Donor Acceptor Copolymers Research Articles

Systematic Tuning of 2,1,3-Benzothiadiazole Acceptor Strength by Monofunctionalization with Alkylamine, Thioalkyl, or Alkoxy Groups in Carbazole Donor–Acceptor Polymers

A simple route to the preparation of alkylamine, thioalkyl, and alkoxy monofunctionalized 4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole) based monomers is reported from a common fluorinated precursor. Copolymerization with a carbazole comonomer under Suzuki conditions yielded a series of analogous donor–acceptor copolymers in which the only difference was the nature of the heteroatom (N, O, or S) on the benzothiadiazole core. This was shown to have a significant impact on the wavelength and intensity of the intramolecular charge transfer (ICT) absorption peak due to a combination of electronic and steric factors. Substantial differences were also observed in the solar cell performance of blends with PC71BM, with the octylamino substituted polymer exhibiting significantly lower performance than the other two polymers. This polymer also exhibited a reversible change in the optical spectra upon exposure to acid, suggesting potential as a sensing material.

Novel perylene diimide based polymeric electron-acceptors containing ethynyl as the π-bridge for all-polymer solar cells

We designed and synthesised two n-type donor-acceptor copolymers based on perylenediimide (PDI). These copolymers contained an ethynyl moiety as the π-bridge between PDI and the electron-donating unit of either benzodithiophene (BDT) or fluorine (F), with the corresponding polymers denoted as PPDI-BDT and PPDI-F, respectively. The molecular geometry and the optical and electrochemical properties of the polymers were affected by the electron-donating unit. Both copolymers exhibited relatively broad light-absorption profiles and deep lowest unoccupied molecular orbital energy levels of about −3.8 eV. All-polymer solar cells (all-PSCs) were fabricated using these copolymers as the electron-accepting material and a medium-bandgap conjugated polymer, PBDB-T, as the electron-donating material. The resulting all-PSC based on PPDI-F exhibited a power conversion efficiency of 5.09%, which is significantly higher than that of the device fabricated using PPDI-BDT (2.73%). This improvement was attributed to the higher open-circuit voltage, greater charge carrier mobility and more effective charge transfer of the PBDB-T:PPDI-F blend film. These results suggest that the developed n-type PDI-based copolymers are promising candidates as electron-accepting materials for the construction of high-performance all-polymer solar cells.

Reduced exchange narrowing caused by gate-induced charge carriers in high-mobility donor–acceptor copolymers

Reduced exchange narrowing caused by gate-induced charge carriers in high-mobility donor–acceptor copolymers

Effect of furan π-bridge on the photovoltaic performance of D-A copolymers based on bi(alkylthio-thienyl)benzodithiophene and fluorobenzotriazole

The medium band gap donor-acceptor (D-A) copolymer J61 based on bi(alkylthio-thienyl)benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit and thiophene as π-bridge has demonstrated excellent photovoltaic performance as donor material in nonfullerene polymer solar cells (PSCs) with narrow bandgap n-type organic semiconductor ITIC as acceptor. For studying the effect of π-bridges on the photovoltaic performance of the D-A copolymers, here we synthesized a new D-A copolymer J61-F based on the same donor and acceptor units as J61 but with furan π-bridges instead of thiophene. J61-F possesses a deeper the highest occupied molecular orbital (HOMO) level at −5.45 eV in comparison with that (−5.32 eV) of J61 . The non-fullerene PSCs based on J61-F :ITIC exhibited a maximum power conversion efficiency (PCE) of 8.24% with a higher open-circuit voltage ( V oc) of 0.95 V, which is benefitted from the lower-lying HOMO energy level of J61-F donor material. The results indicate that main chain engineering by changing π-bridges is another effective way to tune the electronic energy levels of the conjugated D-A copolymers for the application as donor materials in non-fullerene PSCs.

Indolo[3,2-b]indole-Containing Donor–Acceptor Copolymers for High-Efficiency Organic Solar Cells

The organic solar cell (OSC) performance of a series of new donor–acceptor copolymers containing indolo[3,2-b]indole as a key donor block and benzothiadiazole (BT) units with various degrees of fluorination as acceptors is reported. Compared with the simple carbazole unit, the strategically developed indolo[3,2-b]indole unit is found to significantly extend π-conjugation and thus increase the intermolecular interactions of the resulting copolymer, as probed by density functional theory calculations, photophysical studies, and structural/morphological analyses. In addition, fluorination of BT can facilitate nanostructuring of the copolymers, mainly due to further planarization of the backbone, which leads to apparently higher hole/electron charge carrier mobilities. The OSC properties of this series of new copolymers blended with fullerene show a strong dependence on the fine and continuous fibrous nanostructure of the blend film. The indolo[3,2-b]indole-based copolymer with singly fluorinated BT units possesses optimal intermolecular interactions and achieves the highest power conversion efficiency of 8.84% under AM 1.5G illumination. This result shows the potential of π-extended carbazole moieties for achieving high-performance OSCs with many of the favorable properties induced by large heteroacene blocks.

Hybrid ZnO-organic semiconductor interfaces in photodetectors: A comparison of two near-infrared donor-acceptor copolymers

Hybrid organic-inorganic photodiode interfaces have gained significant interest due to their unique physical properties such as mechanical flexibility and high photosensitivity. Two diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers with different backbone conformations are characterized in an inverted non-fullerene photodiode architecture using ZnO nano-patterned films as the electron transport layer. The DPP copolymer with a thienothiophene unit (PBDT-TTDPP) is more planar and rigid compared to the DPP system with a thiophene unit connecting the donor and acceptor moieties within the monomer (PBDT-TDPP). The hybrid interfaces were optimized by using poly(3-hexylthiophene) (P3HT) as the p-type layer for monitoring the critical thickness and morphology of the ZnO layer. The maximum photoresponsivity from a P3HT:ZnO photodiode was found to be 56 mA/W. The photoresponsivity of PBDT-TTDPP:ZnO photodiodes were found to be more than two orders of magnitude higher than PBDT-TDPP:ZnO photodiodes, which is attributed to an enhanced transport of carriers due to the planar backbone conformation of the PBDT-TTDPP copolymer. Capacitance-voltage measurements from hybrid Schottky barrier interfaces further shed light into the nature of photocarriers and device parameters. First-principles time-dependent density-functional theoretical calculations yield a higher absorptivity for the PBDT-TTDPP dimer compared to PBDT-TDPP.

Effect of Co-monomers on Triphenylamine-Thiazolothiazole-Based Donor-Acceptor Copolymers: Synthesis and their Optical Properties

Donor-Acceptor type copolymer, poly(9,9-di-n-hexylfluorene-alt-2,5-bis(N,N-diphenylaniline)-thiazolo[5,4-d]thiazole) (P1) and random copolymers of P2-P4 have been synthesized using Suzuki polymerization reaction. For random copolymers, dicyanomethane derivative of triphenylamine, dithienothiophene and thienothiophene were used as co-monomers, respectively to P2-P4 along fluorene and 2,5-bis(N,N-diphenylaniline)-thiazolo[5,4-d]thiazole). Studies on the optical, thermal and electrochemical properties of these copolymers (P1-P4) were carried out. By incorporating different aromatic moiety as co-monomer, optical properties of the polymers were tuned which exhibited significant changes in UV-Vis absorption as well as emission characteristics. All these copolymers were thermally stable upto 300 °C and soluble in common organic solvents. Electrochemical studies of these polymers indicate that they have deep HOMO energy levels. Photoluminescence emission studies of the synthesized polymers as thin film showed that polymer (P2) with dicyanomethane derivative of triphenylamine was red shifted when compared with other polymers. Weight average moleular weights of the polymers were in the range of 6.457 KDa to 12.000 KDa.

Simultaneous Substitution of Silicon and Fluorine Atom on Donor-Acceptor Copolymers for Photovoltaic Applications

To investigate the effect of silole-containing and fluorination on the photovoltaic performance of polymer solar cells, two conjugated donor–acceptor copolymers have been synthesized via Stille coupling reaction. Both donor–acceptor alternating copolymers consisted of 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene as the donor unit and nonfluorinated or fluorinated 2,1,3-benzooxadiazole (BO) as the acceptor unit, along with a thiophene group as the π-bridge between the donor and acceptor unit. For comparison, the copolymer composed of the 4,4-diethylhexyl-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) donor unit and the BO acceptor unit has also been prepared. UV–vis spectra of the three copolymers display a panchromatic absorption ranging from 300 to 1100 nm. The optical band gap obtained from the Tauc relation for the CPDT-containing polymer is 1.54 eV. With regard to the silole-containing copolymers, the optical band gaps for nonfluorinated copolymer and fluorinated copolymer are reduced to 1.46 and 1.42 eV, respectively. In comparison with both nonfluorinated polymers, the photovoltaic performance of fluorinated polymer is significantly improved due to the increased J sc and enhanced V oc. Based on the indium tin oxide (ITO) coated glass/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/polymer:phenyl-C61-butyric acid methyl ester/LiF/Al device structure, the optimal device efficiency obtained from the fluorinated copolymer at room temperature under the illumination of AM 1.5 is 3.74%, with a high V oc up to 0.87 V.

Molecular Doping of a High Mobility Diketopyrrolopyrrole–Dithienylthieno[3,2-b]thiophene Donor–Acceptor Copolymer with F6TCNNQ

Herein we present a molecular doping of a high mobility diketopyrrolopyrrole–dithienylthieno[3,2-b]thiophene donor–acceptor copolymer poly[3,6-(dithiophene-2-yl)-2,5-di(6-dodecyloctadecyl)pyrrolo[3,4-c]pyrrole-1,4-dione-alt-thieno[3,2-b]thiophene], PDPP(6-DO)2TT, with the electron-deficient compound hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ). Despite a slightly negative HOMOdonor–LUMOacceptor offset of −0.12 eV which may suggest a reduced driving force for the charge transfer (CT), a partial charge CT was experimentally observed in PDPP(6-DO)2TT:F6TCNNQ by absorption, vibrational, and electron paramagnetic resonance spectroscopies and predicted by density functional theory calculations. Despite the modest CT, PDPP(6-DO)2TT:F6TCNNQ films possess unexpectedly high conductivities up to 2 S/cm (comparable with the conductivities of the benchmark doped polymer system P3HT:F4TCNQ having a large positive offset). The observation of the high conductivity in doped PDPP(6-DO)2TT films can be explained by a...

Effects of alkoxy substitution on molecular structure, physicochemical and photovoltaic properties of 2D-conjugated polymers based on benzo[1,2-b:4,5-b′]dithiophene and fluorinated benzothiadiazole

Two donor-acceptor (D-A) copolymers (PMT-FBT and PET-FBT) with alkoxythiophene-substituted benzo[1,2-b:4,5-b′]dithiophene as donor unit and difluorobenzothiazole as acceptor unit, were synthesized and employed as donor material for polymer solar cells (PSCs). The comparative study showed that the type (methoxyl versus ethylenedioxyl) and the position (3- and 4-positons) of alkoxy substituents on thiophene side chains have great effects on the molecular geometries and optoelectronic properties of these copolymers. PSCs based on two polymers exhibit maximum power conversion efficiencies of 3.29% and 2.40%, with open-circuit voltage (Voc) values as high as 0.85 and 1.02V for PMT-FBT and PET-FBT, respectively.

Simulation study on the effects of chemical structure and molecular size on the acceptor strength in poly(3-hexylthiophene)-based copolymer with alternating donor and acceptor for photovoltaic applications

This research assessed the effects of various chemical structures and molecular sizes on the simulated geometric parameters, electron structures, and spectroscopic properties of single-chain complex alternating donor–acceptor (D–A) monomers and copolymers that are intended for use as photoactive layer in a polymer solar cell by using Kohn–Sham density functional theory with B3LYP exchange-correlation functional. The 3-hexylthiophene (3HT) was selected for electron donor, while eight chemicals, namely thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT), thiadiazolothieno-pyrazine (TPD), oxadiazole (OXD) and 5-diphenyl-1,2,4-triazole (TAZ), were employed as electron acceptor functional groups. The torsional angle, bridge bond length, intramolecular charge transfer, energy levels, and molecular orbitals were analyzed. The simulation results reveal that the geometry and electron structure of donor–acceptor monomer and copolymer are significantly impacted by heterocyclic rings, heteroatoms, fused rings, degree of steric hindrance and coplanarity of the acceptor molecular structure. Planar conformation was obtained from the D copolymer, and a pseudo-planar structure with the TD copolymer. The TAZ acceptor exhibited strong steric hindrance due to its bulky structure and non-planarity of its structure. An analysis of the electron structures indicated that the degree of intramolecular electron-withdrawing capability had the rank order TAZ < Z < D < TPD < OXD < TP < BT < TD. The TD is indicated as the most effective acceptor among those that were simulated. However, the small energy gaps of TD as well as TPD copolymer indicate that these two copolymers can be used in transparent conducting materials. The copolymer based on BT acceptor exhibited good intramolecular charge transfer and absorbed at 656 nm wavelength which is close to the maximum flux of solar spectrum. Hence, the BT acceptor functional group provides a compromise in the characteristics of a donor–acceptor copolymer, useful in a polymeric candidate material for the photoactive layer in a polymer solar cell.

Effect of side chains on phenanthrene based D-A type copolymers for polymer solar cells

A series of low band gap conjugated copolymers containing 9,10-modified phenanthrene and diketopyrrolopyrrole (DPP) units were synthesized as electron donor materials for bulk heterojunction organic solar cells. These donor-acceptor type PDPP copolymers have varying solubilizing groups on their identical conjugated backbones. The optical bandgap of PDPP copolymers is about 1.6 eV which corresponds to the long wavelength region of the solar spectrum. Through the incorporation of phenanthrene units into the conjugated backbone instead of commonly used thiophene derivatives, a higher open-circuit voltage of about 0.8 V could be achieved, as a result of their deeper HOMO level. Of all the devices, the P4:PC61BM BHJ system showed the best performance with a Voc of 0.79 V, a Jsc of 5.97 mA cm−2, a fill factor of 0.62 and a power conversion efficiency of 2.73% due to superior nanoscale phase separation between the electron donor and electron acceptor materials than in the other polymers arising from short-branched solubilizing groups on the phenanthrene side of its conjugated backbone.

Super-exchange-induced high performance charge transport in donor–acceptor copolymers

Super-exchange-induced charge transport is proposed in donor–acceptor copolymers, and the corresponding design strategy for high mobility polymers is put forward.

High-efficiency perovskite solar cells employing a conjugated donor–acceptor co-polymer as a hole-transporting material

In this work, we have successfully demonstrated that molecularly p-doping of donor–acceptor co-polymer PCPDTBT as an efficient hole-transporting material in perovskite solar cells with a decent power conversion efficiency of 15.1%.

Performance of Donor-Acceptor copolymer materials PCPDTBT and PCDTBT with poly hexyl thiophene polymer in a ternary blend

The efficiency of organic solar cells is limited by the absorbance of the donor and acceptor material in the binary blend. In order to extend the absorption spectrum of the absorbing species, a ternary blend is formed by adding a donor material to the already existing binary blend. In this paper we discuss about the addition of P3HT (Polyhexylthiopene) to either Donor-Acceptor copolymer material PCPDTBT(Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′] di thio phene)-alt-4,7(2,1,3-benzothiadiazole) or PCDTBT (poly [poly [N-9’-heptadecanyl-2.7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole-4,7-diyl-2,5-thio phenediyl) with common acceptor PC60BM (phenyl-C61-butyric acid). Donor-acceptor copolymers are materials with repeated units of electron donor and electron acceptor units connected by a π-conjugated small molecule. Interestingly a decrease in efficiency is observed when P3HT is added to the binary blend of PCDTBT: PCBM and an increase in efficiency is observed when P3HT is added to the binary blend of PCPDTBT: PCBM. There is cascading of energy levels in both the ternary blends PCDTBT: P3HT: PCBM and PCPDTBT: P3HT: PCBM which helps in the movement of free charge carriers. And also the open circuit voltage decreased in both the cases by the addition of P3HT. But the short circuit current density increased in the PCPDTBT: P3HT: PCBM ternary blend due to the improvement in photon absorption. The UV-Vis spectrophotometry, photoluminescence spectrometry, and X-ray diffraction confirm the results.

Synthesis and side-chain isomeric effect of 4,9-/5,10-dialkylated-β-angular-shaped naphthodithiophenes-based donor–acceptor copolymers for polymer solar cells and field-effect transistors

P4,9-βNDTDTFBT:PC71BM-based solar cell device achieves a high PCE of 7.23%.

Design of a thiophene-fused benzotriazole unit as an electron acceptor to build D–A copolymers for polymer solar cells

A new electron-acceptor, thiophene-fused benzotriazole (BTAZT), is designed for the first time to construct donor–acceptor copolymers with bithienyl substituted benzo[1,2-b:4,5-b′]dithiophene (BDTT) as an electron-donor unit for polymer solar cells (PSCs).

High photovoltaic performance of as-cast devices based on new quinoxaline-based donor–acceptor copolymers

Two new quinoxaline-based copolymers with different alkylthio side chains show high photovoltaic performance in as-cast devices.

Ambipolar tetrafluorodiphenylethene-based donor–acceptor copolymers: synthesis, properties, backbone conformation and fluorine-induced conformational locks

Tetrafluorodiphenylethene-based donor–acceptor copolymers with multiple conformational locks exhibit excellent ambipolar charge carrier transport characteristics.

Novel vinylene-bridged donor–acceptor copolymers: synthesis, characterization, properties and effect of cyano substitution

Cyano groups were introduced into two vinylene-bridged monomers and four polymers were synthesized, and their FET performances were fully studied.