Novel Donor–Acceptor Polymer Containing 4,7‐Bis(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole for Polymer Solar Cells with Power Conversion Efficiency of 6.21%

In order to improve the solution processability of 4,7‐bis(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (DTBT)‐based polymers, novel donor–acceptor polymer PTOBDTDTBT containing DTBT and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) with conjugated side chain is designed and synthesized with narrow band gap 1.67 eV and low lying HOMO energy level −5.4 eV. The blend film of PTOBDTDTBT and PC₇₁BM exhibits uniform and smooth film with root‐mean‐square (RMS) surface roughness 1.15 nm because of the excellent solubility of PTOBDTDTBT when six octyloxy side chains are introduced. The hole mobility of the blend film is measured to be 4.4 × 10⁻⁵ cm² V⁻¹s⁻¹ by the space‐charge‐limited current (SCLC) model. The optimized polymer solar cells (PSCs) based on PTOBDTDTBT /PC₇₁BM exhibits an improved PCE of 6.21% with V_oc = 0.80 V, J_sc = 11.94 mA cm⁻² and FF = 65.10%, one of the highest PCE in DTBT containing polymers.

     

Synergetic Evolution of Diketopyrrolopyrrole‐Based Polymeric Semiconductor for High Reproducibility and Performance: Random Copolymerization of Similarly Shaped Building Blocks

A new random copolymer consisting of similarly shaped donor–acceptor building blocks of diketopyrrolopyrrole‐selenophene‐vinylene‐selenophene (DPP‐SVS) and DPP‐thiophene‐vinylene‐thiophene (DPP‐TVT) is designed and synthesized. The resulting P‐DPP‐SVS(5)‐TVT(5) with an equal molecular ratio of the two building blocks produced significantly enhanced solubility when compared to that of the two homopolymers, PDPP‐SVS and PDPP‐TVT. More importantly, despite the maximum segmental randomness of the PDPP‐SVS(5)‐TVT(5) copolymer, its crystalline perfectness and preferential orientation are outstanding, even similar to those of the homopolymers thanks to the similarity of the two building blocks. This unique property produces a high charge carrier mobility of 1.23 cm² V⁻¹ s⁻¹ of PDPP‐SVS(5)‐TVT(5), as determined from polymer field‐effect transistor (PFET) measurements. The high solubility of PDPP‐SVS(5)‐TVT(5) promotes formulation of high‐viscosity solutions which could be successfully processed to fabricate large‐areal PFETs onto hydrophobically treated 4 in. wafers. A total of 269 individual PFETs are fabricated. These devices exhibit extremely narrow device‐to‐device deviations without a single failure and demonstrate an average charge carrier mobility of 0.66 cm² V⁻¹ s⁻¹ with a standard deviation of 0.064. This is the first study to report on successfully realizing large‐areal reproducibility of high‐mobility polymeric semiconductors.

     

High‐Efficiency Large‐Bandgap Material for Polymer Solar Cells

High‐molecular‐weight conjugated polymer HD‐PDFC‐DTBT with N‐(2‐hexyldecyl)‐3,6‐difluorocarbazole as the donor unit, 5,6‐bis(octyloxy)benzothiadiazole as the acceptor unit, and thiophene as the spacer is synthesized by Suzuki polycondensation. HD‐PDFC‐DTBT shows a large bandgap of 1.96 eV and a high hole mobility of 0.16 cm² V⁻¹ s⁻¹. HD‐PDFC‐DTBT:PC₇₁BM‐based inverted polymer solar cells (PSCs) give a power conversion efficiency (PCE) of 7.39% with a V_oc of 0.93 V, a J_sc of 14.11 mA cm⁻², and an FF of 0.56.

     

Alkylphenyl Substituted Naphthodithiophene: A New Building Unit with Conjugated Side Chains for Semiconducting Materials

In this article, a versatile 2‐D conjugated polymer, PNDTP‐DPP, containing alkylphenyl substituted naphthodithiophene is synthesized and characterized. PNDTP‐DPP exhibits good solubility and crystallinity with a π−π stacking distance of ≈3.7 Å. Investigation of polymer solar cells (PSCs) and organic field‐effect transistors (OFET) demonstrates a promising power conversion efficiency (PCE) of 4.11% and a high hole mobility of up to 0.86 cm² V^–1 s^–1, so this is one of the few examples of versatile polymers that show both good field‐effect mobility and PCE.

     

Aromatic Heterocycle 1,3,4‐Oxadiazole‐Substituted Thieno[3,4‐b]thiophene to Build Low‐Bandgap Polymer for Photovoltaic Application

Electron‐deficient heterocycle 1,3,4‐oxadiazole is first introduced to the 2‐position of thieno[3,4‐b]thiophene (TT) to construct a new building block 2‐(thieno[3,4‐b]thiophen‐2‐yl)‐5‐(alkylthio)‐1,3,4‐oxadiazole (TTSO) with alkylthio chain. The polymer PBDT–TTSO based on TTSO and benzodithiophene (BDT) exhibits a deep lying highest occupied molecular orbital (HOMO) energy level of −5.32 eV and low‐bandgap of 1.62 eV. The power conversion efficiency (PCE) of 5.86% is obtained with a relatively high V _OC of 0.74 V, a J _SC of 13.1 mA cm⁻², and FF of 60.5%. Furthermore, as S atom in thioether can be oxidized easily, the optoelectronic properties of PBDT–TTSO treated with different oxidants are preliminary investigated. Interestingly, the oxidation products still maintain high PCE with reduction less than 30%. This work demonstrates a new method to regulate HOMO energy levels by introducing electron‐deficient aromatic heterocyclic moiety.

     

D–π–A–π–A Strategy to Design Benzothiadiazole–carbazole‐based Conjugated Polymer with High Solar Cell Voltage and Enhanced Photocurrent

The theoretical calculations are used to find that D–π–A–π–A style conjugated polymer PC‐TBTBT is more efficient for solar cells application than the D–π–A analog PC‐TBT because the D–π–A–π–A structure has a narrower band gap and higher molar absorption coefficient and redshift spectrum. Motivated by the theoretical prediction, 5,6‐bis(octyloxy)‐2,1,3‐benzothiadiazole and 2,7‐carbazole are adopted to synthesize the D–π–A–π–A style PC‐TBTBT (M_w = 31.1 kDa) and D–π–A analog PC‐TBT (M_w = 87.5 kDa) by Suzuki coupling reaction. Experimental results confirm that D–π–A–π–A PC‐TBTBT ‐based solar cell shows a power conversion efficiency (PCE) of 4.74% with high V_OC of 0.99 V and enhanced J_SC of 9.70 mA cm⁻². The PCE and J_SC achieve improvements of 17% and 26%, respectively, compared to the D–π–A PC‐TBT ‐based solar cell.

     

Planar Conjugated Polymers Containing 9,10‐Disubstituted Phenanthrene Units for Efficient Polymer Solar Cells

Four novel conjugated polymers ( P1‐4 ) with 9,10‐disubstituted phenanthrene (PhA) as the donor unit and 5,6‐bis(octyloxy)benzothiadiazole as the acceptor unit are synthesized and characterized. These polymers are of medium bandgaps (2.0 eV), low‐lying HOMO energy levels (below −5.3 eV), and high hole mobilities (in the range of 3.6 × 10⁻³ to 0.02 cm² V⁻¹ s⁻¹). Bulk heterojunction (BHJ) polymer solar cells (PSCs) with P1‐4 :PC₇₁BM blends as the active layer and an alcohol‐soluble fullerene derivative (FN‐C60) as the interfacial layer between the active layer and cathode give the best power conversion efficiency (PCE) of 4.24%, indicating that 9,10‐disubstituted PhA are potential donor materials for high‐efficiency BHJ PSCs.

     

Evidence for the Chain‐Growth Synthesis of Statistical π‐Conjugated Donor–Acceptor Copolymers

The synthesis of a series of dithienosilole–benzotriazole donor–acceptor statistical copolymers with various donor–acceptor ratios is reported, prepared by Kumada catalyst‐transfer polymerization. Statistical copolymer structure is verified by ¹H NMR and optical absorption spectroscopy, and supported by density functional theory (DFT) calculations. The copolymers exhibit a single optical absorption band that lies between dithienosilole and benzotriazole homopolymers, which shifts with varying donor–acceptor content. A chain extension experiment using a partially consumed benzotriazole solution as a macroinitiator followed by addition of dithienosilole leads to the synthesis of a statistical dithienosilole–benzotriazole block copolymer from a pure benzotriazole block, demonstrating that both chain extension and simultaneous monomer incorporation are possible using this methodology.

     

Single‐Chain Self‐Folding of Synthetic Polymers Induced by Metal–Ligand Complexation

The controlled folding of a single polymer chain is for the first time realized by metal‐ complexation. α,ω‐Bromine functional linear polymers are prepared via activators regenerated by electron transfer (ARGET) ATRP (_,SEC = 5900 g mol⁻¹, Đ = 1.07 and 12 000 g mol⁻¹, Đ = 1.06) and the end groups of the polymers are subsequently converted to azide functionalities. A copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction is carried out in the presence of a novel triphenylphosphine ligand and the polymers to afford homotelechelic bis‐triphenylphosphine polymeric‐macroligands (MLs) (_,SEC = 6600 g mol⁻¹, Đ = 1.07, and 12 800 g mol⁻¹, Đ = 1.06). Single‐chain metal complexes (SCMCs) are formed in the presence of Pd(II) ions in highly diluted solution at ambient temperature. The results derived via ¹H and ³¹P{¹H} NMR experiments, SEC, and DLS unambiguously evidence the efficient formation of SCMCs via metal ligand complexation.

     

Rational Design of High‐Performance Wide‐Bandgap (≈2 eV) Polymer Semiconductors as Electron Donors in Organic Photovoltaics Exhibiting High Open Circuit Voltages (≈1 V)

Systematic optimization of the chemical structure of wide‐bandgap (≈2.0 eV) “donor–acceptor” copolymers consisting of indacenodithiophene or indacenodithieno[3,2‐b ]thiophene as the electron‐rich unit and thieno[3,4‐c ]pyrrole‐4,6‐dione as the electron‐deficient moiety in terms of alkyl side chain engineering and distance of the electron‐rich and electron‐deficient monomers within the repeat unit of the polymer chain results in high‐performance electron donor materials for organic photovoltaics. Specifically, preliminary results demonstrate extremely high open circuit voltages (V _ocs) of ≈1.0 V, reasonable short circuit current density (J _sc) of around 11 mA cm⁻², and moderate fill factors resulting in efficiencies close to 6%. All the devices are fabricated in an inverted architecture with the photoactive layer processed by doctor blade equipment, showing the compatibility with roll‐to‐roll large‐scale manufacturing processes. From the correlation of the chemical structure—optoelectronic properties—photovoltaic performance, a rational guide toward further optimization of the chemical structure in this family of copolymers, has been achieved.

     

Balanced Ambipolar Poly(diketopyrrolopyrrole‐alt‐tetrafluorobenzene) Semiconducting Polymers Synthesized via Direct Arylation Polymerization

The synthesis of an ambipolar π‐conjugated copolymer consisting of alternating diketopyrrolopyrrole and tetrafluorobenzene via direct arylation polymerization (DAP) is reported. Two different combinations of monomers are investigated under various catalytic conditions for DAP. The target polymer obtained under an optimized catalytic condition shows minimal structural defects, a number‐average molecular weight of 33.2 kDa, and balanced electron and hole mobility of 1 × 10⁻² cm² V⁻¹ S⁻¹ in the organic field‐effect transistors fabricated and tested under ambient conditions.

     

Solution‐Processable Donor–Acceptor Polymers with Modular Electronic Properties and Very Narrow Bandgaps

Bridgehead imine‐substituted cyclopentadithiophene structural units, in combination with highly electronegative acceptors that exhibit progressively delocalized π‐systems, afford donor–acceptor (DA) conjugated polymers with broad absorption profiles that span technologically relevant wavelength (λ) ranges from 0.7 < λ < 3.2 μm. A joint theoretical and experimental study demonstrates that the presence of the cross‐conjugated substituent at the donor bridgehead position results in the capability to fine‐tune structural and electronic properties so as to achieve very narrow optical bandgaps (E_g^opt < 0.5 eV). This strategy affords modular DA copolymers with broad‐ and long‐wavelength light absorption in the infrared and materials with some of the narrowest bandgaps reported to date.

     

Recent Advances in Metal‐Containing Polymer Hydrogels

Metal‐containing polymer hydrogels have attracted increasing interest in recent years due to their outstanding properties such as biocompatibility, recoverability, self‐healing, and/or redox activity. In this short review, methods for the preparation of metal‐containing polymer hydrogels are introduced and an overview of these hydrogels with various functionalities is given. It is hoped that this short update can stimulate innovative ideas to promote the research of metal‐containing hydrogels in the communities.

     

Branched 1,2,3‐Triazolium‐Functionalized Polyacetylene with Enhanced Conductivity

Metathesis cyclopolymerization of mono‐ or bissubstituted 1,6‐heptadiynes is undergone to generate the ionic polyacetylenes (iPAs) with branched 1,2,3‐ttriazolium pendants, which possess relatively high intrinsic ionic conductivities of 1.4 × 10⁻⁵–2.1 × 10⁻⁵ S cm⁻¹ at 30 °C. The doping treatment with lithium bis(trifluoromethanesulfonyl)imide endows iPAs with enhanced ionic conductivities of 2.5 × 10⁻⁵–4.3 × 10⁻⁵ S cm⁻¹. Further doping with iodine, iPAs show ionic and electronic dual conductivities of 4.5 × 10⁻⁵–7.1 × 10⁻⁴ and 1.5 × 10⁻⁶–4.5 × 10⁻⁶ S cm⁻¹, respectively. Therefore, the doped iPAs demonstrate the potential in the area of conducting polymers and polymeric electronics.

     

Synthesis of Photocrosslinkable and Amine Containing Multifunctional Nanoparticles via Polymerization‐Induced Self‐Assembly

Photo‐crosslinkable and amine‐containing block copolymer nanoparticles are synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization‐induced self‐assembly of a multifunctional core‐forming monomer, 2‐((3‐(4‐(diethylamino)phenyl)acryloyl)oxy)ethyl methacrylate (DEMA), using poly(2‐hydroxypropyl methacrylate) macromolecular chain transfer agent as a steric stabilizer in methanol at 65 °C. By tuning the chain length of PDEMA, a range of nanoparticle morphologies (sphere, worm, and vesicle) can be obtained. Since cinnamate groups can easily undergo a [2 + 2] cycloaddition of the carbon–carbon double bonds upon UV irradiation, the as‐prepared block copolymer nanoparticles are readily stabilized by photo‐crosslinking to produce anisotropic nanoparticles. The crosslinked block copolymer nanoparticles can be used as templates for in situ formation polymer/gold hybrid nanoparticles.

     

Beyond Donor–Acceptor (D–A) Approach: Structure–Optoelectronic Properties—Organic Photovoltaic Performance Correlation in New D–A1–D–A2 Low‐Bandgap Conjugated Polymers

Low‐bandgap near‐infrared polymers are usually synthesized using the common donor–acceptor (D–A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D–A₁–D–A₂ low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single‐component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D–A₁–D–A₂ polymers as the electron donor mixed with the fullerene derivative [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short‐circuit current densities (J _sc) of around 11 mA cm⁻², high fill factors up to 0.70, and high open‐circuit voltages (V _ocs) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll‐to‐roll large‐scale manufacturing processes.

     

Performance Enhancement of Polymer Solar Cells by Using Two Polymer Donors with Complementary Absorption Spectra

Performance enhancement of polymer solar cells (PSCs) is achieved by expanding the absorption of the active layer of devices. To better match the spectrum of solar radiation, two polymers with different band gaps are used as the donor material to fabricate ternary polymer cells. Ternary blend PSCs exhibit an enhanced short‐circuit current density and open‐circuit voltage in comparison with the corresponding HD‐PDFC‐DTBT (HD)‐ and DT‐PDPPTPT (DPP)‐based binary polymer solar cells, respectively. Ternary PSCs show a power conversion efficiency (PCE) of 6.71%, surpassing the corresponding binary PSCs. This work demonstrates that the fabrication of ternary PSCs by using two polymers with complementary absorption is an effective way to improve the device performance.

     

Tunable AICPL of (S)‐Binaphthyl‐Based Three‐Component Polymers via FRET Mechanism

Five three‐component chiral polymers incorporating (S )‐1,1′‐binaphthyl, tetraphenylethene (TPE) and fluorene moieties are designed and synthesized by Pd‐catalyzed Sonogashira reaction. All these polymers show obvious aggregation induced emission enhancement response behavior in the fluorescence emission region of 460–480 nm. Interestingly, three of them show aggregation‐induced circularly polarized luminescence (AICPL) signals in tetrahydrofuran–H₂O mixtures. Most importantly, these AICPL signals can be tuned by changing the molar ratios of TPE and fluorene components through fluorescence resonance energy transfer and give the highest glum = ±4.0 × 10⁻³. This work provides a novel strategy for developing AICPL‐enhanced materials.

     

Broad Bandgap D–A Copolymer Based on Bithiazole Acceptor Unit for Application in High‐Performance Polymer Solar Cells with Lower Fullerene Content

A new broad bandgap and 2D‐conjugated D‐A copolymer, PBDTBTz‐T , based on bithienyl‐benzodithiophene donor unit and bithiazole (BTz) acceptor unit, is designed and synthesized for the application as donor material in polymer solar cells (PSCs). The polymer possesses highly coplanar and crystalline structure with a higher hole mobility and lower HOMO energy level which is beneficial to achieve higher open circuit voltage (V_oc) of the PSCs with the polymer as donor. The PSCs based on PBDTBTz‐T :PC₇₁BM blend film with a lower PC₇₁BM content of 40% demonstrate a power conversion efficiency (PCE) of 6.09% with a relatively higher V_oc of 0.92 V. These results indicate that the lower HOMO energy level of the BTz‐based D–A copolymer is beneficial to a high V_oc of the PSCs. The polymer, with highly coplanar and crystalline structure, can effectively reduce the content of fullerene acceptor in the active layer and can enhance the absorption and PCE of the PSCs.

     

Single‐Chain Polymer Self‐Assembly Using Complementary Hydrogen Bonding Units

A triblock copolymer containing the complementary hydrogen bonding recognition pair ureidoguanosine–diaminonaphthyridine (UG–DAN) as pendant functional groups is synthesized using ring‐opening metathesis polymerization (ROMP). The norbornene‐based DAN monomer is shown to allow for a controlled polymerization when polymerized in the presence of a modi­fied‐UG molecule that serves as a protecting group, subsequently allowing for the fabrication of functionalized triblock copolymers. The self‐assembly of the copolymers was characterized using dynamic light scattering and ¹H NMR spectroscopy. It is demonstrated that the polymers self‐assemble via complementary hydrogen bonding motifs even at low dilutions, indicating intramolecular interactions.