The Rise of Dye‐Sensitized Solar Cells: From Molecular Photovoltaics to Emerging Solid‐State Photovoltaic Technologies

A Dye-Sensitized Sensor for Oxygen Detection under Visible Light

Sensors that can accurately assess oxygen (O2) concentrations in real time are crucial for a wide range of applications spanning personal health monitoring, environmental protection, and industrial process development. Here a high-performance chemiresistive sensor that allows for the rapid detection of O2 at room temperature under visible light illumination is described. Inspired by the operating principles of dye-sensitized solar cells, the chemiresistor is based on a single-walled carbon nanotube-titania hybrid (SWCNT-TiO2) bearing a molecular Re-based photosensitizer [(Pbpy)(CO)3ReBr] (Pbpy = 4,4'-[P(O)(OH)2]2-2,2'-bipyridine). The resulting SWCNT-TiO2-Re composite undergoes photoinduced charge transfer that is sensitive to ppb levels of O2, thereby yielding a rapid and reversible chemiresistive response. Owing to its unique mode of operation and robust components, the sensor shows a high degree of selectivity for O2 over a range of interferants, humidity tolerance, and multimonth benchtop stability. The approach presented herein demonstrates the translatability of concepts in light harvesting to the development of robust, rapid, and low-power sensing technologies.

Novel MoS2/montmorillonite hybrid aerogel encapsulated PEG as composite phase change materials with superior solar-thermal energy harvesting and storage

Phase change materials (PCMs) offer significant advantages in energy conversion and storage by facilitating the storage and release of thermal energy during phase transition processes. However, challenges such as leakage during PCM phase transitions and poor light absorption properties have constrained their application in the field of photothermal energy storage. In this study, Montmorillonite (Mt) and molybdenum disulfide (MoS2) has been used to design and synthesize hybrid aerogels (MoS2/Mt) boasting high mechanical strength and excellent photothermal conversion performance. These aerogels are then used to encapsulate polyethylene glycol (PEG) to prepare composite PCMs with outstanding solar-thermal conversion and storage performances. The results show that the synthesized MoS2/Mt-PEG composite PCMs exhibit high enthalpies of melting and solidification of 169.16 J/g and 170.78 J/g, respectively, while the aerogel supporting material has a high compressive modulus of 1.96 MPa. Moreover, the composite material displayed excellent thermal stability and leakage resistance after undergoing 30 melting-cooling cycles. Furthermore, the incorporation of MoS2 imparted outstanding light absorption properties to the MoS2/Mt-PEG composite, resulting in a high light absorption and photothermal conversion-storage efficiency of 93.4 % and 96.47 %, respectively. Synthesized composite PCMs also demonstrate outstanding performance in solar-thermal-electricity conversion, achieving a voltage output of 458 mV under illumination conditions and maintaining a sustainable voltage output even after removing the light source. Thus, the composite PCMs prepared in this work can meet the requirements of high enthalpy, effective leakage prevention, efficient solar-thermal conversion and solar-thermal-electricity conversion performance, thereby presenting potential applications in practical solar energy collection, conversion, and storage.

Electrodeposited PEDOT/Nafion as Catalytic Counter Electrodes for Cobalt and Copper Bipyridyl Redox Mediators in Dye-Sensitized Solar Cells

PEDOT-based counter electrodes for dye-sensitized solar cells (DSSCs) are generally prepared by electrodeposition, which produces polymer films endowed with the best electrocatalytic properties. This translates in fast regeneration of the redox mediator, which allows the solar cell to sustain efficient photoconversion. The sustainable fabrication of DSSCs must consider the scaling up of the entire process, and when possible, it should avoid the use of large amounts of hazardous and/or inflammable chemicals, such as organic solvents for instance. This is why electrodeposition of PEDOT-based counter electrodes should preferably be carried out in aqueous media. In this study, PEDOT/Nafion was electrodeposited on FTO and comparatively evaluated as a catalytic material in DSSCs based on either cobalt or copper electrolytes. Our results show that the electrochemical response of PEDOT/Nafion toward Co(II/III-) or Cu(I/II)-based redox shuttles was comparable to that of PEDOT/ClO4 and significantly superior to that of PEDOT/PSS. In addition, when tested for adhesion, PEDOT/Nafion films were more stable for delamination if compared to PEDOT/ClO4, a feature that may prove beneficial in view of the long-term stability of solar devices.

Transition Metal Coordination Compounds as Novel Materials for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are a novel solar cell alternative characterized by lower toxicity by using coordination transition metal compounds while providing high performance benchmarks, such as power conversion efficiency. Particular attention should be paid to compounds containing Cu, which can act both as dyes and as redox mediators, even though compounds relying on other transition metals are also frequently reported. In this paper, examples of compounds containing transition metals in combination with several ligands are presented, and their basic photovoltaic parameters are given.

Chlorophylls: A Personal Snapshot

Chlorophylls provide the basis for photosynthesis and thereby most life on Earth. Besides their involvement in primary charge separation in the reaction center, they serve as light-harvesting and light-sensing pigments, they also have additional functions, e.g., in inter-system electron transfer. Chlorophylls also have a wealth of applications in basic science, medicine, as colorants and, possibly, in optoelectronics. Considering that there has been more than 200 years of chlorophyll research, one would think that all has been said on these pigments. However, the opposite is true: ongoing research evidenced in this Special Issue brings together current work on chlorophylls and on their carotenoid counterparts. These introductory notes give a very brief and in part personal account of the history of chlorophyll research and applications, before concluding with a snapshot of this year's publications.

Solid-state dye-sensitized solar cells using polymeric hole conductors

The present review presents the application of electronically conducting polymers (conducting polymers) as hole conductors in solid-state dye solar cells (S-DSSCs). At first, the basic principles of dye solar cell operation are presented. The next section deals with the principles of electrochemical polymerisation and its photoelectrochemical variety, the latter being an important, frequently-used technique for generating conducting polymers and hole conductors in DSSCs. Finally, two varieties of S-DSSC configurations, those of dry S-DSSC and of S-DSSCs incorporating a liquid electrolyte, are discussed.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.

On the Use of PEDOT as a Catalytic Counter Electrode Material in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) emerged in the early 1990s as a promising alternative to the classic silicon-based solar cell due to their unique combination of low cost, ease of fabrication, color palette for building integration, and high efficiency in indoor applications. This review article describes the fabrication and the properties of poly (3,4-ethylenedioxythiophene) (PEDOT)-based catalytic counter electrodes (CEs) for DSSCs. In particular, the electrochemical reactivity PEDOT CEs used in conjunction with alternative redox mediators for DSSCs is outlined. Among alternative redox shuttles, cobalt and copper complexes, as well as totally organic thiolate/disulfide, have been considered. Finally, PEDOT can also be used as a hole conductor material in electrolyte-free solid-state dye-sensitized solar cells. This review clearly shows that the progress in DSSCs development is strongly linked to the introduction of PEDOT as a new counter electrode material.