Seite - 45 - in Photovoltaic Materials and Electronic Devices

A better stability was ascribed to Os complexes with respect to the Ru case, even thoughthesecomplexesshowedlower lightconversion. Lapides and co-workers, in 2013 [151], tested another element of the eighth group, iron, using terpyridines as ligands in a supramolecular structure with Ru, as a multicomponent film deposed on TiO2. An improved stability of the ruthenium dye was reported, even if these structures have not been tested on DSCsdevices. Morerecently,Duchanois [152] reportedahomoleptic ironcomplex bearingtridentatebis-carbene(CˆNˆC’) ligandsforsensitizationofTiO2 photoanodes (homologous to theRucomplex43a), andcompareditwithabis-tpy ironcomplex (47a,b, Figure 38). A considerable stabilization of 3MLCT state was obtained for the cyclometalatedcomplex,butstill lowperformanceswererecordedwithrespect to thereferencesensitizers. 3.3. Exchange of Metal Center Terpyridine complexes with other metals were reported by Bignozzi’s group, who complexed osmium with tctpy, various bipyridines and pyridylquinoline [148–150]. The idea was to further broaden absorption spectra thanks to Os(II) complexes characterized by high spin-orbit coupling constant that allows the direct population of low energy, spin-forbidden, 3MLCT states. No significant differences in IPCE values were found in the case of the various Os complexes showing values up to 50% at 900 nm and 70% in the visible region. A better stability was ascribed to Os complexes with respect to the Ru case, even though these complexes showed lower light conversion. Lapides and co-workers, in 2013 [151], tested another element of the eighth group, iron, using terpyridines as ligands in a supramolecular structure with Ru, as a multicomponent film deposed on TiO2. An improved stability of the ruthenium dye was reported, even if these structures have not been tested on DSCs devices. More recently, Duchanois [152] reported a homoleptic iron complex bearing tridentate bis-carbene (C^N^C’) ligands for sensitization of TiO2 photoanodes (homologous to the Ru complex 43a), and compared it with a bis-tpy iron complex (47a-b, Figure 38). A considerable stabilization of 3MLCT state was obtained for the cyclometalated complex, but still low performances were recorded with respect to the reference sensitizers. Figure 38. Iron complexes reported by Duchanois [152]. Since platinum(II) complexes usually display an intense charge-transfer absorption band in the visible region, Kwok et al. [153], in 2010, proposed a complex of platinum with tctpy and various alkynyl ancillary ligands, reaching up to 3.6% efficiency. Shinpuku et al. [154] synthesized a series of new complexes of iridium with tpy and biphenylpyridine. Cyclometalated iridium complexes were commonly exploited in light source devices as OLEDs and showed narrower absorption spectra respect to Ruthenium ones due to more energetic MLCT transition. A shorter portion of the solar spectrum was harnessed and a lower Jsc was detected, nevertheless a 2.16% efficiency and long lived excited-state lifetime were reported. The interest for d10 metal ions complexes such as Zn-porphyrines has grown in photonic applications, ranging from OLEDs and LECs to DSCs technologies. Bozic-Weber et al. [155–157] synthesized bis-tpy Zn heteroleptic complexes for TiO2 sensitization. Terpyridines substituted with various anchoring and triphenylamino moieties extended with benzothiadiazole-diphenylamino units gave efficiencies between 0.5 and 1%. Housecroft et al. reviewed sensitizers made of Earth-abundant metals, concerning copper [158] and other d-block metals [159]. 4. p-Type Tpy complexes have been investigated also for the sensitization of p-type semiconductors. In p-type DSCs, the rules for sensitizers design are inverted with respect to classical n-type DSC cells. In fact, in these devices, the excited dye has to inject holes from HOMO to the conduction band of a p-semiconductor [160]. Figure38. IroncomplexesreportedbyDuchanois [152]. Since platinum(II) complexes usually display an intense charge-transfer absorption band in the visible region, Kwok et al. [153], in 2010, proposed a complex of platinum with tctpy and various alkynyl ancillary ligands, reaching upto3.6%efficiency. Shinpuku et al. [154] synthesized a series of new complexes of iridium with tpy andbiphenylpyridine. Cyclometalatediridiumcomplexeswerecommonlyexploited in light source devices as OLEDs and showed narrower absorption spectra respect to Ruthenium ones due to more energetic MLCT transition. A shorter portion of the solar spectrum was harnessed and a lower Jsc was detected, nevertheless a 2.16% efficiencyandlonglivedexcited-state lifetimewerereported. The interest for d10 metal ions complexes such as Zn-porphyrines has grown in photonic applications, ranging from OLEDs and LECs to DSCs technologies. Bozic-Weber et al. [155–157]synthesizedbis-tpyZnheterolepticcomplexes forTiO2 45