ABSTRACT
Toward the extension of the light-harvesting region of sensitizers in dye-sensitized solar cells (DSSCs), two ethynyl-linked porphyrin trimers were synthesized and investigated. The zincfreebasezinc trimer (ZnFbAZn) showed an absorption maximum at a longer wavelength than the all-zinc trimer (ZnZnAZn), although the energy level of ZnFbAZn was lower than that of ZnZnAZn. The DSSCs using these trimers showed spectral sensitivities up to 900 nm. Reflecting the energy levels of these trimers, the DSSC using ZnZnAZn showed better performance than that using ZnFbAZn. After the optimization of cell fabrication conditions, the photoelectric conversion efficiency η of the DSSC using ZnZnAZn reached 3.17%. The larger TiO2 nanoparticles (ca. 37 nm) than the conventional cases (ca. 13 nm) were found to be preferable in this case, due to high molar extinction coefficients of the porphyrin trimers.
ABSTRACT
Ethynyl-linked porphyrin hetero-dimers substituted by a series of electron donors, namely, bis(4-methoxyphenyl)amino (BMPA), bis(4-tert-butylphenyl)amino (BTBPA) and 3,6-di-tert-butylcarbazol-9-yl (DTBC) as well as a reference dimer with a non-donor moiety (3,5-di-tert-butylphenyl, DTBP) have been synthesized to systematically investigate the influence of donor introduction on the photovoltaic performances of near-IR dye-sensitized solar cells (DSCs) with these sensitizers incorporated. Despite the expected bathochromic shift and intensification of long-wavelength absorption bands as well as elevated LUMO levels and thus increased electron injection driving forces, the substitution of diphenylamino groups (BMPA and BTBPA) with stronger electron-donating abilities gave rise to surprising mediocrity in the short-circuit photocurrent densities (J(sc)), leading to overall energy conversion efficiencies in the order BMPA (3.94%) < DTBP (4.57%) < BTBPA (4.83%) < DTBC (5.21%). A study of the in situ fluorescent behavior of these sensitizers revealed that for all the sensitizers, excited-state lifetimes were significantly shortened in the simulated DSC environment compared to those in a free solution. BMPA showed the shortest intrinsic in situ lifetime while DTBC showed the longest one. These results were correlated with the photovoltaic performances, which is required for a better understanding and further design of porphyrin array sensitizers.
ABSTRACT
N-fused carbazole-zinc porphyrin-free-base porphyrin triad featuring an ethynyl-linkage was synthesized; efficient sensitization as long as 900 nm was demonstrated and an overall light-to-electricity conversion efficiency of 5.21% was achieved under AM 1.5 G one sun illumination.
