Optimizing dyes for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have emerged as an important cheap photovoltaic technology. Charge separation is initiated at the dye, bound at the interface of an inorganic semiconductor and a hole-transport material. Careful design of the dye can minimize loss mechanisms and improve light harvesting. Mass application of DSSCs is currently limited by manufacturing complexity and long-term stability associated with the liquid redox electrolyte used in the most-efficient cells. In this Minireview, dye design is discussed in the context of novel alternatives to the standard liquid electrolyte. Rapid progress is being made in improving the efficiencies of such solid and quasi-solid DSSCs which promises cheap, efficient, and robust photovoltaic systems.     

Arylamine-based dyes for p-type dye-sensitized solar cells

New arylamine-based sensitizers for p-type dye-sensitized solar cells (DSSCs) have been synthesized and used for p-type DSSCs. The best conversion efficiency reaches ～0.1%. Sensitizers with two anchoring carboxylic acids lead to higher open-circuit voltages, short-circuit currents, and energy conversion efficiencies.     

Coplanar indenofluorene-based organic dyes for dye-sensitized solar cells

A series of new organic dyes, comprising indenofluorene moiety as a conjugated bridge, with an extended π-groups, such as thiophene and furan, diphenylamine as donor, cyanoacrylic acid group as an electron acceptor and anchoring group, have been synthesized. Photophysical and electrochemical measurements, and theoretical computation were carried out on these dyes. Dye-sensitized solar cells (DSSCs) using these dyes as the sensitizers exhibited photocurrent density (J_SC), open-circuit voltage (V_OC), and fill factor (FF) in the range of 6.95–8.20 mA/cm², 0.70–0.71 V, and 0.69–0.71, respectively, corresponding to an overall conversion efficiency of 3.36–4.05%. The best efficiency reached 56% of the standard cell based on N719.     

Highly-efficient metal-free organic dyes for dye-sensitized solar cells

A solar-to-electric conversion efficiency of 6.1% is achieved with this new dye, compared to 6.3% for N3 dye under the same experimental conditions. Although these indoline dyes are slightly less efficient than N3 dye, the cost of indoline dye is much less than for N3 due to ease of preparation. Furthermore, indoline dyes are shown to be highly stable to photoredox processes by cyclic voltammogram.     

New tetrazole-based organic dyes for dye-sensitized solar cells

A series of new metal-free organic dyes that contain donors with triphenylamine or its derivatives and tetrazole-based acceptors were synthesized and characterized by photophysical, electrochemical, and theoretical computational methods. They were applied in nanocrystalline TiO_2 solar cells(DSSCs). It is found that the introduction of diphenylamine units as antennas in the as-synthesized dyes could improve photovoltaic performance compared with phenothiazine and carbazole units as antennas in DSSCs. The dye with(2H-tetrazol-5-yl) acrylonitrile electron acceptor also displayed the highest solar-to-electrical energy conversion efficiency.     

Novel pyrenoimidazole-based organic dyes for dye-sensitized solar cells

A novel class of organic dyes containing pyrenoimidazole donors, cyanoacrylic acid acceptors, and oligothiophene π-linkers has been synthesized and characterized. The electro-optical properties of these dyes can be tuned by changing the conjugation length of the π-linkers. A dye containing terthiophene in the conjugation pathway exhibited a solar energy-to-electricity conversion efficiency of 5.65%.     

Novel organic dyes for efficient dye-sensitized solar cells

Two novel metal-free organic dyes containing thienothiophene and thiophene segments have been synthesized. Nano-crystalline TiO2 dye-sensitized solar cells were fabricated using these dyes as light-harvesting sensitizers, and a high solar energy-to-electricity conversion efficiency of 6.23% was achieved.     

Oligothiophene-containing coumarin dyes for efficient dye-sensitized solar cells

We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.     

Metal-free organic dyes for dye-sensitized solar cells: recent advances

1. Download : Download full-size image

     

Novel polyene dyes for highly efficient dye-sensitized solar cells

We have developed an efficient and novel polyene-dye-sensitized nanocrystalline TiO2 solar cells producing a 6.8% solar energy-to-electricity conversion efficiency (eta) under AM 1.5 irradiation (100 mW cm(-2)): short-circuit current density (Jsc), 12.9 mA cm(-2), open-circuit photovoltage (Voc), 0.71 V, fill factor (ff), 0.74.     

Organic dyes incorporating low-band-gap chromophores for dye-sensitized solar cells

Versatile dyes based on benzothiadiazole and benzoselenadiazole chromophores have been developed that perform efficiently in dye-sensitized solar cells. Power conversion efficiency of 3.77% is realized for a dye in which charge recombination is probably hindered by the nonplanar charge-separated structure.     

Starburst triarylamine based dyes for efficient dye-sensitized solar cells

We report here on the synthesis and photophysical/electrochemical properties of a series of novel starburst triarylamine-based organic dyes (S1, S2, S3, and S4) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). For the four designed dyes, the starburst triarylamine group and the cyanoacetic acid take the role of electron donor and electron acceptor, respectively. It was found that the introduction of starburst triarylamine group to form the D-D-pi-A configuration brought about superior performance over the simple D-pi-A configuration, in terms of bathochromically extended absorption spectra, enhanced molar extinction coefficients and better thermo-stability. Moreover, the HOMO and LUMO energy levels tuning can be conveniently accomplished by alternating the donor moiety, which was confirmed by electrochemical measurements and theoretical calculations. The DSSCs based on the dye S4 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 85%, a short-circuit photocurrent density (J(sc)) of 13.8 mA cm(-2), an open-circuit photovoltage (V(oc)) of 0.63 V, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.02% under 100 mW cm(-2) irradiation. This work suggests that the dyes based on starburst triphenylamine donor are promising candidates for improvement of the performance of the DSSCs.     

Recent advances in phenothiazine-based dyes for dye-sensitized solar cells

Dye-sensitized solar cells(DSSCs) have attracted significant attention as alternatives to conventional silicon-based solar cells owing to their low-cost production,facile fabrication,excellent stability and high power conversion efficiency(PCE).The dye molecule is one of the key components in DSSCs since it significant influence on the PCE,charge separation,light-harvesting,as well as the device stability.Among various dyes,easily tunable phenothiazine-based dyes hold a large proportion and achieve impressive photovoltaic performances.This class of dyes not only has superiorly non-planar butterfly structure but also possesses excellent electron donating ability and large π conjugated system.This review summarized recent developments in the phenothiazine dyes,including small molecule phenothiazine dyes,polymer phenothiazine dyes and phenothiazine dyes for co-sensitization,especially focused on the developments and design concepts of small molecule phenothiazine dyes,as well as the correlation between molecular structures and the photovoltaic performances.     

Theoretical study of new ruthenium-based dyes for dye-sensitized solar cells

Two relevant, recently reported, ruthenium-based complexes to be used as sensitizers in Gra?tzel photovoltaic cells are theoretically studied. The UV/vis absorption spectra have been computed within the time-dependent density functional theory formalism. The obtained excitation energies are compared with the experimental results, and the nature of the transition is analyzed in terms of the electronic density. A preliminary study on the performance of different functionals against the equation of motion coupled cluster is performed on a smaller model system.     

5-Phenyl-iminostilbene based organic dyes for efficient dye-sensitized solar cells

Four new 5-phenyl-iminostilbene dyes (ISB-3–6) containing electron-withdrawing benzo-[c][1,2,5]thiadiazole have been designed and synthesized for use as DSSCs. Their absorption properties and electrochemical and photovoltaic performances have been investigated systematically. Among these dyes, DSSCs based on a dye containing benzo-[c][1,2,5]thiadiazole and benzene moieties (ISB-4) showed the best performance: a short-circuit photocurrent density (J_sc) of 13.69 mA cm⁻², an open-circuit photovoltage (V_oc) of 722 mV, and a fill factor (FF) of 0.71, which corresponds to a power conversion efficiency (PCE) of 6.71%, under optimized conditions. Additionally, long-term stability of the ISB-4 based DSSCs with ionic-liquid electrolytes was demonstrated under 1000 h of light soaking, the photovoltaic performance is up to 5.75%. The results suggest that 5-phenyl-iminostilbene containing dyes are promising candidates for application in DSSCs.     

Y-shaped dyes based on triphenylamine for efficient dye-sensitized solar cells

Three new triphenylamine-based dyes with Y-shaped conformation bearing triphenylamino-vinyl, 10-octyl-10H-phenothiazine-vinyl and 9-octyl-9H-carbazole-vinyl as arms (TT, TP, and TC) have been synthesized. From electrochemical investigations it is found that they can be employed in DSSCs due to the balanced HOMO and LUMO energy levels. Notably, the photo-to-electrical conversion efficiency of the DSSCs sensitized with branched TT, TP, and TC reach 5.12%, 4.84%, and 3.63%, which are higher than that sensitized with T (2.79%), and the DSSC sensitized with TT shows higher IPCE response and better photovoltaic performances (J_sc=12.37 mA/cm², V_oc=0.72 V and ff=0.58) than others. These results reveal that the introduction of branched Y-shaped extended π-conjugated donors to D-π-A dyes cannot only enlarge the spectral response range, but also suppress the molecular aggregation on TiO₂ films to a certain extent, which would enhance the performance of DSSCs.     

Macrocyclic triphenylamine based organic dyes for efficient dye-sensitized solar cells

A novel class of organic D-π-A dyes employing macrocyclic triphenylamine dimer as electron donor was designed and synthesized for dye-sensitized solar cells. The prepared compounds showed high chemical and elelctrochemical stabilities as well as good long-wave absorption. Photovoltaic devices based on these dyes showed high open circuit voltage (higher than that of N3) and achieved a solar energy to electricity conversion efficiency of 6.31%. All the performances indicate the dyes containing macrocyclic triphenylamine dimer is a good candidate for dyes sensitized solar cells.     

Efficient and stable panchromatic squaraine dyes for dye-sensitized solar cells

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.     

Efficient iodine-free dye-sensitized solar cells employing truxene-based organic dyes

Two new truxene-based organic sensitizers (M15 and M16) featuring high extinction coefficients were synthesized for dye-sensitized solar cells employing cobalt electrolyte. The M16-sensitized device displays a 7.6% efficiency at an irradiation of AM1.5 full sunlight.