After rinsing the sensitized electrodes with ethanol and allowing them to dry, a chlorobenzene solution containing 150 mM SPIRO-OMeTAD, 200 mM 4-tert-butylpyridine and 20 mM LiTFSI was applied to create the HTM film. This was achieved by allowing 80 µL of the solution to permeate the sensitized electrode for 30 s and then spin-coating for 30 s at 2000 rpm.