Page - 23 - in Photovoltaic Materials and Electronic Devices

Very recently, Kaniyambatti [76] reported a tpy substituted in 4’- with a cyanoacrylic acid moiety via a thiophene bridge (5 in Figure 7). The modification leads again to a hypsochromic shift in the absorption spectrum coupled with a highermolar extinctioncoefficientowing to theextendedpi-conjugationand strong auxochromeresultingfromthethiophenemoiety. Materials 2016, 9, 137 8 of 37 Figure 7. Terpyridine with a cyanoacrylic acid moiety [76]. In 2013, Numata et al. [77] proposed a double anchored tpy bearing a 4-methylstyryl substituted in 4’’- position (6 in Figure 8) in order to extend the π-conjugation and to obtain better charge injection with respect to N749. This complex achieved a higher molar extinction coefficient especially on the π-π* transition, and a better IPCE in the same region, which led to an improved efficiency with respect to BD (η = 11.1% ; TiO2: 25 μm; dye: 0.3 mM acetonitrile / t-butanol 1:1, 24 h + 20 mM CDCA, electrolyte: 0.05 mM I2, 0.1 M LiI, DMPII, 0.2 M t-bupy in CH3CN). Figure 8. 4-Methylstyryl substituted and double-anchored tpy (HIS-2) [77]. In 2011 Yang et al. [78] tested a series of 4,4'-dicarboxy terpyridine bearing a thiophene or a 3,4-ethylenedioxythiophene in 5’’ position (7a-b in Figure 9). The substitution of the latter with a triphenylamino moiety (7c) resulted in better performances with respect to BD tested in the same conditions (η = 8.29% vs. 6.89%; TiO2: 10 μm + 5 μm, dye: 0.3 mM ethanol + 10 mM chenodeoxycholic acid (CDCA), electrolyte: 0.6 M MDPII, 0.5 M t-bupy, 0.05 M I2, 0.1 M LiI in CH3CN), owing to the higher molar extinction coefficients in the high energy region of the spectrum. Substitution with hexyl-EDOT (7b, EDOT: 3,4-ethylenedioxythiophene) afforded even higher efficiency (η = 10.3% with TiO2: 15 + 5 μm). Similar modifications have been taken into consideration by Kimura et al. [79] (7d-g in Figure 9). In the series, structures with hindered hexyloxy-substituted rings resulted in better performances, probably because of the hindrance of alkyl chains towards the electrolyte, thus avoiding the redox couple to interact with titania and considerably reducing the dark current. Among these, the best results were obtained when the electron donor hexyloxy groups on the phenyl ring are in ortho or para positions (7f in Figure 9). Figure7. Terpyridinewithacyanoacrylicacidmoiety [76]. In 2013, Numata et al. [77] proposed a double anchored tpy bearing a 4-methylstyryl substituted in 4”-position (6 in Figure 8) in order to extend the pi-conjugation and to obtain better charge injection with respect to N749. This complex achieved a higher molar extinction coefficient especially on the pi-pi* transition, and a better IPCE in the same region, which led to an improved efficiency with respect to BD (η= 11.1% ; TiO2: 25µm; dye: 0.3 mM acetonitrile / t-butanol 1:1, 24 h + 20 mM CDCA, electrolyte: 0.05 mM I2, 0.1 M LiI, DMPII, 0.2 M t-bupy inCH3CN). Materials 2016, 9, 137 8 of 37 Figure 7. Terpyridine with a cyanoacrylic acid moiety [76]. In 2013, Numata et al. [77] proposed a double anchored tpy bearing a 4-methylstyryl substituted in 4’’- position (6 in Figure 8) in order to extend the π-conjugation and to obtain better charge injection with respect to N749. This complex achieved a higher molar extinction coefficient especially on the π-π* transition, and a better IPCE in the same region, which led to an improved efficiency with respect to BD (η = 11.1% ; TiO2: 25 μm; dye: 0.3 mM acetonitrile / t-butanol 1:1, 24 h + 20 mM CDCA, electrolyte: 0.05 mM I2, 0.1 M LiI, DMPII, 0.2 M t-bupy in CH3CN). Figure 8. 4-Methylstyryl substituted and double-anchored tpy (HIS-2) [77]. In 2011 Yang et al. [78] tested a series of 4,4'-dicarboxy terpyridine bearing a thiophene or a 3,4-ethylenedioxythiophene in 5’’ position (7a-b in Figure 9). The substitution of the latter with a triphenylamino moiety (7c) resulted in better performances with respect to BD tested in the same conditions (η = 8.29% vs. 6.89%; TiO2: 10 μm + 5 μm, dye: 0.3 mM ethanol + 10 mM chenodeoxycholic acid (CDCA), electrolyte: 0.6 M MDPII, 0.5 M t-bupy, 0.05 M I2, 0.1 M LiI in CH3CN), owing to the higher molar extinction coefficients in the high energy region of the spectrum. Substitution with hexyl-EDOT (7b, EDOT: 3,4-ethylenedioxythiophene) afforded even higher efficiency (η = 10.3% with TiO2: 15 + 5 μm). Similar modifications have been taken into consideration by Kimura et al. [79] (7d-g in Figure 9). In the series, structures with hindered hexyloxy-substituted rings resulted in better performances, probably because of the hindrance of alkyl chains towards the electrolyte, thus avoiding the redox couple to interact with titania and considerably reducing the dark current. Among these, the best results were obtained when the electron donor hexyloxy groups on the phenyl ring are in ortho or para positions (7f in Figure 9). Figur 8. 4-Methylstyryl substitutedanddouble-anchoredtpy(HIS-2) [77]. In 2011 Yang et al. [78] tested a series of 4,4'-dicarboxy terpyridine bearing a thiophene or a 3,4-ethylenedioxythiophene in 5” position (7a,b in Figure 9). The substitution of the latter with a triphe ylamino mo ety (7c) resulted in b t er performanc s withrespect to BDtested in thesame conditions (η= 8.29% vs. 6.89%; TiO2: 10µm+5µm,dye: 0.3mMethanol+10mMchenodeoxycholicacid (CDCA), electrolyte: 0.6 M MDPII, 0.5 M t-bupy, 0.05 M I2, 0.1 M LiI in CH3CN), owing to the higher molar extinction coefficients in the high energy region of the spectrum. 23