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.     

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.     

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.     

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.     

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.     

New D-π-A dyes for efficient dye-sensitized solar cells

Functional organic dyes have promising prospect in dye-sensitized solar cells as a crucial element, of which sensitizers based on donor-π-acceptor are the most important dyes. On the basis of the structures of the aromatic amine donors such as triphenylamine and indoline, this paper reviews the photoelectric conversion properties of organic sensitizers since 2008, and highlights research work in our laboratory in this area.     

Phenoxazine dyes for dye-sensitized solar cells: relationship between molecular structure and electron lifetime

A series of metal-free organic dyes with a core phenoxazine chromophore have been synthesized and tested as sensitizers in dye-sensitized solar cells. Overall conversion efficiencies of 6.03-7.40% were reached under standard AM 1.5G illumination at a light intensity of 100 mW cm(-2) . A clear trend in electron lifetime could be seen; a dye with a furan-conjugated linker showed a shorter lifetime relative to dyes with the acceptor group directly attached to the phenoxazine. The addition of an extra donor unit, which bore insulating alkoxyl chains, in the 7-position of the phenoxazine could increase the lifetime even further and, together with additives in the electrolyte to raise the conduction band, an open circuit voltage of 800 mV could be achieved. From photoelectron spectroscopy and X-ray absorption spectroscopy of the dyes adsorbed on TiO(2) particles, it can be concluded that the excitation is mainly of cyano character (i.e., on average, the dye molecules are standing on, and pointing out, from the surface of TiO(2) particles).     

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.     

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.     

Recent research progress for upconversion assisted dye-sensitized solar cells

Upconversion(UC) technology makes it possible to harvest infrared(IR) light from the sun and has increasingly been employed in recent years to improve the efficiency of solar cells. The progress in the area concerns both research on fundamental principles and processes of UC and technologies of device fabrication. Significant increase of important solar cell parameters, like short-circuit photocurrent density and open-circuit photovoltage as well as the total photon-to-current efficiency, has been accomplished. We here review the research published during the last few years in the area, in particular we consider the two most cherished techniques, namely the incorporation of upconverting nanophosphors directly into the photoanodes of the solar cells and the introduction of plasmonic metal nanoparticles co-existing with the UC particles. Other ways to achieve strong field enhancement,and the use of the non-linear nature of UC, is to apply microlenses, with or without assisting plasmonic excitation. Further enhanced UC action has been demonstrated by broad band and effective harvesting by organic IR antennas, with subsequent mediation by an intermediate nanoshell of the energy into the upconverting core. Codoping, nanohybrid and layer-by-layer technologies involving upconverting particles as well as the use of upconverting nanoparticles in hole-transport and electrolyte layers, tested in recent works, are also reviewed. While most of these technologies employ upconverting rare earth metals for sequential photon absorption, the main alternative technique, namely triplet-triplet annihilation UC using organic materials, is also reviewed. It is our belief that all these approaches will be further much researched in the near future, with potentially great impact on solar cell technology.