Dye sensitized solar cells (DSCs) are considered promising low-cost and environmental-friendly devices for solar energy conversion. These cells are based on a nanocrystalline TiO2 mesoporous film functioning as photoanode, that therefore collects and transports the photo-generate electrons. One of the major advantages of the DSC technology is the possibility of producing the TiO2 photoanode with low cost and easy scalable processes; among them screen-printing is the most favorable one due to its high reproducibility, easy scalability and extreme flexibility. One of the most critical factors of this process is the composition of the screen-printing ink, generally consisting of a complex combination of a ceramic powder, a solvent, a binder and a dispersant. Firstly reported by Ito et alt. , the formulation including P25 TiO2 nanopowders, terpineol, ethyl cellulose as binder, water and acetic acid as dispersant is widely accepted as a reference for inks to be used for the production of DSCs, due to the positive results demonstrated. However, despite the huge amount studies involving this system, there is still only a very limited knowledge about the effective role of water and its impact on the different phases of the process. The objective of this study was therefore the comprehensive investigation of the effect water in a terpineol based TiO2 screen-printing ink, aimed to a deep understanding of its real contribute along all the phases of the production of a DSC photoanode. For this scope, TiO2 inks with different amounts of water were realized. The effects of water on the inks were analyzed considering the particle dispersion (DLS) and rheological behavior, whereas the deposited layers were analyzed in terms of morphology (FE-SEM), roughness (profilometry) transmittance (UV-Vis spectroscopy) and dye adsorption capability. Finally, the observed properties were correlated to the performances and the electrochemical behavior (EIS) of complete DSCs. These characterizations allowed the identification of a strong effect of water in increasing the dispersion and the time stability of the particle suspensions, leading to an improved flow behavior of the inks due to a lower amount of particle aggregates. As a consequence, the ceramic layers derived from the water-modified samples exhibited an improved morphology compared to the one of the reference system without water. This produced an enhancement of the optical properties and the dye loading, both fundamental parameters for the performance of the final cell. Finally, the testing of the complete devices pointed out significant improvements for the water modified systems. In particular the sample with the highest amount of water resulted the best-performing, recording an increase in efficiency of about the 10% compared to the reference device.
Understanding the effect of water in the formulation of TiO2 screen-printing inks for Dye-sensitized Solar Cells
Riccardo Bendoni;Nicola Sangiorgi;Alex Sangiorgi;Alessandra Sanson
2015
Abstract
Dye sensitized solar cells (DSCs) are considered promising low-cost and environmental-friendly devices for solar energy conversion. These cells are based on a nanocrystalline TiO2 mesoporous film functioning as photoanode, that therefore collects and transports the photo-generate electrons. One of the major advantages of the DSC technology is the possibility of producing the TiO2 photoanode with low cost and easy scalable processes; among them screen-printing is the most favorable one due to its high reproducibility, easy scalability and extreme flexibility. One of the most critical factors of this process is the composition of the screen-printing ink, generally consisting of a complex combination of a ceramic powder, a solvent, a binder and a dispersant. Firstly reported by Ito et alt. , the formulation including P25 TiO2 nanopowders, terpineol, ethyl cellulose as binder, water and acetic acid as dispersant is widely accepted as a reference for inks to be used for the production of DSCs, due to the positive results demonstrated. However, despite the huge amount studies involving this system, there is still only a very limited knowledge about the effective role of water and its impact on the different phases of the process. The objective of this study was therefore the comprehensive investigation of the effect water in a terpineol based TiO2 screen-printing ink, aimed to a deep understanding of its real contribute along all the phases of the production of a DSC photoanode. For this scope, TiO2 inks with different amounts of water were realized. The effects of water on the inks were analyzed considering the particle dispersion (DLS) and rheological behavior, whereas the deposited layers were analyzed in terms of morphology (FE-SEM), roughness (profilometry) transmittance (UV-Vis spectroscopy) and dye adsorption capability. Finally, the observed properties were correlated to the performances and the electrochemical behavior (EIS) of complete DSCs. These characterizations allowed the identification of a strong effect of water in increasing the dispersion and the time stability of the particle suspensions, leading to an improved flow behavior of the inks due to a lower amount of particle aggregates. As a consequence, the ceramic layers derived from the water-modified samples exhibited an improved morphology compared to the one of the reference system without water. This produced an enhancement of the optical properties and the dye loading, both fundamental parameters for the performance of the final cell. Finally, the testing of the complete devices pointed out significant improvements for the water modified systems. In particular the sample with the highest amount of water resulted the best-performing, recording an increase in efficiency of about the 10% compared to the reference device.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
