Structural engineering of dipolar organic dyes with an electron-deficient diphenylquinoxaline moiety for efficient dye-sensitized solar cells

A series of new organic dyes containing an electron-deficient diphenylquinoxaline moiety was synthesized and employed as the photosensitizers in dye-sensitized solar cells (DSSCs). The multiple phenyl rings in the peripheral positions of the dye structure provide a hydrophobic barrier to slow down the charge recombination. The photophysical and electrochemical properties of these dyes were investigated in detail. The cell performance and the associated photophysical and electrochemical properties can be easily tuned by the modification of the aromatic fragments within the π spacer. Dye CR204-based DSSC reached the best energy conversion efficiency of 6.49% with an open-circuit voltage of 666 mV, a short-circuit photocurrent density of 14.9 mA cm⁻², and a fill factor of 0.66. The IPCE of CR204-based DSSC covers the light-harvesting to NIR region.     

Synthesis of new truxene based organic sensitizers for iodine-free dye-sensitized solar cells

Developing arylamine photosensitizers with high extinction coefficients, proper electronic structures, and steric properties is warranted for the dye-sensitized solar cells (DSCs) employing iodine-free redox shuttles. Two new organic sensitizers (M21 and M22) featuring unsymmetrical truxene-based triarylamine donor have been synthesized and compared to its reference sensitizer M4. The effects of unsymmetrical truxene-based triarylamine donors were investigated by their absorption spectra, electrochemical and photovoltaic properties. The incorporation of strong electron donor unit (i.e., dipropylfluorene and 4-methoxybiphenyl) has resulted in an improved light harvesting capacity, and thus photocurrent as well as efficiency of cells. M22 sensitized DSCs employing the Co(II/III)tris(1,10-phenanthroline)-based redox electrolyte affords a short circuit photocurrent of 13.1 mA cm⁻², an open circuit voltage of 861 mV, and a fill factor of 0.70, corresponding to an overall conversion efficiency of 7.89% under standard AM 1.5 sunlight.     

Metal-free organic dyes with benzothiadiazole as an internal acceptor for dye-sensitized solar cells

We synthesized three metal-free organic dyes (H11–H13) consisting of a 3,6-disubstituted carbazole, benzothiadiazole, and cyanoacrylic acid. All the dyes exhibited high molar extinction coefficients and suitable energy levels for electron transfer from the electrolyte to the TiO₂ nanoparticles. Under standard AM 1.5G solar irradiation, the device using dye H13 with co-adsorbed chenodeoxycholic acid (CDCA) displayed the best performance: an open-circuit voltage (V_oc) of 0.71 V, a short-circuit current density (J_sc) of 12.69 mA cm⁻², a fill factor (FF) of 0.71, and a power conversion efficiency (PCE) of 6.32%. The PCE was ∼79% of that for commercially available N719 cells (8.02%) under the same conditions.     

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.     

Molecular design of novel indacenodithiophene-based organic dyes for efficient dye-sensitized solar cells applications

Indacenodithiophene (IDT)-based high-efficiency photovoltaics have received increasing attention recently. This paper reports a density functional theory investigation of the electronic and optical properties of three IDT-based organic dyes together with the dye/(TiO₂)₄₆ interface. In order to enhance the photoelectric properties of IDT dyes, this paper considers two methods for the structure modification of the experimentally reported dye DPInDT (J. Org. Chem. 2011, 76, 8977): the extension of the conjugation length by dithienothiophene as well as the heteroatom substitution of the bridging atoms by electron-rich nitrogen atoms. Our calculations show that both methods obviously affect the distributions of the molecular orbitals and notably red shift the absorption peaks of around 20 nm, with the former method demonstrating enhanced light harvesting efficiency. The structure modifications proposed also enhance the emission spectrum properties for IDT-based organic dyes. The calculated ultrafast injection time of electrons from the excited state of IDT dyes to the (TiO₂)₄₆ belongs to the femtosecond order of magnitude, and is ideal for efficient photoelectric conversion process in dye-sensitized solar cells (DSSCs) applications. The IDT dyes designed in this paper have good electronic and spectroscopic properties. This study is expected to provide useful guidance for the development of novel IDT dyes for applications in DSSCs.     

Redox couple related influences of bulky electron donor as well as spacer in organic dye-sensitized mesoscopic solar cells

For dye-sensitized solar cells (DSCs), it is of great significance to understand the structure–performance relationship of photosensitizers. Herein, we scrutinize the influences of the arylamine electron donors as well as the fused thiophene spacer on the optoelectronic features of thin-film DSCs employing the tris(1,10-phenanthroline)cobalt(II/III) or the iodide/triiodide redox couple. Interestingly, the incorporation of bulky dihexyloxybenzene-substituted triphenylamine (DHOB-TPA) electron donor does not resulted in an improved electron lifetime, which is sharp contrast with the conventional concept on bulky electron donor. On the other hand, the introduction of the DHOB-TPA electron donor or the dithienopyrrole spacer significantly increases the molar absorption coefficients of dyes, which govern the performance of thin-film DSCs. This work demonstrates how organic dyes must be tailored carefully depending on the electrolyte red/ox couple used.     

Highly efficient substituted triple rhodanine indoline dyes in zinc oxide dye-sensitized solar cell

Substituited triple rhodanine indoline dyes showed higher performance than known triple rhodanine derivative (D150). A few triple rhodanine indoline derivatives showed comparable conversion efficiency to D149.     

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.     

Molecular engineering of organic sensitizers containing indole moiety for dye-sensitized solar cells

Three organic dyes, JK-77, JK-78, and JK-79 containing indole unit are designed and synthesized. Nanocrystalline TiO₂ dye-sensitized solar cells were fabricated using these dyes. Under standard global AM 1.5 solar condition, the JK-79 sensitized solar cell gave a short circuit photocurrent density of 13.62 mA cm⁻², open-circuit voltage of 0.705 V, and a fill factor of 0.74, corresponding to an overall conversion efficiency η of 7.18%. We found that the η of JK-79 was higher than those of other two cells due to the higher V_oc. The improved V_oc value is attributed to the suppression of dark current owing to the blocking effect of a long alkyl chain.     

Synthesis of organosilicon polymers containing donor-acceptor type π-conjugated units and their applications to dye-sensitized solar cells

Novel organosilicon polymers having donor-acceptor type π-conjugated units in the backbone were prepared by Stille-coupling reactions of bis(tributylstannylthienyl)silanes with diiodoquinoxialine, benzothiadiazole, and benzothiaselenazole. Dehaloganative copolymerization of di(bromothienyl)silanes and dibromoquinoxaline was also studied, which gave the corresponding random copolymer. Applications of these polymers to dye-sensitized solar cells (DSSCs) were examined and it was found that the polymer containing benzoselenadiazole units as the acceptor exhibited the best performance as the sensitizer among the present polymers.     

Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced performance in dye-sensitized solar cells

We have synthesized a series of new dipolar organic dyes Bn (n=0, 1, 2) employing triarylamine as the electron-donor, 2-cyanoacrylic acid as the electron-acceptor, and fluorenevinylene as the conjugated bridge, which were used as sensitizers in dye-sensitized solar cells. It is found that the solar-energy-to-electricity conversion efficiencies of the prepared DSSCs are in the range of 2.79-5.56%, which reach 35-70% of a standard device based on N719 fabricated and measured under the same conditions. The DSSC sensitized with B1 with balanced length of conjugated bridge shows the highest photo-to-electrical energy conversion efficiency and the open-circuit photovoltage (V_oc) of 0.86 V.     

Fluorine substituent effect on organic dyes for sensitized solar cells

Two sets of organic dyes containing a stilbene backbone with fluorine substituents were designed for a study on the quantum efficiency of dye-sensitized solar cells (DSSCs). The results revealed that adding a fluorine substituent on the phenyl group ortho to the cyanoacrylate can enhance the light-harvesting performance in comparison with the unsubstituted one. However, when the two ortho-positions were both substituted by fluorine atoms, the performance of DSSCs was substantially reduced. The reason was mainly ascribed to a distortion from a planar geometry caused by steric hindrance. The π-conjugation was therefore disturbed, and the result led to a substantial reduction of the short-circuit photocurrent density (J_sc). Another effect was found that the open-circuit photovoltage (V_oc) of the doubly substituted derivative was lower than that of the mono-substituted one. The more flexible conformation of the difluoro-substituted dyes induced an undesired nonradiative decay, therefore led to a reduction of open-circuit photovoltage. The phenomenon can be verified by electrochemical impendence spectrum. The non-planar geometry was realized by a computation using the density function theory (DFT) model. The slight blue shift of absorption band was also consistent with the calculated transition energy by a time dependent DFT model.     

The evolution of organic materials for efficient dye-sensitized solar cells

In the past three decades, dye-sensitized solar cells (DSSCs) have gained increased recognition as a potential substitute for inexpensive photovoltaic (PV) devices, and their maximum efficiency has grown from 7% to 14.3%. Recent developments in DSSCs have attracted a plethora of research activities geared at realizing their full potential. DSSCs have seen a revival as the finest technology for specific applications with unique features such as low-cost, non-toxic, colourful, transparent, ease of fabrication, flexibility, and efficient indoor light operation. Several organic materials are being explored and employed in DSSCs to enhance their performance, robustness, and lower production costs to be viable alternatives in the solar cell markets. This review provides a concise summary of the developments in the field over the past decade, with a special focus on the incorporation of organic materials into DSSCs. It covers all elements of the DSSC technology, including practical approaches and novel materials. Finally, the emerging applications of DSSCs, and their future promise are also discussed.     

Synthesis of new perylene imide dyes and their photovoltaic performances in nanocrystalline TiO2 dye-sensitized solar cells

Eight novel perylene imide derivatives were synthesized to determine the effect of the nature of electron donating substituents on the perylene core (ether or N-amino), the position of the carboxylic acid anchoring group and the presence of a fused benzimidazole moiety on the performances of dye-sensitized solar cells. The photovoltaic efficiency under AM1.5 of these new dyes, although not optimized, ranges from 0.2% until 2.3%. We note the importance of the position-anchoring group, which controls the electron injection efficiency. With respect to the excited-state electron donor strength, four O-aryl substituents at the bay position lead to similar effect as two N-piperidinyl groups but with a lower propensity to aggregation and give slightly higher photovoltaic performance than the latter. The benzimidazole unit extends the absorbance of the perylene imide to longer wavelengths, but this effect is lower than introducing charge transfer transition with N-amino substituents. Overall, this work shows that perylene imide remains a promising molecular basis for the future design of new fully organic sensitizers for nanostructured TiO₂ solar cells.     

Synthesis of new di-anchoring organic sensitizer based on quinoxaline acceptor for dye-sensitized solar cells

New quinoxaline-based organic sensitizer bearing di-anchoring group for dye-sensitized solar cells (DSSCs) was synthesized from diethyl 4,5-diaminophthaltate, in which was prepared under mild condition by using Takehito’s method. The synthesized sensitizer was compared with mono-anchoring sensitizer through absorption spectra, emission spectra, J-V curve, and IPCE spectra, indicating the di-anchoring group leads to a noticeable improvement of J_sc value owing to more efficient intramolecular charge transfer and channel number increment.     

Synthesis of sensitizers containing donor cascade of triarylamine and dimethylarylamine moieties for dye-sensitized solar cells

Four triarylamine derivatives (XS6-9) containing N,N-dimethylaryl amine units as secondary electron-donating groups are designed and synthesized. These dyes were applied into nanocrystalline TiO₂ dye-sensitized solar cells through standard operations. For a typical device the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach 93%, with a short-circuit photocurrent density (J_sc) 10.8 mA cm⁻², an open-circuit photovoltage (V_oc) 690 mV, and fill factor (FF) 0.61, which corresponds to an overall conversion efficiency of 4.54%.     

Improvement of dye-sensitized solar cells' performance via co-sensitization of new azo thiazole organic dyes with ruthenium (II) based N-719 dye

Three novel azo thiazole organic dyes, NA-1–3, have been synthesized and utilized as co-sensitizers in dye-sensitized solar cells (DSSCs). These co-sensitizers were designed with a thiazole ring π-bridge that mediates between the diazo (–N = N–) functional group and carboxylic acid anchoring unit. They possess a rod-like molecular structure and exhibit strong UV–vis absorption near 600 nm. Co-sensitization studies were also conducted with the ruthenium complex N719. The co-sensitized DSSCs showed enhanced short-circuit and open-circuit photocurrents (Jsc) and voltages (Voc), resulting in more efficient photovoltaic performance compared to N719 (PCE 7.25%). Electrochemical impedance spectroscopy (EIS) and incident photon to current efficiency (IPCE) were employed to investigate the underlying reasons for these improvements. It was found that co-sensitization effectively reduced electron recombination, resulting in a higher Voc without compromising photocurrent loss.     

Application of indoline dyes attached with strongly electron-withdrawing carboxylated indan-1,3-dione analogues linked with a hexylthiophene ring to dye-sensitized solar cells

An indoline dye attached with a carboxylated indan-1,3-dione moiety linked with a hexylthiophene ring exhibited the highest conversion efficiency among six analogues and D205. This result comes from the bathochromic UV–vis absorption band, suitable energy levels, good stability for redox process, and sufficiently long excited-state lifetime.     

Molecular engineering of organic dyes containing N-aryl carbazole moiety for solar cell

Organic dyes containing N-aryl carbazole moiety are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-25 sensitized cell gave a short circuit photocurrent density (J_sc) of 11.50 mA cm⁻², an open circuit voltage (V_oc) of 0.68 V, a fill factor of 0.66, corresponding to an overall conversion efficiency η of 5.15%, and the maximum incident monochromatic photon-to-current conversion efficiency (IPCE) of 77% at 430 nm.     

Highly efficient new indoline dye having strong electron-withdrawing group for zinc oxide dye-sensitized solar cell

New indoline dye (DN319) having strong electron-withdrawing dicyanovinylidene moiety and octyl group in the terminal rhodanine ring gave higher efficiency than D205, which was known as an excellent organic dye sensitizer. This result is attributed to the bathochromic shift in the UV-vis absorption band and positive shift in the E_ox level of DN319.