Current noise spectroscopy on mLPPP based organic light emitting diodes

Noise spectroscopy is presented to be a powerful tool to investigate the current flowing in organic light emitting diodes (oLEDs) with high sensitivity. Measurements can be performed over the whole bias range of interest, from reverse bias up to high values of forward bias voltage. From these measurements one can gain insight into the microscopic conduction processes dominating the device current and obtain valuable information for improved device modeling. In particular it is shown that the low frequency power spectrum of the tested oLEDs has a power law dependence around 1/f 1.3 almost irrespective of device characteristics and of measurement conditions. Additionally, noise spectra are also proposed as a means to sense the initial state and the growth of degradation phenomena in these devices. The onset of degradation is shown to be signaled by current spikes that reflect on a net increase of the white noise component of about three orders of magnitude in the power spectral density, when degradation is just hardly beginning to be visible as dark spots on the emitting surface.