Spectroscopic and Morphological Studies of Metal-Organic and Metal-Free Dyes onto Titania Films for Dye-Sensitized Solar Cells

Gabriella Di Carlo,Roberta G Toro,Anna M Paoletti,Cristina Riccucci,Nicola Angelini,Giovanna Pennesi,Giuseppina Padeletti,Gloria Zanotti,Daniela Caschera,Giuseppe Gigli,Gabriel M Ingo,Luisa De Marco

doi:10.1155/2013/582786

Abstract

We have investigated the spectroscopic behavior of three different sensitizers adsorbed onto titania thin films in order to gain information both on the electron transfer process from dye to titania and on the anchorage of the chromophore onto the semiconductor. We have examined by UV-Vis and fluorescence spectroscopy the widely used ruthenium complexcis-di(thiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) (N719), the more recently developed organic molecular 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), and apush-pullzinc phthalocyanine sensitizer (ZnPc). Three type of titania films with different morphology, characterized by SEM and FT-IR measurement, were considered: a mesoporous transparent film deposited by spin-coating (TiMS), a semiopaque film deposited by doctor-blade from mesoporous titania (TiMS_DB) and a semiopaque film deposited by doctor-blade form commercial P25 titania (P25_DB). The use of TiMS is responsible for the adsorption of a higher amount of dye since the mesoporous structure allows increasing the interfacial area between dye and titania. Moreover, the fluorescence emission peak is weaker when the sensitizers are adsorbed onto TiMS. These findings suggest that mesostructured films could be considered the most promising substrates to realize photoanodes with a fast electron transfer process.

Highlights

Dye-sensitized solar cells (DSSCs) are receiving increasing attention during the last decades since they are considered a viable and cost-effective technology for the conversion of sunlight into electricity [1,2,3]
We have examined by UV-Vis and fluorescence spectroscopy the widely used ruthenium complex cisdi(thiocyanato)bis(2,2󸀠-bipyridyl-4,4󸀠-dicarboxylato)ruthenium(II) (N719), the more recently developed organic molecular 3-(5(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), and a push-pull zinc phthalocyanine sensitizer (ZnPc)
Three type of titania films with different morphology, characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) measurement, were considered: a mesoporous transparent film deposited by spin-coating (TiMS), a semiopaque film deposited by doctor-blade from mesoporous titania (TiMS DB) and a semiopaque film deposited by doctor-blade form commercial P25 titania (P25 DB)

Summary

Introduction

Dye-sensitized solar cells (DSSCs) are receiving increasing attention during the last decades since they are considered a viable and cost-effective technology for the conversion of sunlight into electricity [1,2,3] In these devices, metalorganic or metal-free dyes are chemically adsorbed onto a wide band gap semiconductor oxide [1,2,3,4,5,6,7,8]. It is fundamental to investigate and to optimize the dye-substrate interaction that is involved in the electron transfer process [9] Ruthenium sensitizers, such as cis-di(thiocyanato)bis[2,2󸀠-bipyridyl-4,4󸀠-dicarboxylic acid] ruthenium (II) (N3) or its bistetrabutylammonium (TBA) salt counterpart (N719), in combination with thick titania films (>12–15 mm) have shown solar-to-electric power conversion efficiencies up to 11% [2, 10]. Titania films were characterized by scanning electron microscopy (SEM) and by Fourier transform infrared (FT-IR) spectroscopy, whereas the dyesensitized films were studied by UV-Vis and fluorescence spectroscopy

Preparation of Titania Thin Films

Results and Discussion

Conclusions