Study of the oxidation and reduction behavior of organic materials using cyclic voltammetry

The accurate evaluation of energy levels is essential for optimizing the performance of organic light-emitting diode (OLED) materials. In this study, we systematically analyzed the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of small organic molecules widely used in various layers of OLED devices using cyclic voltammetry (CV). These molecules include the thermally activated delayed fluorescence (TADF) emitters 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and 4,5-bis(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN). To maximize measurement reliability, we conducted optimization studies across various environmental parameters, such as sweep direction, scan rate, material concentration, solvent, and working electrode type. As a result, we established analytical conditions that ensured a stable potential window tailored to the characteristics of the solvent and electrode, while minimizing background current interference. In particular, we successfully performed negative CV scans, which had previously been challenging to measure reliably due to various technical difficulties. This is significant, as it provides an effective and practical method for the independent and intuitive evaluation of the LUMO levels of organic materials solely through optimized electrochemical CV analysis.