Solution-processed TiO2 blocking layers in printed carbon-based perovskite solar cells

Abstract The perovskite solar cells with carbon back electrode (C-PSCs) are a promising solar technology due to low-cost, easy and eco-friendly fabrication by printing techniques. It promises also higher stability due to the presence of thick hydrophobic carbon electrode. Besides stability, other problems, including a perovskite quality, its infiltration and particularly, the structure and homogeneity of a thin (30 nm) hole blocking layer that plays a crucial role in PSC efficiency. This work is focused on the preparation and optimization of the thin and failure-free compact sol–gel blocking layer and its application in printed C-PSCs with the layer structure: glass/FTO/blocking TiO2/ mesoporous TiO2/scaffold-space ZrO2/carbon with infiltrated perovskite. Sol-gel blocking layers were prepared by spin-coating techniques from the TiO2 precursors such as TiAcAc, TTIP, and Ti(BuO)4 and optimized by a small addition of TiCl4. The best efficiency (7.8%) was achieved by cells using the blocking layer prepared by mixing of 0.06 M TiCl4 into TiAcAc precursor. Functional layers of printed C-PSC were characterized by AFM, SEM, UV–Vis spectroscopy and conductivity measurement. Cell efficiency was determined from V-A load characteristics under standard daylight exposition. Some correlations were found between the blocking layer conductivity, nano-roughness, optical band gap and the solar cell efficiency.