Jiefeng Hai

Naphthodifuran alternating quinoxaline copolymers with a bandgap of ∼1.2 eV and their photovoltaic characterization

Four new alternating copolymers of naphthodifuran and quinoxaline have been developed. With the bandgap as low as 1.2 eV, polymers exhibited extended absorption to 1200 nm. Their potential in bulk heterojunction solar cells was evaluated. With device optimization, triazoloquinoxaline based polymers contributed the highest power conversion efficiency of 0.84%.

Design and synthesis of triazoloquinoxaline polymers with positioning alkyl or alkoxyl chains for organic photovoltaics cells

Four benzodithiophene-triazoloquinoxaline alternating polymers, PBDTT-BTzQx-EH-C1, PBDT-BTzQx-EH-C1, PBDT-BTzQx-EH-C12 and PBDT-BTzQx-C12, have been designed and synthesized to investigate the correlation of alkyl side chains with the opto-electronic properties of the resulting polymers. The introduction of side chains onto the thiophene spacer or quinoxaline unit lowers the highest occupied molecular orbital energy level of the polymers, while excessive chains prevent the polymer backbone from π–π stacking and result in a decreased short circuit current and fill factor in a photovoltaic application. The bulk heterojunction cells fabricated by blending PBDTT-BTzQx-EH-C1 with [6,6]-phenyl-C61-butyric acid methyl ester exhibit a best power conversion efficiency (PCE) of 1.40%, with a short-circuit current density of 4.12 mA cm−2, an open-circuit voltage of 0.62 V and a fill factor of 55%. The device was further optimized to 2.24% PCE by using PFN (5 nm)/Ca (5 nm) as a co-interfacial layer.

Direct access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes with deep low-lying HOMO levels and high mobilities

A general methodology has been proposed for the straightforward access to 4,8-functionalized benzo[1,2-b:4,5-b′]dithiophenes (BDTs) via Pd mediated coupling reactions including Suzuki–Sonogashira coupling and carbon–sulfur bond formation reactions. This versatile platform can be used to construct a library of BDT core centred conjugated systems, featuring large fused-ring structure and good charge mobility, where a hole mobility of 0.061 cm2 V−1 s−1 is demonstrated. With the energy level fine-tuned with functionalization, the charge transporting BDTs show great potential for donor–acceptor polymers.

Monosubstituted dually cationic cyclodextrins for stronger chiral recognition

Novel monosubstituted dually cationic cyclodextrins (CDs) have been synthesized by anchoring different alkyl chain spaced imidazolium and ammonium sidearm onto the CD primary ring. These cationic CDs exhibit satisfactory enantioselectivities for amino acids and acidic racemates in aqueous capillary electrophoresis.

Correlation of structure and photovoltaic performance of benzo[1,2-b:4,5-b′]dithiophene copolymers alternating with different acceptors

Four π-conjugated benzo[1,2-b:4,5-b′]dithiophene (BDT) based polymers were synthesized for application in polymer solar cells. These polymers possessed desirable HOMO/LUMO levels for polymer photovoltaic applications. PBDTT–TTz and PBDTT–DTBT displayed strong absorption in the range of 300–650 nm, while PBDTT–DPP and PBDTT–TTDPP showed a further 100 nm extended absorption band. The lowest unoccupied molecular orbital energy levels of polymers were tuned effectively from −3.34 eV to −3.81 eV by fusing with different accepting units. A maximum power conversion efficiency of 2.60% was obtained from photovoltaic cells with a PBDTT–TTz : PC61BM (1 : 2, w/w) blend film as the active layer, with a short circuit current density of 8.37 mA cm−2, an open circuit voltage of 0.70 V, and a fill factor of 44.3%.

A versatile strategy to directly synthesize 4,8-functionalized benzo[1,2-b:4,5-b′]difurans for organic electronics

A direct synthesis of 4,8-functionalized benzo[1,2-b:4,5-b′]difurans (BDFs) is developed. By fine-tuning the energy levels with different 4,8-functionalities or incorporating with electron-accepting units, BDFs show great potential as organic electronic materials, as demonstrated by 4.61% power conversion efficiency for polymer solar cells.

Benzotrithiophene polymers with tuneable bandgap for photovoltaic applications

Four benzotrithiophene (BTT) based donor–acceptor polymers have been prepared by alternating with diketopyrrolopyrrole (DPP), thiazolo[5,4-d]thiazole (TTz), thieno[3,4-c]pyrrole-4,6-dione (TPD) and thiadiazolo[3,4-g]quinoxaline (DTBTQx). The BTT-based polymers possess good solubility in common organic solvents and excellent thermal stability. PBTTDPP and PBTTDTBTQx possessed an optical bandgap of 1.27 eV and 1.20 eV, with absorption spectra extending to the near-infrared region. The bulk-heterojunction solar cells delivered a highest PCE of 1.39%, with a short circuit current of 5.46 mA cm−2, an open-circuit voltage of 0.51 V and a fill factor of 0.50.

Doping a D-A structural polymer based on benzodithiophene and triazoloquinoxaline for efficiency improvement of ternary solar cells

A novel donor-acceptor (D-A) structural polymer PBDT-BTzQx-C12 consisting of benzodithiophene and triazoloquinoxaline units as donor and acceptor building blocks was synthesized. The PBDT-BTzQx-C12 was evaluated as complementary electron donor in polymer solar cells (PSCs) with poly(3-hexylthiophene) (P3HT) as electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as electron acceptor. The power conversion efficiencies (PCEs) of PSCs were improved from 3.18% to 3.54% by doping 2 wt. % PBDT-BTzQx-C12, corresponding to an approximately 11% PCE improvement. The performance improvement of ternary PSCs should be attributed to the increase of photon harvesting and the optimized phase separation of active layers by doping D-A structural PBDT-BTzQx-C12.

Cyclodextrin-Based Chiral Stationary Phases for Gas Chromatography

In this chapter, cyclodextrin-based chiral stationary phases (CSPs) developed for the enantiomeric separation using gas chromatography are reviewed. A correlation of the CD structure and the enantioselectivities of the resultant CSPs are discussed.

Anionic Cyclodextrins for Capillary Electrophoresis

The development of different types of modified cationic cyclodextrins including C(6) persubstituted, randomly multi-substituted, selectively disubstituted, and monosubstituted derivatives as well as C(2) monosubstituted derivatives for enantiomeric separation in capillary electrophoresis is summarized in this chapter. The analytical parameters for optimization of enantiomeric separation with these cyclodextrins are elaborated. The NMR study to reveal the recognition mechanism of cyclodextrin derivatives towards selectands is also discussed.