56.3: Study of Space Charges in Hole Transfer Layer of OLED Devices using Impedance Spectroscopy and Transient Electroluminescence

The charge generation and transportation phenomena of OLED devices based on the different hole-transfer materials, HTL1 and HTL2, have been investigated employing Impedance Spectroscopy (IS) and Transient Electroluminescence (TEL). The capacitance resulted from the quantity of space charges in HTL1 and HTL2 have been observed to be distinguishable by means of both the Capacitance-Voltage and Frequency-dependent Capacitance measurements. The capacitance increment by the space charges is also seen in the extracted RC components of the equivalent circuit, which is determined from the comparison between the quantitatively calculated and the experimentally observed data in Cole-Cole plot. The increased space charges of HTL2 are found to enhance the hole mobility across hole transfer layer which was derived from the delayed response time of Transient EL.