A Novel n-Type Conjugated Polymer DOCN-PPV: Synthesis, Optical, and Electrochemical Properties

A Novel n-Type Conjugated Polymer DOCN-PPV:  Synthesis, Optical, and Electrochemical Propertie

Synthesis and Characterization of New Low-Bandgap Diketopyrrolopyrrole-Based Copolymers

Eleven new low bandgap diketopyrrolopyrrole-based copolymers have been prepared by Suzuki or Stille cross-coupling polycondensation reactions. Comonomers derived from thiophene, carbazoles, fluorene, dibenzosilole, and dithienylsilole have been investigated. The structural, thermal, optical, and electrochemical properties of all resulting copolymers have been characterized. These copolymers exhibit broad absorption extending into the near-infrared region with absorption maxima near 640−710 nm and optical band gaps ranging from 1.2 to 1.6 eV. HOMO energy levels of the copolymers vary between −5.6 and −5.2 eV whereas the LUMO energy levels are pinned between −3.9 and −3.8 eV. The combination of extending absorption into near-infrared region, optimal energy levels, and excellent mechanical and thermal properties makes this class of low bandgap copolymers very promising for photovoltaic applications

Indene Addition of [6,6]-Phenyl-C₆₁-butyric Acid Methyl Ester for High-Performance Acceptor in Polymer Solar Cells

Indene addition product of [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM), indene-PC60BM (IPC60BM), was synthesized by a one-pot reaction of indene and PC60BM at 180 °C for 12 h, for combining the advantages of PC60BM and indene-C60 bis-adduct in the application as acceptor in polymer solar cells (PSCs). The lowest unoccupied molecular orbital (LUMO) energy level of IPC60BM is 0.12 eV up-shifted than that of PC60BM. The PSC based on poly(3-hexylthiophene) (P3HT) as donor and IPC60BM as acceptor shows a higher Voc of 0.72 V and higher power conversion efficiency (PCE) of 4.39% under the illumination of AM1.5G, 100 mW/cm2, while the PSC based on P3HT/PC60BM displays Voc of 0.58 V and PCE of 3.49% only. The results indicate that IPC60BM is a better acceptor than PC60BM for the P3HT-based PSCs and could be a promising new acceptor instead of PC60BM for high-performance PSCs

Observation of an Exciton-Plasma Transition in a Molecular Semiconductor

The nonfullerene electron acceptors (NFAs) for organic solar cells are attracting intense research efforts due to their impressive performance. Understanding the temporal evolution of the excited states in NFAs is essential to gain insights into the working mechanism of these state-of-the-art devices. Here we characterized the photoconductivities of a neat Y6 film and a Y6:PM6 blend film using time-resolved terahertz spectroscopy. Three different types of excited states were identified based on their distinct terahertz responses, i.e., plasma-like carriers, weakly bound excitons, and spatially separated carriers. Under high-intensity excitation, the many-body interaction of excitons in the Y6 film leads to the plasma-like state, giving rise to a terahertz response characteristic for a dispersive charge transport. This transient state decays quickly into exciton gas due to fast Auger annihilation. Under low-intensity excitation, only isolated excitons are created and the plasma state is absent

A High-Mobility Low-Bandgap Poly(2,7-carbazole) Derivative for Photovoltaic Applications

A High-Mobility Low-Bandgap Poly(2,7-carbazole) Derivative for Photovoltaic Application

5,6-Bis(decyloxy)-2,1,3-benzooxadiazole-Based Polymers with Different Electron Donors for Bulk-Heterojunction Solar Cells

Four donor–acceptor (D–A) alternating low bandgap photovoltaic copolymers, using 5,6-bisalkoxylbenzooxadiazole (BX) as an electron-deficient moiety and benzodithiophene or 2,7-carbazole or fluorene as an electron-rich unit, were synthesized and well characterized. The copolymers possess good solubilities, high thermal stabilities, broad absorption, as well as low bandgap ranging from 1.52 to 1.73 eV. Their electronic and photovoltaic properties can be easily tuned by incorporating different donor moieties into the polymer backbone. The HOMO levels of the copolymers were determined by the electron-donating segments, while their LUMO levels were mainly dominated by the BX unit. The preliminary photovoltaic device based on PBDT-DTBX:PC61BM gives a PCE value of 2.9%, which shows that BX probably is a promising electron-accepting building block in organic electronics

Synthesis, Hole Mobility, and Photovoltaic Properties of Cross-Linked Polythiophenes with Vinylene−Terthiophene−Vinylene as Conjugated Bridge

A class of cross-linked polythiophenes with different ratio (2%, 4%, 8%) of vinylene−terthiophene−vinylene (VTThV) conjugated bridges (PT−VTThV2, PT−VTThV4, and PT−VTThV8) were synthesized. The cross-linking influenced the absorption spectra of the polymer solutions very little, but it resulted in blue-shift of the absorption spectra of the polymer films by ca. 28−39 nm. Cyclic voltammograms display that the p-doping/dedoping and n-doping/dedoping processes of all the cross-linked polythiophenes are reversible and the electrochemical bandgaps increased a little with the increase of the content of the conjugated bridges. The hole mobility values determined from the space-charge-limited current (SCLC) model reached 4.70 × 10-3 for PT−VTThV2, 2.58 × 10-3 for PT−VTThV4, and 9.48 × 10-4 cm2/(V s) for PT−VTThV8, respectively. The hole mobility of PT−VTThV2 with 2% VTThV conjugated bridges is about three orders higher than that of the corresponding polymer P1 without the conjugated bridges. The power conversion efficiency of the polymer solar cell based on the blend of PT−VTThV2 and PCBM (1:1, w/w) reached 1.72% under the illumination of AM 1.5, 100 mW/cm2, which is two times of that of the device based on P1. The results indicate that the cross-linking with the VTThV conjugated bridges obviously improved charge transportation the photovoltaic properties of the conjugated polymers

A Thieno[3,4-<i>c</i>]pyrrole-4,6-dione-Based Copolymer for Efficient Solar Cells

A Thieno[3,4-c]pyrrole-4,6-dione-Based Copolymer for Efficient Solar Cell

Benzo[1,2‑<i>b</i>:4,5‑<i>b</i>′]difuran-Based Donor–Acceptor Copolymers for Polymer Solar Cells

Three new benzo­[1,2-b:4,5-b′]­difuran-based donor–acceptor conjugated polymers, namely poly­{4,8-bis­(2′-ethylhexyloxy)­benzo­[1,2-b;3,4-b′]­difuran-alt-5,5-(4′,7′-di-2-thienyl-5′,6′-dioctyloxy-2′,1′,3′-benzothiadiazole)}­(PBDFDODTBT), poly­{4,8-bis­(2′-ethylhexyloxy)­benzo­[1,2-b;3,4-b′]­difuran-alt-5,5-(4′,7′-di-2-thienyl-2-octyl-2′,1′,3′-benzotriazole)}­(PBDFDTBTz), poly­{4,8-bis­(2′- ethylhexyloxy)­benzo­[1,2-b;3,4-b′]­difuran-alt-5,5-(4′,7′-di-2-thienyl-5′,6′-dioctyloxy-benzo­[c]­[1,2,5]­oxadiazole)}­(PBDFDTBO), were synthesized by Stille coupling polymerization reactions. All of the polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran and chlorobenzene with excellent film forming properties. Their structures were verified by 1H NMR and elemental analysis, the molecular weights were determined by gel permeation chromatography (GPC) and the thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The polymer films exhibited broad absorption bands. The hole mobility of PBDFDODTBT:PC71BM (1:2, w/w) blend reached up to 6.7 × 10–2 cm2·V–1·s–1 by the space-charge-limited current (SCLC) method. Preliminary photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PBDFDODTBT:PC71BM­(1:2, w/w)/Ca/Al showed an open-circuit voltage of 0.69 V, a power conversion efficiency of 4.5% and a short circuit current of 9.87 mA·cm–2

Effect of Fluorine Substitution on Photovoltaic Properties of Alkoxyphenyl Substituted Benzo[1,2-b:4,5-b′]dithiophene-Based Small Molecules

Two new small molecules, C3T-BDTP and C3T-BDTP-F with alkoxyphenyl-substituted benzo­[1,2-b:4,5-b′]­dithiophene (BDT) and <i>meta</i>-fluorinated-alkoxyphenyl-substituted BDT as the central donor blocks, respectively, have been synthesized and used as donor materials in organic solar cells (OSCs). With the addition of 0.4% v/v 1,8-diiodooctane (DIO), the blend of C3T-BDTP-F/PC₇₁BM showed a higher hole mobility of 8.67 × 10^–4 cm² V^–1 s^–1 compared to that of the blend of C3T-BDTP/PC₇₁BM. Two types of interlayers, zirconium acetylacetonate (ZrAcac) and perylene diimide (PDI) derivatives (PDINO and PDIN), were used to further optimize the performance of OSCs. With a device structure of ITO/PEDOT:PSS/donor:PC₇₁BM/PDIN/Al, the OSCs based on C3T-BDTP delivered a satisfying power conversion efficiency (PCE) of 5.27% with an open circuit voltage (<i>V</i>_oc) of 0.91 V, whereas the devices based on C3T-BDTP-F showed an enhanced PCE of 5.42% with a higher <i>V</i>_oc of 0.97 V