In this work, we present the construction and photovoltaic response of porphyrin-sensitized solar cells containing Toray^TM/TGP-H-060 carbon – modified indium-doped tin oxide (ITO) cathodes (ITO/C), as a viable alternative for substituting platinum oxides – modified ITO cathodes (ITO/PtO_x), which are traditionally employed for designing dye-sensitized solar cells. In this case, a binary mixture (75:25) of propylene carbonate (PC) : 3-methoxypropionitrile (MPN), containing 0.015M I₂ plus 0.285M LiI was employed as electrolyte for filling the photo-cells.

On one hand, our experimental results demonstrated that both cathodic systems, ITO/C and ITO/PtO_x, had a very comparable electron transfer kinetics when studied the cathodic semi-reaction I₃^- + 2e^­- --> 3I^- at these electrode surfaces.

Table 1. Electron transfer constants (k°) and cathodic transfer coefficients (∝_c) obtained for the semi-reaction I₃^- + 2e^­- --> 3I^- at ITO/C and ITO/PtO_x cathodes. Electrolyte: 0.015M I₂ plus 0.285M LiI contained in a binary mixture 75:25 of PC:MPN at 25°C. A polycrystalline Pt cathode was also employed for comparison purposes.

cathode	Electron transfer kinetic parameters
	k°/10-4 (cm/s) and ∝c
Pt	5.31	0.27
ITO/PtOx	3.35	0.26
ITO/C	2.70	0.23

On the other hand, a detailed revision of Table 2 reveals that the photovoltaic responses of porphyrin-sensitized solar cells containing ITO/C and ITO/PtO_x cathodes were comparable under simulated solar light (AM1.5, 100mW/cm²). These interestingly results confirmed that Toray^TM/TGP-H-060 carbon – modified ITO cathodes are promising to substitute those PtO_x – modified ITO cathodes typically employed for constructing dye-sensitized solar cells.

Table 2. Photovoltaic responses obtained for porphyrin-sensitized solar cells containing ITO/C and ITO/PtO_x cathodes, where: E_oc, j_sc, ff and ξ are open-circuit potential, short-circuit photocurrent, fill-factor and global conversion efficiency, respectively, under simulated solar light (AM1.5, 100mW/cm²).

cathode	Eoc (V)	jsc (mA/cm2)	ff	ξ(%)
ITO/PtOx	-0.30	1.23	0.39	0.17
ITO/C	-0.35	1.18	0.40	0.19

References

U.López-García, O.A.Castellanos, L.A.Godínez, J.Manríquez, “Electrophoretically-Assisted Deposition of Mesoporphyrin IX on Nanoparticulate TiO₂ Films for Constructing Efficient Dye-Sensitized Solar Cells”, Journal of The Electrochemical Society, 158 (2011) F100-F105.