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To develop photosensitizers with high open-circuit photovoltage (Voc) is a crucial strategy to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, we show a judiciously tailored organic photosensitizer, coded MS5, featuring the bulky donor N-(2',4'-bis(dodecyloxy)-[1,1'-biphenyl]-4-yl)-2',4'-bis(dodecyloxy)-N-phenyl-[1,1'-biphenyl]-4-amine and the electron acceptor 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid. Employing MS5 with a copper (II/I) electrolyte enables a dye-sensitized solar cell (DSC) to achieve a strikingly high Voc of 1.24 V, with the Voc deficit as low as 130 mV and an ideality factor of merely 1.08. The co-sensitization of MS5 with the wider spectral-response dye XY1b produces a highly efficient and stable DSC with the PCE of 13.5% under standard AM1.5 G, 100 mW cm−2 solar radiation. Remarkably, the co-sensitized solar cell (active area of 2.8 cm2) presents a record PCE of 34.5% under ambient light, rendering it very attractive as an ambient light harvesting energy source for low power electronics. Designing photo-sensitisers with high open-circuit voltage (Voc) is desirable to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, the authors employ a judiciously tailored organic sensitiser MS5 with copper electrolyte to achieve a Voc of 1.24 V, and recorded PCE of 34.5% under ambient light. [ABSTRACT FROM AUTHOR]

Dye‐sensitized solar cells (DSCs) based on copper(II/I) redox mediators have recently achieved notable performance progress through tailoring the ligand structure of the copper complexes, exploiting cosensitization, and introducing an advanced device structure. In order to further improve the power conversion efficiency (PCE), it is imperative to develop wide spectral‐response photosensitizers compatible with the copper(II/I) redox mediators while attaining a high Voc. Herein, a blue photosensitizer coded R7 is reported, which is purposely designed for highly efficient DSCs with copper‐based electrolytes. R7 features a strong electron‐donating segment of 9,19‐dihydrobenzo[1′,10′ ]phenanthro[3′,4′:4,5]thieno[3,2‐b]benzo[1,10]phenanthro[3,4‐d]thiophene conjugated with a bulky auxiliary donor N‐(2,4′‐bis(hexyloxy)‐[1,1′‐biphenyl]‐4‐yl)‐2,4′‐bis(hexyloxy)‐N‐methyl‐[1,1′‐biphenyl]‐4‐amine and the electron acceptor 4‐(7‐ethynylbenzo[c][1,2,5]thiadiazol‐4‐yl)benzoic acid. The blue dye R7 with bulkier auxiliary donor moiety in the DSC largely outperforms the reference dye R6, which has a smaller bis(4‐(hexyloxy)phenyl)amine donor unit. Transient absorption spectroscopy and electrochemical impedance spectroscopy measurements show that the R7 based DSC has a higher charge separation yield, a higher charge collection efficiency, and lower charge recombination with the copper electrolyte than the R6 based counterpart. A cosensitized system of R7 and Y123 for the DSC presents an outstanding PCE of 12.7% and retains 90% of its initial value after 1000 h of light soaking under 1 sun at 45 °C. [ABSTRACT FROM AUTHOR]

Dye‐sensitized solar cells (DSSCs) based on CuII/I bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open‐circuit voltages (VOC, more than 1 V). However, their short‐circuit photocurrent density (JSC) has remained modest. Increasing the JSC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO2 film and fast regeneration by the CuI complex. Herein, we report two new D‐A‐π‐A‐featured sensitizers termed HY63 and HY64, which employ benzothiadiazole (BT) or phenanthrene‐fused‐quinoxaline (PFQ), respectively, as the auxiliary electron‐withdrawing acceptor moiety. Despite their very similar energy levels and absorption onsets, HY64‐based DSSCs outperform their HY63 counterparts, achieving a power conversion efficiency (PCE) of 12.5 %. PFQ is superior to BT in reducing charge recombination resulting in the near‐quantitative collection of photogenerated charge carriers. [ABSTRACT FROM AUTHOR]

Four organic donor-π-bridge-acceptor dyes containing phenothiazine as a spacer and cyanoacrylic acid as an acceptor were synthesized and tested as sensitizers in dye-sensitized solar cells (DSCs). The influence of iodide- and cobalt-based redox electrolytes on the photovoltaic device performance was investigated. In these new dyes, systematic π-conjugation was extended by inserting one or two phenothiazine moieties and investigated within the context of the resulting photoinduced charge-transfer properties. A detailed investigation, including transient absorption spectroscopy and quantum chemical methods, provided important information on the role of extended π-conjugation on the photophysical properties and photovoltaic device performance. Overall, the results showed that the extension of π-conjugation by one phenothiazine unit resulted in the best device performance owing to reduced recombination rates, whereas extension by two phenothiazine units reduced dye adsorption on TiO2 probably owing to the increase in molecular size. The performance of the dyes in DSCs was found to be a complex interaction between dye structure and size. [ABSTRACT FROM AUTHOR]

Ruthenium und Co: Ruthenium(II) ‐ Komplexe sind nach wie vor die „heißesten Kandidaten“ für Farbstoffsolarzellen, doch derzeit bekannte Ru ‐ Sensibilisatoren sind nicht mit CoII/III ‐ Elektrolyten kompatibel. Der Effekt einer Oberflächenisolierung auf die Leistungsfähigkeit einer Zelle wurde durch den Vergleich zweier cyclometallierter RuII ‐ Komplexe studiert. Der Ansatz zeigt ein allgemeines Prinzip für beispiellose Effizienzen bei der Kombination von RuII ‐ Sensibilisatoren mit einem Cobalt ‐ Elektrolyt. [ABSTRACT FROM AUTHOR]

Summary: The high molar extinction coefficient heteroleptic ruthenium dye, NaRu(4,4′-bis(5-(hexylthio)thiophen-2-yl)-2,2′-bipyridine) (4-carboxylic acid-4′-carboxylate-2,2′-bipyridine) (NCS)2, exhibits certified 5% electric power conversion efficiency at AM 1.5 solar irradiation (100mWcm−2) in a solid-state dye-sensitized solar cell using 2,2′,7,7′-tetrakis-(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD) as the organic hole-transporting material. This demonstration elucidates a class of photovoltaic devices with potential for low-cost power generation. [Copyright &y& Elsevier]

Dye-sensitized solar cells (DSCs) have achieved impressive conversion efficiencies for solar energy of over 11% with an electrolyte that contains triiodide/iodide as a redox couple. Although triiodide/iodide redox couples work efficiently in DSCs, they suffer from two major disadvantages: electrolytes that contain triiodide/iodide corrode electrical contacts made of silver (which reduces the options for the scale up of DSCs to module size) and triiodide partially absorbs visible light. Here, we present a new disulfide/thiolate redox couple that has negligible absorption in the visible spectral range, a very attractive feature for flexible DSCs that use transparent conductors as current collectors. Using this novel, iodide-free redox electrolyte in conjunction with a sensitized heterojunction, we achieved an unprecedented efficiency of 6.4% under standard illumination test conditions. This novel redox couple offers a viable pathway to develop efficient DSCs with attractive properties for scale up and practical applications. [ABSTRACT FROM AUTHOR]

This article reports that conversion of light into electricity in dye-sensitized solar cells is initiated by the charge injection from an electronically excited dye molecule into the conduction band of a wide band gap oxide semiconductor. Because of their successful use in such devices, ruthenium (II) polypyridyl complex dyes adsorbed on nanocrystalline titanium dioxide films have been regarded as model systems for the experimental study of the ultrafast dynamics of interfacial light-induced electron transfer. Yet, the complex kinetic behavior observed for the charge injection process in this case has prevented the development of a satisfying kinetic model and has led to often contradicting conclusions.

Nanocrystalline dye-sensitized solar cells (DSCs) are attracting considerable academic and industrial interest as low-cost, high-efficiency alternatives to the conventional solid p-n junction photovoltaic devices. A record of 10.6% total power conversion efficiency has recently been reached using a liquid organic electrolyte based on the iodide/triiodide redox couple. The recentachievement of long-term thermal stability by molecular-scale interface engineering has undoubtedly injected new momentum into this field. However, the sealing of volatile electrolytes in large scale modules still remains a critical issue in view of the practical application.

TwoD−π–A dyes based on the dithieno[3,2-b:2′,3′-d]pyrrole π-bridge(DTP) were synthesized, characterized using UV–vis absorptionspectroscopy and electrochemistry, modeled using quantum chemicalcalculations, and used as sensitizers in dye-sensitized solar cells(DSCs). The photoelectrochemical properties and DSC performance arethoroughly compared with their cyclopenta[1,2-b:5,4-b′]dithiophene (CPDT) analogues. The use of DTP resultsin a small increase in the zero–zero transition energy reflectingthe higher lying lowest unoccupied molecular orbital that is commonlyreported for DTP relative to CPDT systems. This increased opticalgap manifests in slightly blue-shifted incident photon-to-collectedelectron conversion efficiency (IPCE) responses; however, increasedopen-circuit photovoltage values and improved charge-transfer kineticsrelative to the CPDT systems result in comparable power conversionefficiencies. The present report highlights the potential of DTP forthe development of tailored sensitizers employing stronger acceptors. [ABSTRACT FROM AUTHOR]

To improve their efficiency beyondthe state-of-the-art, D−π–Adyes must display increased spectral breadth and account for the physicallimitations observed in the dye-sensitized solar cells. In particular,they should be designed to control the electron-transfer processesthat ensure efficient dye-regeneration and prevent undesired electronrecombination. In this article, the electronic and steric propertiesof a fluorene donor are engineered to meet all these requirements.This elegant donor is featured along with a cyclopentadithiophenebridge and a cyanoacrylic acid acceptor in JF419. A thoroughcomparison with Y123and C218demonstratesthe relevance of the design. Relative to conventional donors, thefluorene construct described here enhances the light-harvesting properties,because of its exceptional electron-donating character. The functionalitiesused to induce the electronic push through the D−π–Astructure also provide the dye with favorable steric properties. Indeed,the substitution around the fluorene core adequately insulates theTiO2surface from the electrolyte, which prevents back-recombinationand prolongs the electron lifetime in the semiconductor. Furthermore,compared to analogous dyes, JF419maintains nearly quantitativeregeneration efficiency, despite the lower regeneration driving force.The root of this observation is contributed to a significantly moredelocalized hole in the photo-oxidized JF419• +, which is highlighted through transient absorptionspectroscopy and quantum chemical calculations. The design principlesestablished are relevant to the development of more comprehensivesensitizers, as evidenced by the 10.3% efficiency obtained in cobalt-basedliquid dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]