Yuancheng Qin

Ruthenium Sensitizers and Their Applications in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have attracted considerable attention in recent years due to the possibility of low-cost conversion of photovoltaic energy. The DSSCs-based ruthenium complexes as sensitizers show high efficiency and excellent stability, implying potential practical applications. This review focuses on recent advances in design and preparation of efficient ruthenium sensitizers and their applications in DSSCs, including thiocyanate ruthenium sensitizers and thiocyanate-free ruthenium sensitizers.

Quasi-solid-state dye-sensitized solar cell from polyaniline integrated poly(hexamethylene diisocyanate tripolymer/polyethylene glycol) gel electrolyte

A microporous hydrophobic polyaniline (PANi) integrated poly(hexamethylene diisocyanate tripolymer/polyethylene glycol) [poly(HDT/PEG)] gel electrolyte was successfully synthesized via a two-step aqueous solution polymerization process. An ionic conductivity of 12.11 mS cm−1 at room temperature was obtained for the PANi integrated poly(HDT/PEG) gel electrolyte, which was well characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Morphological observations showed that the resultant gel electrolyte exhibits microporous structure, providing space for holding I−/I3− liquid electrolyte. The integration of PANi with poly(HDT/PEG) causes a lower charge-transfer resistance and higher electrocatalytic activity for the I−/I3− redox reaction. A dye-sensitized solar cell with a photo-to-electric conversion efficiency of 6.81% was obtained by sandwiching PANi integrated poly(HDT/PEG) gel electrolyte between a TiO2 anode and a Pt counter electrode, under illumination with simulated solar light of 100 mW cm−2 (AM 1.5).

Imbibition of polypyrrole into three-dimensional poly(hydroxyethyl methacrylate/glycerol) gel electrolyte for robust quasi-solid-state dye-sensitized solar cells

Hydrophobic poly(hydroxyethyl methacrylate/glycerol) [poly(HEMA/GR)] gel with a three-dimensional (3D) framework was successfully fabricated and employed to integrate with polypyrrole (PPy). The resultant PPy imbibed poly(HEMA/GR) gel electrolyte exhibited interconnective porous structure for holding I−/I3−, giving a similar conduction mechanism and ionic conductivity to that of a liquid system but a much enhanced retention of I−/I3− redox couple. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction technique, Tafel-polarization measurements as well as electrochemical impedance spectroscopy were employed to evaluate the morphology, molecular structure, crystallinity, and the electrochemical behaviors. The results showed that the combination of PPy with poly(HEMA/GR) caused a lower charge-transfer resistance and higher electrocatalytic activity for the I−/I3− redox reaction in the gel electrolyte. The resultant quasi-solid-state dye-sensitized solar cells based on PPy imbibed poly(HEMA/GR) gel electrolyte gave an overall light-to-electric conversion efficiency of 6.63%.

Pyrazino[2,3-g]quinoxaline-based conjugated copolymers with indolocarbazole coplanar moieties designed for efficient photovoltaic applications

A series of low band gap copolymers consisting of electron-accepting pyrazino[2,3-g]quinoxaline (PQx) and an electron-donating indolo[3,2-b]carbazole and thiophene units have been designed and synthesized by Stille coupling polymerization. Their optical and electrical properties could also be facilely fine-modulated for photovoltaic application by adjusting the donor/acceptor ratios. UV-vis measurements showed that increasing the content of PQx units led to enhanced absorption. The band gaps obtained from UV-vis spectra, CV scanning, and DFT modeling all indicated a narrowing band gap with increasing the PQx content in the copolymer structure. The photovoltaic solar cells (PSCs) based on these copolymers were fabricated and tested with a structure of ITO/PEDOT:PSS/copolymer:PCBM/Ca/Al under the illumination of AM 1.5G, 100 mW cm−12. The best performance was achieved using P3/[70]PCBM blend (1 : 3) with Jsc = 9.55 mA cm−2, Voc = 0.81 V, FF = 0.42, and PCE = 3.24%, which is the highest efficiency for the PQx and indolo[3,2-b]carbazole based devices. The present results also indicate that the efficient photovoltaic materials with suitable electronic and optical properties can be achieved by just fine-tuning the ratios of the strong electron-deficient accepters and large-π planar donors.

ZnO Nanowires and Their Application for Solar Cells

Nanowires (NW) are defined here as metallic or semiconducting particles having a high aspect ratio, with cross-sectional diameters « 1 ┤m, and lengths as long as tens of microns. Well-aligned one-dimensional nanowire arrays have been widely investigated as photoelectrodes for solar energy conversion because they provide direct electrical pathways ensuring the rapid collection of carriers generated throughout the device (Tang et al., 2008), as well as affording large junction areas and low reflectance owing to light scattering and trapping (Muskens et al., 2008). Solar energy conversion is a highly attractive process for clean and renewable power for the future. Excitonic solar cells (SCs), including organic and dye-sensitized solar cells (DSSC), appear to have significant potential as a low cost alternative to conventional inorganic photovoltaic (PV) devices. The synthesis and application of nanostructures in solar cells have attracted much attention. Metal oxide nanowire (NW) arrays with large surface area and short diffusion length for minority carriers represent a new class of photoelectrode materials that hold great promise for photoelectrochemical (PEC) hydrogen generation applications. Up to now, various metal oxide nanostructures such as TiO2, ZnO, Fe2O3, ZrO2, Nb2O5, Al2O3, and CeO2 have been successfully employed as photoelectrodes in SCs. Among the above-mentioned metal oxide nanostructures, the study of TiO2 and ZnO is of particular interest due to the fact that they are the best candidates as photoelectrode used in SCs. However, the advantage offered by the increased surface area of the nanoparticle film is compromised by the effectiveness of charge collection by the electrode. For DSSCs, the traditional nanoparticle film was replaced by a dense array of oriented, crystalline nanostructures to obtain faster electron transport for improving solar cell efficiency. A typical high-efficiency DSSC (Gratzel, 2009) consists of a TiO2 nanocrystal thin film that has a large surface area covered by a monolayer of dye molecules to harvest sunlight. Comparedwith TiO2, ZnO shows higher electron mobility with similar bandgap and conduction band energies. ZnO is a direct wide bandgap semiconductor (Eg = 3.4 eV) with large exciton binding energy (~60 meV), suggesting that it is a promising candidate for stable room temperature luminescent and lasing devices. Therefore, ZnO nanowires is an alternative candidate for high efficient SCs.

BaFe12O19-chitosan Schiff-base Ag (I) complexes embedded in carbon nanotube networks for high-performance electromagnetic materials

The multiwalled carbon nanotubes/BaFe12O19-chitosan (MCNTs/BF-CS) Schiff base Ag (I) complex composites were synthesized successfully by a chemical bonding method. The morphology and structures of the composites were characterized with electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction techniques. Their conductive properties were measured using a four-probe conductivity tester at room temperature, and their magnetic properties were tested by a vibrating sample magnetometer. The results show that the BF-CS Schiff base Ag (I) complexes are embedded into MCNT networks. When the mass ratio of MCNTs and BF-CS Schiff base is 0.95:1, the conductivity, Ms (saturation magnetization), Mr (residual magnetization), and Hc (coercivity) of the BF-CS Schiff base composites reach 1.908 S cm−1, 28.20 emu g−1, 16.66 emu g−1 and 3604.79 Oe, respectively. Finally, a possible magnetic mechanism of the composites has also been proposed.

Electron transport layer-free polymer solar cells show 40% higher efficiency than using ZnO transparent cathode

The poor compatibility of inorganic materials (electron transport layer) with the active layer and an ultrathin film of conjugated polymers becomes the great obstacle to producing high-quality polymer solar cells with high-throughput roll-to-roll (R2R) method. Novel electron transport layer-free polymer solar cells have been constructed by integrating the conjugated aminoalkyl-functionalized polymer, poly[3-(5-(9,9-bis(3-(dimethylamino)propyl)-7-methyl-9H-fluoren-2-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)-6-(5-methylthiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione] (PDTFN) into the active layer. PDTFN was synthesized by different Suzuki reaction conditions to gain different molecular weights- small molecular weight (PDTFN-L) and high molecular weight (PDTFN-H). It is noteworthy that PDTFN-H can significantly enhance the power conversion efficiency of the solar cells that incorporate a photoactive layer composed of poly[(3-hexylthiophene)-2,5-diyl] (P3HT) and the fullerene acceptor [6,6-phenyl-C71-butyric acid methyl ester] (PC71BM). The power conversion efficiency varies from 2.5% for ZnO transparent cathode based solar cells to 3.6% for PDTFN-H based electron transport layer-free solar cells. This improved performance can be attributed to the following reasons: the PDTFN-H can enhance cathode electron transporting by introducing the PDTFN-H into active layer without extra coating the cathode interfacial material; besides, a favorable vertical phase separation of active layer was formed due to the PDTFN-H excellent compatibility with the bulk-heterojunction. These experimental results revealed that the electron transport layer-free polymer solar cells based on PDTFN-H can be a promising novel effective fabrication with simplified manufacturing process and lower cost.

Hyperbranched small-molecule electrolyte as cathode interfacial layers for improving the efficiency of organic photovoltaics

Small-molecule electrolytes (SMEs) have attracted increasing interests owing to their intrinsic advantages, such as high repeatability, easy purification and well-defined structures. Interfacial engineering plays crucial roles in enhancing the power conversion efficiency (PCE) of polymer solar cells (PSCs). Through a green route one-step reaction with nonhalogen solvent, we reported the design and synthesis of one novel hyperbranched SME PNSO3Na as cathode interfacial layer (CIL). Owing to containing seven moles butyl sulfonate sodium, hyperbranched SMEs PNSO3Na CIL can form interfacial dipoles, tune the interfacial energy alignment, realize environment-friendly water/alcohol processing, induce the upper active layer to form order morphology and enhance the PCE of PSCs. Based on P3HT–PC61BM active layer, the PCE of the device based on PNSO3Na CIL was dramatically enhanced from 0.8 to 3.7% compared to the bare ITO device.

Preparation and properties of La-doped barium ferrite/poly (3-methylthiophene) composites

La-doped barium ferrite/poly(3-methylthiophene)(LB/P3MTH) composites have been successfully synthesized by in suit chemical polymerization with ferrite chloride (FeCl3) as an initiator. The composites structure is investigated by X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy, and the morphology of samples is observed by transmission electron microscopy (TEM). Magnetic properties of the composites are tested by vibrating sample magnetometer. XRD analysis shows that La3+ has got into the lattice of Ba-ferrite and replaces the Ba2+ and that the best La3+ amount of La-doped Ba-ferrite is not more than 0.08. La-doped Ba-ferrite particles are coated with poly (3-methylthiophene). TEM image reveals that La-doped Ba-ferrite particles have spherical morphology and are agglomerated due to the coated polymer. P3MTH covers the ferrite surface and has crystallite boundaries, which influences the composites’ physical and chemical properties.

Tuning the performance of the non-fullerene organic solar cells by the polarizability

We report here the synthesis and characterizations of a novel series of acceptor copolymers with a broad absorption band. The acceptor polymers were synthesized as a copolymer of perylenediimide (PDI) and naphthalene imide (NDI) along with dithieno[3,2-b:2′,3′-d]silole (DTS) and N-alkyl dithieno[3,2-b:2′,3-d]pyrroles (DTP). When the dipole moment and polarizability of the acceptor polymer are compared, it is observed that when the dipole moment decreases, the polarizability becomes larger. The polarizability of polymers containing PDI is significantly greater than those containing NDI, and their polarizability change is in accordance with the change in the transient fluorescence lifetime. It was also found that the power conversion efficiency of the non-fullerene solar cell was strongly correlated to polarizability. The results demonstrate that the polarizability can be utilized to screen novel donor and acceptor polymers for the design and synthesis of high-performance solar cells.