Application of Optoadmittance and Cross-Correlation Noise Spectroscopy to White OLEDs*

The recently developed method of optoadmittance spectroscopy applies an alternating voltage across a light emitting device and sweeps its frequency across a specified bandwidth. The current through the device and the light emitted are then concurrently measured and the phase delay and amplitude response are determined. Here, the method is applied to an organic LED (OLED) which emits white light. The OLED is composed of three layers responsible for emission of light composed of three distinct wavelengths. Optoadmittance spectroscopy is performed while using optical bandpass filters to examine only one of these wavelengths at a time. This method is then combined with cross-correlation noise spectroscopy, where the noise present in the optical signal is cross-correlated with the noise present in the electrical current. This is also done while using optical filters to select a specific wavelength range. By comparing the frequency response determined by optoadmittance spectroscopy with the power spectral density of the cross-correlated noise, we characterize relaxation processes related to the three different color components.