Zhengkun Du

Design and synthesis of novel carbazole–spacer–carbazole type conjugated microporous networks for gas storage and separation

Two novel conjugated microporous networks, P-1 and P-2, with carbazole–spacer–carbazole topological model structures, were designed and prepared by FeCl3 oxidative coupling polymerization. Monomer m-1 (fluorenone spacer) was modified with a thiophene Grignard to form the fluorenyl tertiary alcohol monomer m-2, and this step can increase the polymerization branches from four to five and incorporate the polar –OH group into the building block. N2 adsorption isotherms show that, after modification, the Brunauer–Emmett–Teller (BET) surface area of P-2 (1222 m2 g−1) is two times that of P-1 (611 m2 g−1), and the total pore volume increases 1.63 times from 0.95 to 1.55 at P/P0 = 0.99. However, the domain pore size (centred at 1.19 nm) and the pore distribution of both networks are not changed. It demonstrates that the domain pore width may be determined by the size of the rigid carbazole–spacer–carbazole backbone, not the degree of crosslinking when the networks were prepared under same polymerization conditions in this system. Hydrogen physisorption isotherms of P-1 and P-2 show that the H2 storage can be up to 1.05 wt% and 1.66 wt% at 77 K and 1.1 bar, and the isosteric heat is 9.89 kJ mol−1 and 10.86 kJ mol−1, respectively. At 273 K and 1.1 bar, the CO2 uptake capacity of P-2 can be up to 14.5 wt% which is 1.63 times that of P-1 under the same conditions. The H2 and CO2 uptake capacities of P-2 are among the highest reported for conjugated microporous networks under similar conditions. The CO2/CH4 and CO2/N2 selectivity results indicate that P-1 exhibits a slightly higher separation ability than P-2. There is often a trade-off between absolute uptake and selectivity in other microporous organic polymers. Fine design and tailoring the topological structure of the monomer can change the adsorption isosteric enthalpy and optimize the gas uptake performance. The obtained networks with the carbazole–spacer–carbazole rigid backbone show promise for potential use in clean energy applications and the environmental field.

Hyperconjugated side chained benzodithiophene and 4,7-di-2-thienyl-2,1,3- benzothiadiazole based polymer for solar cells

A novel donor–acceptor (D–A) copolymer (P3TBDTDTBT), including hyperconjugated side chained benzodithiophene as a donor and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DTBT) as an acceptor, was designed and synthesized. Due to the introduction of the hyperconjugated side chain, the resultant polymer exhibited good thermal stability with a high decomposition temperature of 437 °C, a low band-gap of 1.67 eV with an absorption onset of 742 nm in the solid film, and a deep highest occupied molecular orbital (HOMO) energy level of −5.26 eV. Finally, the polymer solar cell (PSC) device based on this polymer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) showed the best power conversion efficiency (PCE) of 3.57% with an open-circuit voltage (Voc) of 0.78 V, a short-circuit current density (Jsc) of 8.83 mA cm−2 and a fill factor (FF) of 53%.

High efficiency solution-processed two-dimensional small molecule organic solar cells obtained via low-temperature thermal annealing

A new two-dimensional (2D) organic small molecule, DCA3T(T-BDT), was designed and synthesized for solution-processed organic solar cells (OSCs). DCA3T(T-BDT) exhibited a deep HOMO energy level (−5.37 eV) and good thermal stability. The morphologies of the DCA3T(T-BDT):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends were investigated by atomic force microscopy and the crystallinity was explored by X-ray diffraction (XRD) and 2D grazing incidence wide-angle X-ray scattering (GIWAXS), respectively. The morphologies of the blends were strongly influenced by the blend ratio of DCA3T(T-BDT):PC61BM and annealing temperature. The effect of thermal annealing on the photovoltaic performance of DCA3T(T-BDT)-based small molecule organic solar cells (SMOSCs) was studied in detail. When DCA3T(T-BDT) was used as a donor with PC61BM as an acceptor, high efficiency SMOSCs with a power conversion efficiency of 7.93%, a high Voc of 0.95 V, Jsc of 11.86 mA cm−2 and FF of 0.70 were obtained by a thermal annealing process at only 60 °C, which offers obvious advantages for large scale production compared with solvent additive or interfacial modification treatment.

Novel donor–acceptor polymers containing o-fluoro-p-alkoxyphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene units for polymer solar cells with power conversion efficiency exceeding 9%

In this work, a new electron-rich building block, o-fluoro-p-alkoxyphenyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) unit, has been used to construct donor (D)–acceptor (A) conjugated copolymers with electron-deficient units 5,6-difluoro-4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (C8DTBTff) and 5,6-difluoro-4,7-di(4-hexyl-2-thienyl)-2,1,3-benzothiadiazole (C6DTBTff), named P-o-FBDTP-C8DTBTff (P2) and P-o-FBDTP-C6DTBTff (P3), respectively. The experimental results indicate that the incorporation of fluorine into the ortho-position of the alkoxyphenyl substituted BDT unit can enable its resultant polymer to efficiently tune the energy levels and improve the mobility of the derived bulk heterojunction layer, which results in a much higher power conversion efficiency (PCE) of P2 (8.10%). Moreover, replacing the 2-ethylhexyl chains on the DTBTff unit with hexyl chains can improve the planarity of the conjugated backbone of the polymer, which makes the P3/PC71BM blends exhibit higher carrier mobility than P2/PC71BM. Finally, a PCE of 9.02% for the device of P3 is obtained without any additive treatment, which is the highest value achieved for the widely reported D–A polymers with fluorine substituted BDT as the electron-donor unit in single junction polymer solar cells.

Solution-processed, indacenodithiophene-based, small-molecule organic field-effect transistors and solar cells

Two indacenodithiophene-based molecules with different side chains, BTIDT-C6 and BTIDT-OC12, have been designed and synthesized for solution-processed, small-molecule organic solar cells (OSCs) donor materials. By optimizing the side chains, the hole mobility of the materials is modulated, which has been proven by the organic field-effect transistor (OFET) performances. Solar cells based on BTIDT-C6 show a power conversion efficiency (PCE) of 4.83%. To the best of our knowledge, this is the first report about indacenodithiophene-based, solution-processed, small-molecule OFETs, and it is also one of the highest PCE reports for the indacenodithiophene-based, solution-processed, small-molecule OSCs. This report makes indacenodithiophene-based small molecules the third type of high-efficiency (5% PCE), solution-processed, small-molecule OSCs donor materials, in addition to benzodithiophene (BDT) and dithienosilole (DTS).

Efficient polymer solar cells based on a new benzo[1,2-b:4,5-b ']dithiophene derivative with fluorinated alkoxyphenyl side chain

A novel fluorine-containing benzo[1,2-b:4,5-b′]dithiophene (BDT) derivative (BDTPF) was designed to construct a donor–acceptor (D–A)-structured polymer (PBDTPF-DTBT) with the electron-withdrawing unit 4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (DTBT). The resulting polymer exhibits a broad absorption spectrum, relatively low lying HOMO energy level (−5.39 eV) and a good film-forming ability. The field-effect mobility of PBDTPF-DTBT is 0.034 cm2 V−1 s−1. Bulk heterojunction organic solar cells (OSCs) based on PBDTPF-DTBT and PC71BM were prepared and showed a good photovoltaic performance with power conversion efficiency (PCE) of 7.02%. This work demonstrates that a BDT unit with fluorinated alkoxyphenyl side chains is a promising candidate as an electron-rich building block for high performance solution-processed OSCs.

Phosphine oxide-based conjugated microporous polymers with excellent CO2 capture properties

Three novel phosphine oxide-based conjugated microporous polymers TEPO-1, TEPO-2 and TEPO-3 are designed and synthesized, which are constructed using the phosphine-based building unit tris(4-ethynylphenyl)phosphine oxide with linkers tris(4-ethynylphenyl)phosphine oxide, triphenylphosphine oxide and tri(thiophen-2-yl)phosphine oxide via Sonogashira–Hagihara homo-coupling or cross-coupling condensation reaction. The adsorption isotherms of N2 reveal that the Brunauer–Emmett–Teller (BET) specific surface areas of TEPO-1, TEPO-2 and TEPO-3 are 485 m2 g−1, 534 m2 g−1 and 592 m2 g−1, respectively. However, these three polymers have strong affinity for CO2, which exhibit relatively high sorption abilities for CO2 (273 K/1.0 bar: 6.52 wt%, 7.62 wt%, and 8.40 wt%). Meanwhile, the TEPOs demonstrate ultrahigh hydrogen uptake and outstanding CO2/CH4 selectivity compared to analogous materials with similar BET surface areas using C, Si and N as the nodes. This work reveals clearly that the gas uptake capacity of material is highly dependent on the length of the rigid skeleton and the modification of functional groups in the monomer structure.

High-Performance Small Molecule/Polymer Ternary Organic Solar Cells Based on a Layer-By-Layer Process.

UNLABELLED The layer-by-layer process method, which had been used to fabricate a bilayer or bulk heterojunction organic solar cell, was developed to fabricate highly efficient ternary blend solar cells in which small molecules and polymers act as two donors. The active layer could be formed by incorporating the small molecules into the polymer based active layer via a layer-by-layer method: the small molecules were first coated on the surface of poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) ( PEDOT PSS), and then the mixed solution of polymer and fullerene derivative was spin-coated on top of a small molecule layer. In this method, the small molecules in crystalline state were effectively mixed in the active layer. Without further optimization of the morphology of the ternary blend, a high power conversion efficiency (PCE) of 8.76% was obtained with large short-circuit current density (Jsc) (17.24 mA cm(-2)) and fill factor (FF) (0.696). The high PCE resulted from not only enhanced light harvesting but also more balanced charge transport by incorporating small molecules.

Improve the photovoltaic performance of new quinoxaline-based conjugated polymers from the view of conjugated length and steric hindrance

In this work, we have synthesized two new quinoxaline derivatives: 2,3-bis(n-octylthiomethyl)-5,8-dibromoquinoxaline (QS) and 2,3-bis[(5-octylthio)thiophen-2-yl]-5,8-dibromoquinoxaline (QTS); in addition, three new donor–acceptor (D–A) copolymers: poly{4,8-bis(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]-dithiophene-alt-2,3-bis(n-octylthiomethyl)quinoxaline} (PBDTQS), poly{4,8-bis(2-ethylhexyloxy)-benzo[1,2-b:4,5-b′]-dithiophene-alt-2,3-bis[(5-octylthio)thiophen-2-yl]quinoxaline} (PBDTQTS), and poly{2,3-bis[(5-octylthio)thiophen-2-yl]quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl} (PTQTS) were designed from the view of extending the length of conjugated side chain and reducing the steric hindrance of building blocks. Replacing the carbon atom in the side chain of polymer PBDTQS with a thiophene ring could increase the conjugation length and improve the absorption in the visible region of the copolymer PBDTQTS and PTQTS. Furthermore, polymer PTQTS exhibited a more planar backbone and increased intermolecular π-stacking compared to PBDTQTS, which was because the thiophene unit in PTQTS had smaller size and less steric hindrance than those of benzo[1,2-b:4,5-b′]-dithiophene unit in PBDTQTS. For the optimized polymer solar cell of PTQTS : PC61BM, PCE of 3.73% with Voc of 0.76 V, Jsc of 9.41 mA cm−2 and FF of 52.33% under an AM 1.5 G solar simulator with an intensity of 100 mW cm−2 was achieved, which was the best performance among the three copolymers. The results implied that the PTQTS with thiophene as the donor unit and QTS as the acceptor unit in the main chain would be a promising donor candidate in the application of polymer solar cells.

New small molecules with thiazolothiazole and benzothiadiazole acceptors for solution-processed organic solar cells

A new thiazolothiazole based small molecule (DTTz-DTBTT) has been designed and synthesized. The small molecule exhibited good thermal stability and excellent solubility. The optical gap of DTTz-DTBTT was estimated to be 1.65 eV. The solution-processed photovoltaic device based on DTTz-DTBTT and PC61BM exhibited a power conversion efficiency of 1.64%.