Transparent conducting oxides and their performance as substrates for counter electrodes of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are constructed on top of transparent conducting oxide (TCO) substrates that permit incident light to enter the cells and facilitate charge transport from back contact to the external circuit. The most common TCO substrate used in DSSCs, as well as other optoelectronic devices, is an F-doped tin oxide (FTO). Another tin oxide-based TCO is Indium tin oxide (ITO), which is also used in optoelectronic devices. However, zinc oxide-based TCOs –aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO) – were not used that much, especially in DSSCs. In the present work, we examined the suitability of four transparent conducting oxides – FTO, ITO, AZO, and GZO – for the application in DSSCs as substrate. We employed all four TCOs to fabricate platinized counter electrode (CE) for DSSCs in three different methods: thermal reduction of Pt precursor at 380 °C, chemical reduction of Pt precursor at 70 °C, and RF-sputtering Pt at room temperature. The cation-doped zinc oxide-based TCOs are not thermally and chemically stable. However, FTO, being anionic-doped tin oxide-based TCO, is the most thermally and chemically stable among the four TCOs studied in this work.