Chin-Li Wang

A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells

We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency η = 10.17%.

Enveloping porphyrins for efficient dye-sensitized solar cells

A series of porphyrins bearing alkoxyl and/or alkyl chains were prepared to investigate the roles of alkoxyl/alkyl chains in the enhanced photovoltaic performance of the dyes. Based on the experimental results and the molecular simulations, we demonstrated that suitable long alkoxyl chains are capable of wrapping the porphyrin core, thus resulting in decreased dye aggregation, elevated excited states and LUMOs, and improved photovoltaic performance.

Enhanced photovoltaic performance with co-sensitization of porphyrin and an organic dye in dye-sensitized solar cells

We designed a stepwise approach for co-sensitization of a zinc porphyrin sensitizer (LD12) with a spirally configured organic dye (CD5) for dye-sensitized solar cells. The co-sensitized LD12 + CD5 device showed significantly enhanced VOC and JSC relative to its individual single-dye sensitized devices. Upon optimization, the device made of the LD12 + CD5 system yielded JSC/mA cm−2 = 16.7, VOC/V = 0.74, FF = 0.73 and η = 9.0%; this performance is superior to that of either individual device made from LD12 (η = 7.5%) and CD5 (η = 5.7%) under the same conditions of fabrication. To understand the effects of the potential shift and charge recombination on the cell performance, we measured charge-extraction (CE) and intensity-modulated photovoltage spectra (IMVS). Upon sensitization with each dye, the TiO2 potentials are similar, but co-sensitization causes the potential to shift down (cathodic shift). Charge recombination was significantly retarded for the co-sensitized system relative to each individual dye-sensitized system, to account for the enhanced VOC for the former relative to the latter. A test of stability indicates a systematic trend between the LD12 + CD5 and LD12 devices; the performance of the co-sensitized device degraded only ∼15% and remained stable during the period of 500–1000 h near 295 K.

Porphyrins for efficient dye-sensitized solar cells covering the near-IR region

A series of new porphyrins (LWP1–4) for dye-sensitized solar cells (DSSCs) were prepared by attaching pyrene or a 4-dimethylaminophenyl group in combination with anthracene to modify the porphyrin core. Fundamental studies showed that incorporation of these moieties renders feasible tuning of spectral and redox properties of the porphyrins. Significantly, DSSCs adopting the LWP1 dye exhibit energy conversion up to 800 nm without compromising the overall efficiency. This achievement is attributed to the collective effects of the broadened and red-shifted IPCE spectra, elevated energy levels at the excited states of the dyes, suitable dye soaking processes, and suitable electron-donating substituents.

Panchromatic co-sensitization of porphyrin-sensitized solar cells to harvest near-infrared light beyond 900 nm

We designed a dimeric porphyrin dye (LDD1) based on an efficient push–pull zinc porphyrin (LD14) with extended π-conjugation through coupling of two zinc porphine cores via an acetylene bridge at the meso position of the porphyrin to extend the absorption spectrum effectively into the near infrared region. The effect of dye aggregation among porphyrin molecules was significantly suppressed when the LDD1 and LD14 dyes were co-sensitized on a nanocrystalline TiO2 film in a dye-sensitized photovoltaic system. The light-harvesting ability of the device exhibits a panchromatic feature covering a broad spectral region from 400 nm to 900 nm, which results in a short-circuit current density of 21.3 mA cm−2 and a power conversion efficiency of 10.4% in an iodine-based solar cell.

Porphyrins bearing a consolidated anthryl donor with dual functions for efficient dye-sensitized solar cells

Three porphyrin dyes with different electron-donating groups were prepared to compare their photovoltaic performance in dye-sensitized solar cells. LWP12 is based on LD31 which has a complicated, piece-together electron-donating group, whereas LWP13 and LWP14 have merged substituents with electron-donating and absorption-broadening abilities. The results in this work suggest that consolidated anthryl donors may be used to design highly efficient photosensitizers.

A novel porphyrin-containing polyimide for memory devices

We design a novel solution-processable polyimide ZnPor-t-DSDA with porphyrin moiety (electron donor) and sulfone-containing phthalimide (electron acceptor) for polymer memory applications. The resulting memory device can be switched from low-conductivity (OFF) to high-conductivity (ON) by both positive and negative sweeps, exhibiting symmetry biswitching characteristic with a short retention time (30 s). On the basis of the simulation calculation, the coplanar structure between donor and acceptor units results in charge transferring easily back to its original state after being excited by an electric field.

Electrochemistry and spectroelectrochemistry of carboxyphenylethynyl porphyrins

Zinc 5-(4-carboxy-phenylethynyl)-10,20-biphenylporphines bearing various substituents on the 10,20-phenyl rings are studied for their electrochemical and spectroelectrochemical properties. Cyclic voltammetry and optically transparent thin-layer electrochemical measurements suggest that the first reductions of these porphyrins should be the reduction reaction of the carboxylic protons. For the porphyrin ring reactions, our study shows that the redox properties can be significantly affected by the alkoxyl chains on the 10,20-phenyl rings.

Zinc and linkage effects of novel porphyrin-containing polyimides on resistor memory behaviors

A new class of porphyrin-containing polyimides, ZnPor-s-DSDA, ZnPor-t-DSDA, Por-s-DSDA and Por-t-DSDA, were synthesized from porphyrin-containing diamines and 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride for resistor-type memory applications. The effect of the linkage and zinc metal was investigated by electrochemistry, molecular simulations, and memory behaviors. The memory devices with different retention times derived from polymers ZnPor-s-DSDA (WORM, >3 h) and ZnPor-t-DSDA (DRAM, 30 s) demonstrated the importance of the linkage effect, and the insulation property of polyimides Por-s-DSDA and Por-t-DSDA also implies a crucial memory behavior by metal chelation.

A large, ultra-black, efficient and cost-effective dye-sensitized solar module approaching 12% overall efficiency under 1000 lux indoor light

Three novel anthracene-based organic dyes, denoted as AN-11, AN-12 and AN-14, were synthesized for outdoor and indoor dye-sensitized solar cell studies. Laboratory-fabricated small cells, as well as rigid and flexible modules, were prepared and analyzed for their photovoltaic performance under simulated outdoor and indoor conditions. Owing to the panchromatic absorption of visible light, the AN-11 module gives rise to a very black color and superior photovoltaic performance. Significantly, the AN-11 rigid module with a large active area of 26.80 cm2 outperforms its Z907 counterpart under indoor conditions, reaching an overall efficiency of 11.94% under 1000 lux of T5 fluorescent light. In addition, the AN-11 module exhibits good stability during weather stress tests. Finally, the AN-11 dye is cost-effective and our studies show that the photovoltaic performance of the solar cells is not affected upon lowering the synthetic cost and increasing the synthetic scale.