Solution processable transition metal oxide ultra-thin films as alternative electron transport and hole blocking layers in dye sensitized solar cells

Abstract

An electron transporting and hole-blocking layer (ETL) between the fluorine-doped tin oxide (FTO) and mesoporous titanium dioxide interface of photoanode is essential in dye-sensitized solar cells (DSCs) for improving their photovoltaic performance. In the present work, we have examined the potential for further improving device performance by using alternative materials for ETLs. Accordingly, the effect of replacing TiO2 based ETLs with spin coated ultra-thin transition metal oxides (TMOs), molybdenum trioxide (MoO3) and tungsten trioxide (WO3) films has been studied. TMO films of 10 nm thickness have been found to be optimal for obtaining good transparency and charge transport properties, without compromising device performance. Further, devices fabricated with surfactant assisted (SA-) MoO3 ETLs have shown efficiency ∼4%, which is comparable with devices based on conventionally prepared TiO2 ETLs. In addition, a significant improvement in efficiency (15 %) has been observed for DSCs prepared using SA-WO3 films. The overall improvement in device efficiency is attributed to the increase in short-circuit current density without loss of open circuit potential and fill factor. Detailed analyses of results suggest that in addition to surface morphology, transparency and charge transport properties; oxygen vacancies in sub-stoichiometric TMOs also plays an important role in determining the device performance. The findings reveal that TMOs have significant potential to replace TiO2 ETL in DSCs and other third generation solar cell, viz. perovskite and polymer solar cells.