Covalently Bound Clusters of Alpha-Substituted PDIRival Electron Acceptors to Fullerene for Organic Solar Cells

A cluster type of electron acceptor, TPB, bearing four α-perylenediimides (PDIs), was developed, in which the four PDIs form a cross-like molecular conformation while still partially conjugated with the BDT-Th core. The blend TPB:PTB7-Th films show favorable morphology and efficient charge dissociation. The inverted solar cells exhibited the highest PCE of 8.47% with the extraordinarily high <i>J</i>_sc values (>18 mA/cm²), comparable with those of the corresponding PC₇₁BM/PTB7-Th-based solar cells

Electron Acceptors Based on α‑Substituted Perylene Diimide (PDI) for Organic Solar Cells

Perylene diimide (PDI) derivatives functionalized at the ortho-position (αPPID, αPBDT) were synthesized and used as electron acceptors in non-fullerene organic photovoltaic cells. Because of the good planarity and strong π-stacking of ortho-functionalized PDI, the αPPID and αPBDT exhibit a strong tendency to form aggregates, which endow the materials with high electron mobility. The inverted OPVs employing αPDI-based compounds as the acceptors and PBT7-Th as the donor give the highest power conversion efficiency (PCE) values: 4.92% for αPBDT-based devices and 3.61% for αPPID-based devices, which are, respectively, 39% and 4% higher than that of their β-substituted counterparts βPBDT and βPPID. Charge separation studies show more efficient exciton dissociation at interfaces between αPDI-based compounds and PTB7-Th. The results suggest that α-substituted PDI derivatives are more promising electron acceptors for organic photovoltaic (OPV) components than β-isomers

High Performance Ternary Organic Solar Cells due to Favored Interfacial Connection by a Non-Fullerene Electron Acceptor with Cross-Like Molecular Geometry

The non-fullerene electron acceptor, TPB, exhibits a unique cross-like molecular geometry which helps it to stay preferentially at the interfaces between PTB7-Th and PC₇₁BM, when it is used as the third component in ternary OPV cells. The four PDI units connected to TPB’s core provide multiple contact points between PTB7-Th and PC₇₁BM phases, thus facilitating interfacial charge extraction and improving the overall PCE to 10.6% from 9.8% after 10% TPB was added as the third component. This paper describes detailed experimental results and a model to explain these observations

Enhancement in Open-Circuit Voltage in Organic Solar Cells by Using Ladder-Type Nonfullerene Acceptors

The open-circuit voltage (<i>V</i>_oc) loss has always been a major factor in lowering power conversion efficiencies (PCEs) in bulk heterojunction organic photovoltaic cells (OPVs). A method to improve the <i>V</i>_oc is indispensable to achieve high PCEs. In this paper, we investigated a series of perylene diimide-based ladder-type molecules as electron acceptors in nonfullerene OPVs. The D–A ladder-type structures described here lock our π-systems into a planar structure and eliminate bond twisting associated with linear conjugated systems. This enlarges the interface energy gap (Δ<i>E</i>_DA), extends electronic delocalization, and hence improves the <i>V</i>_oc. More importantly, these devices showed an increase in <i>V</i>_oc without compromising either the <i>J</i>_sc or the FF. <b>C5r</b> exhibited a strong intermolecular interaction and a PCE value of 6.1%. Moreover, grazing-incident wide-angle X-ray scattering analysis and atomic force microscopy images suggested that our fused-ring acceptors showed a suitable domain size and uniform blend films, which were not affected by their rigid molecular structures

Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution

Poly 3-aminopropyltriethoxysilane is a highly reactive high-molecular polymer because of the existence of abundant amino groups, which presents a strong affinity toward different metal cations. In view of this, the novel poly amino siloxane oligomer modified graphene oxide composite (PAS–GO) was fabricated by a facile cross-linking reaction and applied to capture U­(VI)/Eu­(III) ions from aqueous solution. The interaction mechanisms between the PAS–GO and U­(VI)/Eu­(III) were elaborated. The modification by NH₂ increased the sorption sites and improved the sorption capacities because of the synergistic effect of chelation with U­(VI)/Eu­(III). X-ray photoelectron spectroscopy revealed that nitrogen groups are involved in the removal of U­(VI)/Eu­(III) since nitrogen atoms of amine groups provided the lone pair of electrons with U­(VI)/Eu­(III) species. The maximum sorption capacity of U­(VI) and Eu­(III) on the PAS–GO at 298 K calculated by the Langmuir isotherm model was 310.63 and 243.90 mg/g, respectively. The PAS–GO could be repeatedly used for more than five cycles with slight degradation of sorption. High sorption efficiency and excellent reusability make the PAS–GO composite an ideal candidate for the capture of U­(VI)/Eu­(III) from aqueous solution

Controlled Self-Assembly of Cyclophane Amphiphiles: From 1D Nanofibers to Ultrathin 2D Topological Structures

A novel series of amphiphilic <b>TC-PEG</b> molecules were designed and synthesized based on the orthogonal cyclophane unit. These molecules were able to self-assemble from 1D nanofibers and nanobelts to 2D ultrathin nanosheets (3 nm thick) in a controlled way by tuning the length of PEG side-chains. The special structure of the cyclophane moiety allowed control in construction of nanostructures through programmed noncovalent interactions (hydrophobic–hydrophilic interaction and π–π interaction). The self-assembled nanostructures were characterized by combining real space imaging (TEM, SEM, and AFM) and reciprocal space scattering (GIWAXS) techniques. This unique supramolecular system may provide a new strategy for the design of materials with tunable nanomorphology and functionality

Development and Structure/Property Relationship of New Electron Accepting Polymers Based on Thieno[2′,3′:4,5]pyrido[2,3‑<i>g</i>]thieno[3,2‑<i>c</i>]quinoline-4,10-dione for All-Polymer Solar Cells

Several electron accepting polymers having weak accepting–strong accepting (WA-SA) and strong accepting–strong accepting (SA-SA) monomer alternation were synthesized for studies of structure/property relationship in all-polymer solar cells. Two kinds of cyclic amide monomers, 4,10-bis­(2-butyloctyl)-thieno­[2′,3′:5,6]­pyrido­[3,4-g]­thieno-[3,2-<i>c</i>]­isoquinoline-5,11-dione (TPTI) and 5,11-bis­(2-butyloctyl)-thieno­[2′,3′:4,5]­pyrido­[2,3-g]­thieno­[3,2-<i>c</i>]­quinoline-4,10-dione (TPTQ), were synthesized as weak accepting monomers (WA). Difluorinated TPTQ (FTPTQ) and well-known perylene diimide (PDI) monomers were synthesized as strong electron accepting monomers (SA). By using 1-chloronaphthalene (CN) as a cosolvent, the morphology of the polymer blended films can be finely tuned to achieve better ordering toward face-on mode and favorable phase separation between electron donor and acceptor, resulting in significant enhancement of short circuit current (<i>J</i>_<i>sc</i>) and fill factor (FF). The fluorination in the TPTQ unit reduced the dipole moment of the D–A complex and gave a negative effect on a polymer system. PFP showed worse electron accepting property with lower electron mobility than PQP. It is reasoned that the internal polarization plays an important role in the design of electron accepting polymers. As a result, <b>PQP</b> having TPTQ monomer exhibited the best photovoltaic performance with power conversion efficiency (PCE) of 3.52% (<i>V</i>_<i>oc</i> = 0.71 V, <i>J</i>_<i>sc</i> = 8.57 mA/cm², FF = 0.58) at a weight ratio of PTB7-Th:<b>PQP</b> = 1:1, under AM 1.5G

Propeller-Shaped Acceptors for High-Performance Non-Fullerene Solar Cells: Importance of the Rigidity of Molecular Geometry

This paper describes the synthesis and application of βTPB6 and βTPB6-C as electron acceptors for organic solar cells. Compound βTPB6 contains four covalently bonded PDIs with a BDT-Th core at the β-position. The free rotation of PDIs renders βTPB6 with varying molecular geometries. The cyclization of βTPB6 yields βTPB6-C with high rigidity of the molecular geometry and enlarged conjugated skeleton. The inverted solar cells based on βTPB6-C and PTB7-Th as the donor polymer exhibited the highest efficiency of 7.69% with <i>V</i>_oc of 0.92 V, <i>J</i>_<i>sc</i> of 14.9 mAcm^–2, and FF of 0.56, which is 31% higher than that for βTPB6 based devices. The larger fraction of βTPB6-C and PTB7-Th than that of βTPB6:PTB7-Th in a blend film takes a face-on orientation packing pattern for π-systems that benefits the charge transport and hence higher PCE value than that for βTPB6:PTB7-Th. It was also found that a proper DIO:DPE additive further enhances this trend, which results in an increase of the PCE value for βTPB6-C:PTB7-Th while decreasing the PCE value for βTPB6:PTB7-Th

Synthesis and Search for Design Principles of New Electron Accepting Polymers for All-Polymer Solar Cells

New electron withdrawing monomers, thieno­[2′,3′:5′,6′]­pyrido­[3,4-<i>g</i>]­thieno­[3,2-<i>c</i>]­isoquinoline-5,11­(4<i>H</i>,10<i>H</i>)-dione (TPTI) and fluorenedicyclopentathiophene dimalononitrile (CN), have been developed and used to form 12 alternating polymers having different monomer combinations: (a) weak donating monomer–strong accepting monomer, (b) weak accepting monomer–strong accepting monomer, (c) weak accepting monomer–weak accepting monomer, and (d) strong donating monomer–strong accepting monomer. It was found that lowest unoccupied molecular orbital (LUMO) energy levels of polymers are significantly determined by stronger electron accepting monomers and highest occupied molecular orbital (HOMO) energy levels by the weak electron accepting monomers. In addition, fluorescent quantum yields of the TPTI-based polymers in chloroform solution are significantly decreased as the LUMO energy levels of the TPTI series of polymers become deeper. The quantum yield was found to be closely related with the photovoltaic properties, which reflects the effect of internal polarization on the photovoltaic properties. Only the electron accepting polymers showing SCLC mobility higher than 10^–4 cm²/(V s) exhibited photovoltaic performance in blend films with a donor polymer, and the PTB7:PNPDI (1:1.8 w/w) device exhibited the highest power conversion efficiency of 1.03% (<i>V</i>_oc = 0.69 V, <i>J</i>_sc = −4.13 mA/cm², FF = 0.36) under AM 1.5G condition, 100 W/cm². We provide a large set of systematic structure–property relationships, which gives new perspectives for the design of electron accepting materials

Application of biochar derived from rice straw for the removal of Th(IV) from aqueous solution

<p>Biochar is increasingly used as a low-cost and effective adsorbent for heavy metals in wastewater. Herein, biochar pyrolyzed from rice straw was employed as an adsorbent for the removal of Th(IV) from aqueous solutions. The sorption of Th(IV) on biochar was strongly dependent on pH, but independent on ionic strength at pH < 6.4. The inner-sphere complexation dominated the sorption mechanism of Th(IV) on biochar. The competition for Th(IV) between aqueous or surface-adsorbed cations/anions and functional groups of biochar was pivotal for Th(IV) sorption. The thermodynamic data suggested that Th(IV) sorption was a spontaneous and endothermic process.</p