT, with bandgaps of up to 2.05 eV.

Two new polymers, PDTPO-IDT and PDTPO-IDTT, are synthesized through copolymerization of 4-(2-octyldodecyl)-dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one (DTPO) with indacenodithiophene (IDT) or indacenodithieno[3,2-b]thiophene (IDTT). The rational combination of the planar DTPO unit with ladder-type IDT and IDTT units endows the resulting copolymers with wide optical bandgaps of ca. 2.05 eV, low HOMO energy levels of ca. –5.32 eV and good hole-transporting abilities with a hole mobility of 1.0 × 10^–3 cm² V^–1 s^–1. The polymer solar cell (PSC) in a conventional structure based on PDTPO-IDT as donor and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as acceptor achieves a high power conversion efficiency (PCE) of up to 7.33%, the highest value for PSCs based on polymers with optical bandgap over 2.0 eV to date, along with a remarkable open-circuit voltage (V_oc) approaching 0.97 V. The performance of the PDTPO-IDTT based PSC is slightly behind this with a moderate PCE of 5.47% under the same conditions. The relationship between the copolymer structures and optoelectronic properties as well as photovoltaic performance are comprehensively investigated by experiments and theoretical simulations.

Structures and photoelectric properties of five benzotrithiophene isomers-based donor-acceptor copolymers

In this paper, we have investigated the structures, electronic and optical properties of five conjugated copolymers (BTT1-BTz, BTT2-BTz, BTT3-BTz, BTT4-BTz and BTT5-BTz) featuring benzotrithiophene (BTT) isomers as donor units and benzothiadiazole (BTz) as acceptor units, linked through thiophene spacers, employing many-body perturbation theory (MBPT). We have explored the isomer effects by configuration of the sulfur atoms in BTT units, aimed to get insight into how the structural modifications to the conjugated backbone can influence the molecular structures and electronic properties of conjugated polymers. Using the trimer as the computational model, the calculated low and high energy absorption bands (660 and 413 nm) for BTT1-BTz agree well with the experimental ones (645 and 430 nm) with a small offset of ~15 nm. On the basis of our calculations, it is found that the backbones of these polymers display different coplanarities, with the dihedral angles between the two neighboring rings varying from 12.3° to 79.0°. Importantly, both BTT1-BTz and BTT2-BTz exhibit intense adsorption around 660 and 623 nm, indicating their promising application in solar cells, whereas BTT3-BTz and BTT4-BTz display the intense adsorption at 569 and 551 nm, which are also usable in the tandem solar cells. BTT5-BTz has narrow and weak adsorption in the visible and infrared region, implying it is not conducive to the sunlight absorption. The blue shift of about 150 nm from BTT1-BTz to BTT5-BTz is suggested to be originated from the shorter effective conjugation lengths.

Simultaneous enhancement of performance and insensitivity to active layer thickness for OPVs by functionalizing π-spacer's side chain

A novel BTI based copolymer was designed by incorporating a decylthio modified π-spacer into the backbone for improving the photovoltaic performance.

N. A, B. H. Rational design of benzodithiophene based conjugated polymers for better solar cell performance

We present a concise review of conjugated polymers based on benzodithiophenes (BDTs) for high-performance polymer solar cells (PSCs).

Conjugated foldamers with unusually high space-charge-limited current hole mobilities

Charge carrier mobility and its optimization play a critical role in the development of cutting-edge organic electronic and optoelectronic devices. Even though space-charge-limited current (SCLC) hole mobilities as high as 1.4 cm(2) V(-1) s(-1) have been reported for microscopically sized highly ordered liquid-crystalline conjugated small molecules, the SCLC hole mobility of device-sized thin films of conjugated polymers is still much lower, ranging from 10(-6) to 10(-3) cm(2) V(-1) s(-1). Herein, we report the synthesis, characterizations, and thin-film SCLC mobility of three discotic conjugated polymers, INDT-TT, INDT-BT, and INDT-NDT. Optical studies indicate that polymer INDT-NDT adopts a folded conformation in solutions of good or poor solvents, whereas polymer INDT-TT stays as random monomeric chains in good solvents and interchain aggregates in poor solvents. INDT-BT polymer chains, however, stay as foldamers in dilute solutions of good solvents but interchain aggregates in concentrated solutions or poor solvents. Circular dichroism spectroscopy provides clear evidence for the helical folding of INDT-NDT in solutions. Thin films spin-coated from 1,2-dichlorobenzene solutions of the polymers show SCLC hole mobility of 2.20 × 10(-6), 8.79 × 10(-5), and 2.77 × 10(-2) cm(2) V(-1) s(-1) for INDT-TT, INDT-BT, and INDT-NDT, respectively. HRTEM and powder XRD measurements show that INDT-NDT pristine thin films contain nanocrystalline domains, whereas the INDT-TT and INDT-BT films are amorphous. Thin films of INDT-NDT:PC71BM blends show increased crystallinity and further improved SCLC hole mobility up to 1.29 × 10(-1) cm(2) V(-1) s(-1), one of the highest SCLC mobility values ever recorded on solution-processed organic semiconducting thin films. The persistent folding conformation of INDT-NDT is believed to be responsible for the high crystallinity of its thin films and its high SCLC mobilities.

Novel solution-processible small molecules based on benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene for effective organic photovoltaics with high open-circuit voltage

Two novel A–D–A small molecules D1 and D2, containing benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene as the central electron-donating unit and two thiophenes or three thiophenes as conjugated π-bridges, were designed and synthesized.

Synthesis and photovoltaic properties of new donor–acceptor (D–A) copolymers based on benzo[1,2-b:3,4-b′:6,5-b′′] trithiophene donor and different acceptor units (P1 and P2)

A power conversion efficiency of about 5.26% has been achieved for the device based onP1:PC71BM.

Fluorinated low band gap copolymer based on dithienosilole–benzothiadiazole for high-performance photovoltaic device

The introduction of fluorine atom into a copolymer of dithienosilole–benzothiadiazole causes significant enhancement in the PSCs with the PCE increasing from 4.68% to 6.70%.

High-crystalline medium-band-gap polymers consisting of benzodithiophene and benzotriazole derivatives for organic photovoltaic cells

Two semiconducting conjugated polymers were synthesized via Stille polymerization. The structures combined unsubstituted or (triisopropylsilyl)ethynyl (TIPS)-substituted 2,6-bis(trimethylstannyl)benzo[1,2-b:4.5-b']dithiophene (BDT) as a donor unit and benzotriazole with a symmetrically branched alkyl side chain (DTBTz) as an acceptor unit. We investigated the effects of the different BDT moieties on the optical, electrochemical, and photovoltaic properties of the polymers and the film crystallinities and carrier mobilities. The optical-band-gap energies were measured to be 1.97 and 1.95 eV for PBDT-DTBTz and PTIPSBDT-DTBTz, respectively. Bulk heterojunction photovoltaic devices were fabricated and power conversion efficiencies of 5.5% and 2.9% were found for the PTIPSBDT-DTBTz- and PBDT-DTBTz-based devices, respectively. This difference was explained by the more optimal morphology and higher carrier mobility in the PTIPSBDT-DTBTz-based devices. This work demonstrates that, under the appropriate processing conditions, TIPS groups can change the molecular ordering and lower the highest occupied molecular orbital level, providing the potential for improved solar cell performance.

Rational design of benzotrithiophene-diketopyrrolopyrrole-containing donor-acceptor polymers for improved charge carrier transport

Two new donor-acceptor polymers containing benzo[2,1-b:3,4-b':5,6-c'']trithiophene (BTT) as donor and diketopyrrolopyrrole (DPP) as acceptor are synthesized and applied in OFETs. By tuning the alkyl substituents of the polymers, a striking difference in packing order, thin-film arrangement, and charge carrier transport is observed. The polymer without substituents at the BTT exhibits a hole mobility two orders of magnitude higher than that with alkyl chains therein.