Page - 46 - in Photovoltaic Materials and Electronic Devices

sensitization. Terpyridinessubstitutedwithvariousanchoringandtriphenylamino moieties extended with benzothiadiazole-diphenylamino units gave efficiencies between0.5%and1%. Housecroftetal. reviewedsensitizersmadeofEarth-abundant metals, concerningcopper [158]andotherd-blockmetals [159]. 4. p-Type Tpy complexes have been investigated also for the sensitization of p-type semiconductors. Inp-typeDSCs, therules forsensitizersdesignare invertedwith respect toclassicaln-typeDSCcells. In fact, in thesedevices, theexciteddyehas to injectholes fromHOMOtotheconductionbandofap-semiconductor [160]. Ji et al., in 2013 [161], proposed a cyclometalated (NˆCˆN’)-(NˆN’ˆN”) Ru[II] chromophore tosensitizeNiO(48, Figure39). TheNˆCˆN’ ligandwasemployedas anchoringmoiety,while the tpy ligandwasfunctionalized in the4’positionwitha substituted naphthalenediimide (NDI) in order to withdraw electrons from the NiO surface. This dye was studied by femtosecond transient absorption spectroscopy, and results showed aslower chargerecombination in the NDI-substitutedcomplex. PeryleneimideshavebeenrecentlyusedbySariola-Leikasetal.[162]asbridgegroups toobtainsupramolecularstructures forTiO2 sensitization insolidstatedevices. Materials 2016, 9, 137 25 of 37 Ji et al., in 2013 [161], proposed a cyclometalated (N^C^N’)-(N^N’^N’’) Ru[II] chromophore to sensitize NiO (48, Figure 39). The N^C^N’ ligand was employed as anchoring moiety, while the tpy ligand was functionalized in the 4’ position with a substituted naphthalenediimide (NDI) in order to withdraw electrons from the NiO surface. This dye was studied by femtosecond transient absorption spectroscopy, and results showed a slower charge recombination in the NDI-substituted complex. Perylene imides have been recently used by Sariola-Leikas et al. [162] as bridge groups to obtain supramolecular structures for TiO2 sensitization in solid state devices. Figure 39. NDI-Tpy proposed by Ji et al. [161]. In 2014 both Constable [163] and Wood [164] proposed heteroleptic tpy complexes for sensitization of p-type semiconductors. The latter used a triphenyl amino moiety as anchoring donor group to increase the hole injection achieving efficiencies in pDSCs between 0.07 and 0.09 (49, Figure 40). Both bis-tpy and phenylbipy-tpy complexes were investigated showing better performances with iodine electrolyte with respect to the Co-based one, which was ascribed to high charge recombination with NiO. Figure39. NDI-TpyproposedbyJi et al. [161]. In 2014 both C stable [163] and Wood [164] proposed heteroleptic tpy c mpl xes for sens tiza of p-type semiconductors. The latt r used a triphenyl amino moiety as a choring don r group to increase the hole injection achi ving effici ncies in pDSCs b tween 0.07 and 0.09 (49, Figure 40). Both bis- py and phenylbipy-tpy complexes were investigated showing better performances with iodine electrolyte with respect to the Co-based one, which was ascribed to high chargerecombinationwithNiO. 46