Optimized TiO2 blocking layers for dye-sensitized solar cells (DSSC)

Abstract

In recent years much attention has been paid to dye-sensitized solar cells due to their low cost and wide applicability. The modest efficiencies achieved by these devices are caused by several phenomena including electronic losses due to parasitic electronic reactions. One of the most common way to reduce the electronic losses is to introduce a compact layer of conductive material (blocking layer) between the transparent conductive substrate and the sensitized semiconductor film. Aim of this work was to asses the correlation between the most common deposition processes and the final properties of the blocking layers produced by them. The blocking layer of TiO2 was prepared on FTO glass using two of the most commonly used colloidal deposition processes: dip and spin coating. The results obtained with the conventional dip coating were compared with the ones coming from spin coating of two different solutions of TiCl4 (50 mM). These solutions were characterized in terms of viscosity, surface tension and contact angle. The spin coating parameters were optimized on the basis of these analysis. The influence of subsequent cycles of deposition (2,4,6) was also evaluated. The TiO2 films obtained were deeply characterized (AFM, SEM, UV-vis and electrochemical measurement) in order to assess the best conditions needed to obtain an efficient blocking layer (BL)