Seite - 14 - in Photovoltaic Materials and Electronic Devices

TerpyridineandQuaterpyridineComplexes asSensitizers forPhotovoltaicApplications DavideSaccone,ClaudioMagistris,NadiaBarbero,PierluigiQuagliotto, ClaudiaBaroloandGuidoViscardi Abstract: Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allowforachievingmetal-complexeswith lowerbandgaps in themetal-to-ligand transition(MLCT), thusprovidingabetterabsorptionat lowerenergywavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the widerabsorptionof thefirst tricarboxylate terpyridyl ligand-basedcomplex,Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines;othermetalswereusedinsteadofruthenium,andthiocyanateshave beenreplacedbydifferentpinchers inordertoachievecyclometalatedorheteroleptic complexes. The review provides a summary on design strategies, main synthetic routes,opticalandphotovoltaicpropertiesof terpyridineandquaterpyridine ligands appliedtophotovoltaic, andfocusesonn-typeDSCs. Reprinted from Materials. Cite as: Saccone, D.; Magistris, C.; Barbero, N.; Quagliotto, P.; Barolo, C.; Viscardi, G. Terpyridine and Quaterpyridine Complexes as Sensitizers forPhotovoltaicApplications. Materials2016,9, 137. 1. Introduction Dye-sensitized solar cells (DSCs) are photoelectrochemical devices able to convert sunlight into electricity [1]. The architecture and operating principles of these devices have already been extensively reviewed in the literature [2–6], and the photosensitizer represents one of the key components of this device. Different kinds ofsensitizers[3,4]havebeenusedsofar, includingRucomplexes[7],porphyrines[5], phtalocyanines, metal-free dyes [6] (including squaraines [8–10], cyanines [11,12], andpush-pulldyes [13]). Since 1997 [14] the interest in 2,2’:6’,2”-terpyridine (tpy) as ligands in organometallic sensitizers for DSC applications has constantly grown and, in the last three years, more than 80 papers and patents concerning this subject were published. Interest on 2,2’:6’,2”:6”,2”’-quaterpyridines (qtpy) is more recent and has resulted in more than10papers (Figure1). 14