Zr-Nanoxide ZT/DC Slot-die coating formulation for the deposition of zirconia insulating layers in monolithic Perovskite Solar Cells. Zr-Nanoxide ZT/DC is a slot-die coating formulation for the deposition of insulating mesoscopic zirconium dioxide layers in monolithic Perovskite Solar Cells. Slot-die coating at 0.5 m/min, 0.2 mL/min typically yields a 500 nm thick layer after firing at 500°C for 45 min. The oxide particles form a mesoporous coating allowing for perovskite impregnation of the underneath layers. Thanks to a composition exclusively made of nanoparticles, the resulting zirconia layers can be extremely thin, down to the micron, whilst ensuring electrical insulation without sacrificing device thinness and charge extraction. Zr-Nanoxide ZT/DC is best used in conjunction with Ti-Nanoxide BL150/DC for the compact titania layer, Ti-Nanoxide T165/DC for the mesoporous titania layer, and Elcocarb B/DC for the carbon layer.