Scalable Low‐Cost SnS2 Nanosheets as Counter Electrode Building Blocks for Dye‐Sensitized Solar Cells

A new type of semitransparent SnS₂ nanosheet (NS) films were synthesized using a simple and environmentally friendly solution‐processed approach, which were subsequently used as a counter electrode (CE) alternative to the noble metal Pt for triiodide reduction in dye‐sensitized solar cells (DSSCs). The resultant SnS₂‐based CE with a thickness of about 300 nm exhibited excellent electrochemical catalytic activity for catalyzing the reduction of triiodide and demonstrated comparable power conversion efficiency of 7.64 % with that of expensive Pt‐based CE in DSSCs (7.71 %). When functionalized with a small amount of carbon nanoparticles, the SnS₂ NS‐based CE showed even better performance of 8.06 % than Pt under the same conditions. Considering the facile fabrication method, optical transparency, low cost, and remarkable catalytic property, this study on SnS₂ NSs may shed light on the large‐scale production of electrocatalytic electrode materials for low‐cost photovoltaic devices.     

Efficient Counter Electrode Manufactured from Ag2S Nanocrystal Ink for Dye‐Sensitized Solar Cells

It is generally believed that silver or silver‐based compounds are not suitable counter electrode (CE) materials for dye‐sensitized solar cells (DSSCs) due to the corrosion of the I^?/I₃^? redox couple in electrolytes. However, Ag₂S has potential applications in DSSCs for catalyzing I₃^? reduction reactions because of its high carrier concentration and tiny solubility product constant. In the present work, CE manufactured from Ag₂S nanocrystals ink exhibited efficient electrocatalytic activity in the reduction of I₃^? to I^? in DSSCs. The DSSC consisting of Ag₂S CE displayed a higher power conversion efficiency of 8.40 % than that of Pt CE (8.11 %). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiated stability. The simple composition, easy preparation, stable chemical property, and good catalytic performance make the developed Ag₂S CE as a promising alternative to Pt CE in DSSCs.     

Fabrication of Mesoporous CoS2 Nanotube Arrays as the Counter Electrodes of Dye‐Sensitized Solar Cells

Mesoporous cobalt sulfide nanotube arrays on FTO‐coated glass were synthesized by combining three simple technologies: the selective etching of ZnO sacrificial templates, mesoporous Co₃O₄ formation from cobalt‐chelated chitosan, and ion‐exchange reaction (IER). The mesoporous Co₃O₄ nanotubes composed of the Co₃O₄ nanoparticles possess a high surface area and are taken advantage for further removal of templates and IER. The morphologies and crystal structures of the CoS₂ nanotube arrays were characterized by SEM, TEM, and XRD analyses. Their electrocatalytic properties were determined by electrochemical analyses including cyclic voltammetry measurements and Tafel polarization. The DSSCs assembled with a CoS₂ counter electrode achieved a power conversion efficiency of 6.13 %, which was comparable to that of the DSSC with the Pt counter electrode (6.04 %). This indicates that the mesoporous CoS₂ nanotube array can be a low‐cost and efficient alternative for the reduction of electrolytes in DSSCs.     

A Graphene Composite Material with Single Cobalt Active Sites: A Highly Efficient Counter Electrode for Dye‐Sensitized Solar Cells

The design of catalysts that are both highly active and stable is always challenging. Herein, we report that the incorporation of single metal active sites attached to the nitrogen atoms in the basal plane of graphene leads to composite materials with superior activity and stability when used as counter electrodes in dye‐sensitized solar cells (DSSCs). A series of composite materials based on different metals (Mn, Fe, Co, Ni, and Cu) were synthesized and characterized. Electrochemical measurements revealed that CoN₄/GN is a highly active and stable counter electrode for the interconversion of the redox couple I^?/I₃^?. DFT calculations revealed that the superior properties of CoN₄/GN are due to the appropriate adsorption energy of iodine on the confined Co sites, leading to a good balance between adsorption and desorption processes. Its superior electrochemical performance was further confirmed by fabricating DSSCs with CoN₄ /GN electrodes, which displayed a better power conversion efficiency than the Pt counterpart.     

Enhanced Electrocatalytic Performance of a Porous g‐C3N4/Graphene Composite as a Counter Electrode for Dye‐Sensitized Solar Cells

A porous graphitic carbon nitride (g‐C₃N₄)/graphene composite was prepared by a simple hydrothermal method and explored as the counter electrode of dye‐sensitized solar cells (DSCs). The obtained g‐C₃N₄/graphene composite was characterized by XRD, SEM, TEM, FTIR spectroscopy, and X‐ray photoelectron spectroscopy. The results show that incorporating graphene nanosheets into g‐C₃N₄ forms a three‐dimensional architecture with a high surface area, porous structure, efficient electron‐transport network, and fast charge‐transfer kinetics at the g‐C₃N₄/graphene interfaces. These properties result in more electrocatalytic active sites and facilitate electrolyte diffusion and electron transport in the porous framework. As a result, the as‐prepared porous g‐C₃N₄/graphene composite exhibits an excellent electrocatalytic activity. In I^?/I₃^? redox electrolyte, the charge‐transfer resistance of the porous g‐C₃N₄/graphene composite electrode is 1.8 Ω cm², which is much lower than those of individual g‐C₃N₄ (70.1 Ω cm²) and graphene (32.4 Ω cm²) electrodes. This enhanced electrocatalytic performance is beneficial for improving the photovoltaic performance of DSCs. By employing the porous g‐C₃N₄/graphene composite as the counter electrode, the DSC achieves a conversion efficiency of 7.13 %. This efficiency is comparable to 7.37 % for a cell with a platinum counter electrode.     

A Soft‐Template‐Conversion Route to Fabricate Nanopatterned Hybrid Pt/Carbon for Potential Use in Counter Electrodes of Dye‐Sensitized Solar Cells

Hybrid Pt(platinum)/carbon nanopatterns with an extremely low loading level of Pt catalysts derived from block copolymer templates as an alternative type of counter electrodes (CEs) in dye‐sensitized solar cells (DSSCs) are proposed. DSSCs employing hybrid Pt/carbon with tailored configuration as CEs exhibit higher short‐circuit current and conversion efficiencies as well as stability with a lapse of time compared with conventional cells on the basis of sputtered Pt thin films, evidencing that the new class of hybrid nanostructures possess high potential for cost‐effective electrodes in energy conversion devices.

     

Benzimidazole/Pyridoimidazole‐Based Organic Sensitizers for High‐Performance Dye‐Sensitized Solar Cells

A new series of benzimidazole ( BIm )‐based dyes ( SC32 and SC33 ) and pyridoimidazole‐( PIm ) based dyes ( SC35, SC36N and SC36 ) were synthesized as sensitizers for dye‐sensitized solar cells (DSSCs). The N‐substituent and C‐substituent at the BIm and PIm cores were found to be the dominating factor in determining the electronic properties of the dyes and their DSSCs performance. The efficiency of BIm ‐based dyes ( SC35 and SC36 ) was found to be higher than that of the PIm ‐based dyes ( SC32 and SC33 ) due to better light harvesting. The C‐substituents in SC36 , a 4‐hexylloxybenzene and a hexyl chain, are beneficial to dark current suppression, and hence SC36 achieves the best efficiency of 7.38 % (≈85 % of N719 ). The two BIm dyes have better cell efficiencies than their congeners with a bithiophene entity between the BIm and the anchor due to better light harvesting of the former.     

Thieno[3,4‐b]thiophene‐Based Organic Dyes for Dye‐Sensitized Solar Cells

New dipolar sensitizers containing an ethyl thieno[3,4‐b]thiophene‐2‐carboxylate (ETTC) entity in the conjugated spacer have been synthesized in two isomeric forms. These compounds were used as the sensitizers of n‐type dye‐sensitized solar cells (DSSCs). The best conversion efficiency (5.31 %) reaches approximately 70 % of the N719‐based (7.41 %) DSSC fabricated and measured under similar conditions. The ETTC‐containing compounds exhibit a bathochromic shift of the absorption compared to their thiophene congeners due to the quinoid effect, however, charge‐trapping at the ester group of ETTC was found to jeopardize the electron injection and lower the cell efficiency. Charge trapping is alleviated as the ester group of ETTC is replaced with a hydrogen atom, as evidenced from the theoretical computation.     

Tropolone as a High‐Performance Robust Anchoring Group for Dye‐Sensitized Solar Cells

A tropolone group has been employed for the first time as an anchoring group for dye‐sensitized solar cells (DSSCs). The DSSC based on a porphyrin, YD2‐o‐C8T, with a tropolone moiety exhibited a power‐conversion efficiency of 7.7 %, which is only slightly lower than that observed for a reference porphyrin, YD2‐o‐C8 , with a conventional carboxylic group. More importantly, YD2‐o‐C8T was found to be superior to YD2‐o‐C8 with respect to DSSC durability and binding ability to TiO₂. These results unambiguously demonstrate that tropolone is a highly promising dye‐anchoring group for DSSCs in terms of device durability as well as photovoltaic performance.     

Brookite TiO2 Nanoparticle Films for Dye‐Sensitized Solar Cells

Brookite TiO₂ nanoparticles have been synthesized at low temperature by a soft solution growth method and have been used as building blocks to prepare pure brookite nanoparticle porous films. The film brookite structure was confirmed by XRD and Raman spectroscopy. By spectrophotometry, it was shown that the films had a direct band gap of 3.4 eV. After sensitization by the N719 dye, efficient cells have been produced. A best overall conversion efficiency of 5.97 %, without a scattering layer, was found for the larger TiO₂ starting nanoparticles. The cell open‐circuit voltage was improved compared with that of anatase cells and a lower electron diffusion coefficient was found in the photoanodes made of smaller brookite particles. Lanthanum‐doped brookite nanoparticle films were also studied. They showed a marked decreased in the amount of dye loading, and hence, the solar cells had a reduced current density that was not compensated for by the increased open‐circuit voltage of the cells.     

Osmium Polypyridyl Complexes and Their Applications to Dye‐Sensitized Solar Cells

Dye‐sensitized solar cells (DSSCs) have received much attention in recent years owing to their efficient conversion of sunlight to electricity. DSSCs became successful alternatives to silicon photovoltaic devices by virtue of their low fabrication costs and easy preparation methods. In DSSCs the dye plays the key role. This review summarizes the applications of osmium sensitizers in DSSCs. We also briefly discussed their synthesis and the effect of various electrolyte systems on device efficiencies.     

High Molar Extinction Coefficient Organic Sensitizers for Efficient Dye‐Sensitized Solar Cells

We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene–vinylene–thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK‐113 ‐sensitized cell gave a short circuit photocurrent density (J_sc) of 17.61 mA cm^?2, an open‐circuit voltage (V_oc) of 0.71 V, and a fill factor (FF) of 72 %, corresponding to an overall conversion efficiency (η) of 9.1 %. The incident monochromatic photo‐to‐current conversion efficiency (IPCE) of JK‐113 exceeds 80 % over the spectral region from 400 to 640 nm, reaching its maximum of 93 % at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar‐cell devices based on the sensitizer JK‐113 in conjunction with a volatile electrolyte and a solvent‐free ionic liquid electrolyte gave high conversion efficiencies of 9.1 % and 7.9 %, respectively. The JK‐113 ‐based solar cell fabricated using a solvent‐free ionic liquid electrolyte showed excellent stability under light soaking at 60 °C for 1000 h.     

Recent Developments in Dye‐Sensitized Solar Cells

The knowledge of dye‐sensitized solar cells (DSCs) has expanded considerably in recent years. They are multiparameter and complex systems that work only if various parameters are tuned simultaneously. This makes it difficult to target to a single parameter to improve the efficiency. There is a wealth of knowledge concerning different DSC structures and characteristics. In this review, the present knowledge and recent achievements are surveyed with emphasis on the more promising cell materials and designs.     

Ruthenium and Osmium Complexes That Bear Functional Azolate Chelates for Dye‐Sensitized Solar Cells

The preparation of sensitizers for dye‐sensitized solar cells (DSSCs) represents an active area of research for both sustainability and renewable energy. Both Ru^II and Os^II metal sensitizers offer unique photophysical and electrochemical properties that arise from the intrinsic electronic properties, that is, the higher propensity to form the lower‐energy metal‐to‐ligand charge‐transfer (MLCT) transition, and their capability to support chelates with multiple carboxy groups, which serve as a bridge to the metal oxide and enable efficient injection of the photoelectron. Here we present an overview of the synthesis and testing of these metal sensitizers that bear functional azolate chelates (both pyrazolate and triazolate), which are capable of modifying the metal sensitizers in a systematic and beneficial manner. Basic principles of the molecular designs, the structural relationship to the photophysical and electrochemical properties, and performances of the as‐fabricated DSSCs are highlighted. The success in the breakthrough of the synthetic protocols and potential applications might provide strong stimulus for the future development of technologies such as DSSCs, organic light‐emitting diodes, solar water splitting, and so forth.