Characterization of the Pore Filling of Solid State Dye Sensitized Solar Cells with Photoinduced Absorption Spectroscopy

Carol Olson,Frank Lenzmann,Klaas Bakker,Dirk Veldman

doi:10.1155/2011/513089

Abstract

Near steady-state photoinduced absorption (PIA) and UV-Vis absorption spectroscopy are used to characterize the pore filling of spiro-MeOTAD (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)9,9′-spirobifluorene) into the nanoparticulate TiO2electrode of a solid-state dye-sensitized solar cell (ssDSC). The volumetric ratio of filled to unfilled pore volumes, as well as the optical signature of interacting chemical species, that is, the hole-transfer yield (HTY), are investigated. PIA spectroscopy is used to measure the HTY, relative to the amount of spiro-MeOTAD present, without needing to determine the extinction coefficients of the dye and spiro-MeOTAD cation species. The Beer-Lambert law is used to relate the relative PIA signal to the penetration length of the hole-conductor in the TiO2film. For the sample thickness range of1.4–5 μm investigated here, the optimum characteristic penetration length is determined to be3.1+0.46 μm, which is compared to 1.4 μm for the 200 mgmL−1concentration of spiro-MeOTAD conventionally used. Therefore, doubling the effective penetration of spiro-MeOTAD is necessary to functionalize all the dye molecules in a ssDSC.

Highlights

First generation dye sensitized solar cells (DSCs) are composed of a high surface area nanoparticulate TiO2 electrode, onto which a ruthenium dye, such as the Z907 dye (cis-RuLL (SCN)2 (L = 4,4 -dicarboxylic acid2,2 -bipyridine, L = 4,4 -dinonyl-2,2 -bipyridine), [1, 2] is adsorbed, immersed in a liquid electrolyte, typically containing an I−/I−3 redox couple, which conducts holes to a platinum counter electrode [3]
We propose a method of using photoinduced absorption spectroscopy (PIA) to relatively determine the dye regeneration yield of an sensitized solar cell (ssDSC), and we show its relationship to the filling fraction
Because the effects of viscosity were observed in the thicknesses of the spiro MeOTAD films spun on flat substrates, a correction factor was proposed for the filling fraction to account for the effects of viscosity in capillary infiltration

Summary

Introduction

TAS has been used to observe the kinetics of various electron transfer processes in the DSC [12,13,14] and to compare the HTY of various hole-conducting materials to spiro-MeOTAD [15]. Snaith et al [18] proposed that the amount of spiroMeOTAD in the pores of the TiO2 is equal to the concentration of spiro-MeOTAD of the starting solution, c, plus an amount from the wet overlayer, resulting from the spincoating, which is driven into the film by a concentration gradient setup during the process of evaporation. We demonstrate that a single PIA measurement of a ssDSC at two different wavelengths can be used as a relative measure for the dye regeneration yield

Experimental

Results and Discussion

Photoinduced Absorption Spectroscopy

Conclusions