A high performance liquid chromatography method to determine phenanthroline derivatives used in OLEDs and OSCs

A high performance liquid chromatography (HPLC) method to detect commonly used electron transport layer (ETL) and hole blocking layer (HBL) materials in organic light emitting diodes (OLED) and organic solar cells (OSC) was established and optimized. The novel method enables the investigation of degradation processes of a range of ETL and HBL materials that were previously difficult to discriminate using the HPLC technique. For instance, 4,7-diphenyl-1,10-phenanthroline (Bphen) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), which are commonly used in OLEDs and OSCs, as well as the new phenanthroline derivatives 2,4,7,9-tetraphenyl-1,10-phenanthroline (TPphen), (2–naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (HNBphen) and 2,9-di(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (NBphen) were distinguished. The detection of these molecules was achieved on a phenyl column using an acetonitrile/water mixture (78:22, v/v%) as mobile phase and a photodiode array detector (PDA) for absorbance detection. The factors affecting peak tailing were studied and optimized. The addition of triethylamine (TEA) to the mobile phase after flushing the HPLC system with ethylenediaminetetraacetic acid disodium salt (Na2EDTA) showed the best reduction of the tailing effect. Furthermore, the influence of the tailing on the calculation of the peak area from HPLC chromatograms was investigated.