Eric Wei-Guang Diau

Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency

Simultaneous modification of the dye and redox shuttle boosts the efficiency of a dye-sensitized solar cell. The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.

Highly Efficient Mesoscopic Dye‐Sensitized Solar Cells Based on Donor–Acceptor‐Substituted Porphyrins

To dye for: A porphyrin chromophore, which is integrated into a donor-acceptor dye as a π-conjugated bridge (see picture), exhibits an unprecedented efficiency of 11 □ % when used as a photosensitizer in a double-layer TiO2 film. A greatly enhanced photovoltaic performance is observed when the porphyrin dye is cosensitized with a metal-free dye that has a complementary spectral response.

Novel Zinc Porphyrin Sensitizers for Dye‐Sensitized Solar Cells: Synthesis and Spectral, Electrochemical, and Photovoltaic Properties

Novel meso- or beta-derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q bands are red-shifted with respect to those of porphyrin 6. This phenomenon is more pronounced for porphyrins 3 and 4, which have a pi-conjugated electron-donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO-LUMO gap. Quantum-chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrin 5, which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO(2) films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO(2) in ratios [5]/[CDCA] = 1:1 and 1:2 have efficiencies of power conversion similar to that of an N3-based DSSC, which makes this green dye a promising candidate for colorful DSSC applications.

p-type Mesoscopic nickel oxide/organometallic perovskite heterojunction solar cells.

In this article, we present a new paradigm for organometallic hybrid perovskite solar cell using NiO inorganic metal oxide nanocrystalline as p-type electrode material and realized the first mesoscopic NiO/perovskite/[6,6]-phenyl C61-butyric acid methyl ester (PC61BM) heterojunction photovoltaic device. The photo-induced transient absorption spectroscopy results verified that the architecture is an effective p-type sensitized junction, which is the first inorganic p-type, metal oxide contact material for perovskite-based solar cell. Power conversion efficiency of 9.51% was achieved under AM 1.5 G illumination, which significantly surpassed the reported conventional p-type dye-sensitized solar cells. The replacement of the organic hole transport materials by a p-type metal oxide has the advantages to provide robust device architecture for further development of all-inorganic perovskite-based thin-film solar cells and tandem photovoltaics.

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%.

Synthesis and characterization of porphyrin sensitizers with various electron-donating substituents for highly efficient dye-sensitized solar cells

A series of porphyrin dyes with an electron-donating group (EDG) attached at a meso-position (YD1–YD8) have been designed and synthesized for use as sensitizers in dye-sensitized solar cells (DSSC). The nature of the EDG exerts a significant influence on the spectral, electrochemical and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins having an amino group show broadened Soret band and red-shifted Q bands with respect to those of reference porphyrin YD0. This phenomenon is more pronounced for porphyrins YD7 and YD8 that have a π-conjugated triphenylamine at the meso-position opposite the anchoring group. Upon introduction of an EDG at the meso-position, the potential for the first oxidation alters significantly to the negative whereas that for the first reduction changes inappreciably, indicating a decreased HOMO-LUMO gap. Results of density-functional theory (DFT) calculations support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino-substituted porphyrins YD1–YD4, which exhibit superior photovoltaic performance among all porphyrins under investigation. With long-chain alkyl groups on the diarylamino substituent, YD2 shows the best cell performance with JSC = 13.4 mA cm−2, VOC = 0.71 V, and FF = 0.69, giving an overall efficiency 6.6% of power conversion under simulated one-sun AM1.5 illumination.

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.

Design and characterization of porphyrin sensitizers with a push-pull framework for highly efficient dye-sensitized solar cells

Novel porphyrin dyes YD14–YD17 with a push-pull framework were synthesized for dye-sensitized solar cells (DSSC); their spectral, electrochemical and photovoltaic properties were investigated. The absorption bands of these porphyrin dyes are broadened and red-shifted upon introduction of electron-donating groups (EDG) to the meso-positions via extension of π-conjugation. Electrochemical tests show that the first oxidation for these porphyrins occurs at a potential greater than that of the I−/I3− redox couple, and attachment of EDGs to the periphery of the porphyrin facilitates electron abstraction. The photovoltaic measurements show that YD14 and YD17 have a power conversion efficiency of ∼7%. Introduction of EDGs to various meso-positions is demonstrated to be achievable, and porphyrin dyes with appropriate EDGs are promising candidates for highly efficient DSSCs.

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.

Design and characterization of highly efficient porphyrin sensitizers for green see-through dye-sensitized solar cells.

YD12 (eta = 6.7%) is a green sensitizer remarkable for its outstanding cell performance beyond that of N719 (eta = 6.1%) with no added scattering layer; the additional scattering layer assists N719 in promoting the efficiency in the red shoulder of the spectrum, but has only a small effect on the improvement of the cell performance for porphyrins.