Optimization of the ETL titanium dioxide layer for inorganic perovskite solar cells

Abstract

Titanium dioxide layers are the most popular electron transport layer (ETL) in perovskite solar cells. However most studies focuses on mesoporous structure and application with organic–inorganic hybrid perovskite. In this study, the topic of ETL in planar structure of inorganic CsPbBr₃ perovskite solar cells was tackled, the presented approach will reduce production costs and improve cell stability, which is the greatest drawback of perovskite cells especially organic–inorganic perovskite. The potential application of these technology are greenhouses and building integrated PV sector. Here, the two TiO₂ precursors titanium(IV) ethoxide in ethanol and titanium(IV) bis(acetylacetonate) diisopropoxide (Tiacac) were investigated, optimized and compared. TiO₂ layers were deposited on high roughness FTO, without the use of a mesoporous layer, by spin coating method. The correlation between stock solution concentration and thickness of manufactured layers was tracked for both precursors as well as their difference in morphology of the final films and other properties. In particular, conformality and optical properties are better for Tiacac. Slightly lower refractive index of Tiacac-based titania reduced the reflective losses from 7.3 to 6.9% effectively. The obtained layers were used for inorganic solar cells of CsPbBr₃ perovskite to finally settle the issue of optimal thickness and precursor. It is interesting that despite the supremacy in investigated properties of commonly used of the precursor Tiacac, the results of the cells pointed to the Tieth. The efficiency of the champion cell is 6.08% for Tieth, while 5.62% is noted for Tiacac. Trying to figure out this riddle, we shed a new light on the phenomena going on the ETL/inorganic perovskite interface investigating nanoroughness.