Lie Chen

Stimuli-Responsive Multifunctional Membranes of Controllable Morphology from Poly(vinylidene fluoride)-graft-Poly[2-(N,N-dimethylamino)ethyl methacrylate] Prepared via Atom Transfer Radical Polymerization

Poly(vinylidene fluoride) (PVDF) with poly[2-(N,N-dimethylamino) ethyl methacrylate] (PDMAEMA) side chains were synthesized via vinylidene fluoride-initiated atom transfer radical polymerization (ATRP) of 2-(N,N-dimethylamino) ethyl methacrylate (DMAEMA). The graft copolymer can be readily cast into porous pH- and thermo-responsive microfiltration (MF) membranes with enriched living PDMAEMA graft chains on the surface (including the pore surfaces) by phase inversion in an aqueous medium. The morphology and surface composition of the membranes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The pH and temperature of the aqueous media for phase inversion and the PDMAEMA content in the PVDF-g-PDMAEMA copolymers can be used to adjust the pore size of the membranes. In addition to having pH and temperature-responsive permeability, the PVDF-g-PDMAEMA MF membranes also exhibit both good antifouling and antibacterial properties, making the membrane potentially useful for biorelated applications. Furthermore, the dormant PDMAEMA chain ends on the PVDF-g-PDMAEMA membrane can be reactivated for the consecutive surface-initiated ATRP of other functional monomers, such as 2-naphthyl methacrylate (2NM), to produce fluorescent PDMAEMA-b-P2NM diblock copolymer brushes on the PVDF membrane.

Influence of water-soluble polythiophene as an interfacial layer on the P3HT/PCBM bulk heterojunction organic photovoltaics

Novel HT-poly[3-(6′-N,N,N-trimethylammonium)-hexyl thiophene] (P3HTN) is developed and the use of the water-soluble thiophene as an interfacial layer for low-cost poly(3-hexylthiophene):phenyl-C61 butyric acid methyl ester (P3HT:PCBM) organic photovoltaic cells with high stability in air is investigated. When P3HTN is simply inserted between the active layer and the cathode as an interfacial dipole layer by spin-coating, the open-circuit voltage (Voc) and short-circuit current density (Jsc) of photovoltaic cells with high work function Al metal cathodes dramatically increase. Resulting from a reduction of the metal work function and improved electron extraction efficiency, the power conversion efficiency (PCE) of the devices annealed in air is enhanced from 1.8% to 3.28%. In particular, the analogue of the active layer as a buffer layer could improve interchain interactions between the P3HT and the P3HTN to modify the interfacial contact, consequently obtaining an unattainable enhancement Jsc, with respect to the interlayer polymer replaced with an unanalogous conjugated polymer. The results would supply useful information to understand the contribution of an interfacial layer on the photovoltaic performance.

Triple Dipole Effect from Self‐Assembled Small‐Molecules for High Performance Organic Photovoltaics

A novel triple dipole effect has been observed for Cl-assisted self-assembled small-molecules on ITO substrate, and a highest polymer solar cell performance of 9.2% is obtained.

Self-assembly of discotic liquid crystal decorated ZnO nanoparticles for efficient hybrid solar cells

Efficient hybrid solar cells based on a blend of poly(3-hexylthiophene) (P3HT) and discotic liquid crystal ligands dithiol-functionalized triphenylene (TP-S) modified zinc oxide (ZnO) nanoparticles (TP-S@ZnO) were systematically investigated. The TP-S-modified ZnO nanoparticles possess a well-defined dispersibility, especially after annealing under the liquid-crystalline state (130 °C), originating from the help of the supramolecular self-assembly of the TP-S discs. Discotic liquid crystal ligands improve the compatibility between P3HT polymer and ZnO nanoparticles, which is beneficial for enhanced charge separation and transfer efficiency. On the other hand, the interfacial molecules TP-S can play a great role in the ordering and crystallinity of P3HT chains. X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) studies indicate that the spontaneous self-assembly of the promotes P3HT chains to overall, the power conversion efficiency (PCE) of polymer/ZnO hybrid solar cells increased from 0.46% to 0.95% after ZnO was modified with TP-S under thermal annealing. As expected, DLC molecular interface modification can provide a viable and interesting method to promote the compatibility and a large interfacial area between polymers and nanocrystals, subsequently improving the performance of photovoltaic devices.

Interface-induced face-on orientation of the active layer by self-assembled diblock conjugated polyelectrolytes for efficient organic photovoltaic cells

Systematic investigation of the instinctive self-assembly of diblock conjugated polyelectrolytes (CPEs) as electron transport layers (ETLs) on the arrangement and morphology of the upper active layer in polymer solar cells (PSCs) is usually ignored. The two water/alcohol-soluble diblock CPEs with different terminal ionic groups, PFEO-b-PTNBr and PFEO-b-PTImBr, offer an ohmic contact between the ITO electrode and the active layer by substantially reducing the work function of ITO via modulation of the interfacial dipoles. More intriguingly, the spontaneous self-assembly of the diblock polymers causes an ordered scolopendra-like conformation to develop on the ITO cathode. These self-assembled diblock CPEs can act as a template to further partially induce a preferable face-on orientation of the donor component. Surprisingly, n-type self-doping is observed in the two CPEs based on the p-type conjugated backbone, particularly in PFEO-b-PTImBr with imidazolium salt. As a result, the power conversion efficiencies (PCEs) of the devices based on PTB7-Th:PC71BM are remarkably enhanced to 9.0% for PFEO-b-PTNBr and 9.4% for PFEO-b-PTImBr. Intriguingly, both ZnO/PFEO-b-PTNBr and ZnO/PFEO-b-PTImBr based PTB7-Th:PC71BM devices exhibit superior PCEs compared to that of the classical published and commonly used PFN (8.42%) and PFNBr (8.38%) ETLs based devices. These results indicate that the development of self-assembled diblock CPEs opens a new point of view and provides a straightforward approach to achieve high performance polymer solar cells by simultaneously modulating the morphology of the interlayer, active layer and interfacial work function.

In situ polymerization of ethylenedioxythiophene from sulfonated carbon nanotube templates: toward high efficiency ITO-free solar cells

Sulfonated carbon nanotubes (SCNTs) act as secondary polymerization templates for in situ preparation of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). It essentially reduces the content of insulating PSS, instead of pre- or post-solvent processing, for a highly conductive PEDOT:PSS:SCNT composite electrode. The PEDOT:PSS:SCNT was characterized with regard to its composition, conformation, stability, morphology, optoelectronic devices, and work function behavior. The PEDOT:PSS:SCNT films with a low work function (4.4 eV) and remarkable optoelectronic properties (over 3500 S cm−1, ∼83% transmittance at a 70 nm thickness film) were suitably integrated as a cathode in organic solar cells (OSCs) with a power conversion efficiency (PCE) of 9.91% and perovskite solar cells (PSCs) with a PCE of 13.31%.

Amphiphilic fullerenes modified 1D ZnO arrayed nanorods-2D graphene hybrids as cathode buffer layers for inverted polymer solar cells

Amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) is synthesized to modify uniform ZnO arrayed nanorods (ANs) grown in situ on the surface of poly(N-vinyl pyrrolidone) decorated reduced graphene oxide (RGO). The two dimensional (2D) graphene provides a stable and conductive flat substrate for one dimensional (1D) arrayed nanorods with reduced defects. The addition of amphiphilic C60-PEG can improve the compatibility of the cathode buffer layer and the active layer. Moreover, C60-PEG produces a modified efficacy on the arrayed nanorods with reduced defects and decreased work function. Compared to the bare ZnO ANs, the C60-PEG modified ZnO ANs@RGO cathode buffer layer can reduce the recombination of carriers, increase the electron mobility and enhance electron extraction. As a result, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7)u2006:u2006[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is improved to 8.1% with better long-term stability.

Control of the oxidation level of graphene oxide for high efficiency polymer solar cells

Graphene oxides (GOs) have been used as interfacial layers for fabricating more stable organic solar cells (OSCs). However, the influence of the degree of oxidation of GOs on their optoelectronic properties has been ignored. In this article, a series of GOs with different degrees of oxidation were successfully synthesized, by controlling the amount of oxidant KMnO4 during the oxidation process of graphite. With increasing oxidation level, more oxygenated functional groups were attached to the carbon basal plane and more defects were introduced into the GO sheets, resulting in an increased work function (WF) and a decreased conductivity. Meanwhile, the film-forming property of GOs was improved with increasing oxidation level, which is attributed to the adequate exfoliation of the GO sheets. After carefully controlling the oxidation level of GOs, the OSCs with GOs as the hole transport layer (HTL) show an efficiency value of 3.0%, comparable to that with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (3.2%), originating from the good film-forming property, appropriate work function and high conductivity.

Liquid-crystalline ionic liquids modified conductive polymers as a transparent electrode for indium-free polymer solar cells

Ordered microstructure and high conductivity of poly(3,4-ethylenedioxythiophene):poly-(styrene sulfonate) (PEDOT:PSS, commercial product PH1000) films for a transparent anode were obtained by liquid-crystalline ionic liquids modification. By spin-coating 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16MIm]PF6) or 1-hexadecyl-3-methylimidazolium tetrafluoroborate ([C16MIm]BF4) on the PH1000 film, half of the insulating PSS on the top surface of PH1000 could be successfully removed and the PEDOT formed an ordered and continuous molecular packing. The conductivity of PH1000 dramatically increased from 0.4 S cm−1 to 1457.7 S cm−1 for PH1000/[C16MIm]PF6 and 1243.8 S cm−1 for PH1000/[C16MIm]BF4. At the same time, spontaneous orientation of the liquid-crystalline ionic liquids with liquid-crystallinity further promoted the ordered packing arrangement of both PH1000 and the active layer. The power conversion efficiency based on PH1000/[C16MIm]PF6 and PH1000/[C16MIm]BF4 as the anode is comparable to that obtained from the device with indium tin oxide (ITO) as the anode. In addition, liquid-crystalline ionic liquids modification is also good for the energy alignment, facilitating charge injection and transport, without any extra hole transport layer. Furthermore, these novel liquid-crystalline ionic liquids modification PH1000 anodes have potential applications in the fabrication of ITO-free large-area flexible printed polymer solar cells.

Integration of light-harvesting complexes into the polymer bulk heterojunction P3HT/PCBM device for efficient photovoltaic cells

The major light-harvesting chlorophyll (Chl) a/b-binding protein of photosystem II (LHCIIb) in plants is the most abundant membrane protein on earth. During the evolution of photosynthesis over more than 3.4 billion years, this light harvesting system has developed the most effective membrane protein for harnessing solar energy. Because of its high efficiency in absorbing and transferring solar energy, LHCIIb is becoming more and more attractive for mankinds effort to utilize solar energy. Here, we demonstrate the integration of LHCIIb with a P3HT/PCBM bulk heterojunction, in which a P3HT/PCBM active layer, instead of the “reaction centers” in photosystem II (PSII), absorbs the energy transfer from LHCIIb, consequently enhancing the solar energy utilization effectively in solid-state photovoltaic devices. The electronic integration into devices, achieved by inserting a layer of LHCIIb and then coating with a P3HT/PCBM active layer, can remain stable for several weeks. The energy transfer from LHCIIb to P3HT plays an important role in the increase in photocurrent density and broadens the solar absorption spectrum of the control device. The fabricated photovoltaic cells with an LHCIIb interfacial layer achieved an approximately 30% enhancement in the photocurrent and internal quantum efficiencies. Although the heat inactivation effect of the device limits the optimization of the normal structure, the pre-annealing treatment of the inverted organic photovoltaic (OPV) devices is used to realize an improvement in the photoconversion performance.