Electron–Hole Pairs Generated in the Crystalline Phase of Polymer Diodes Studied by Electrically Detected Magnetic Resonance Techniques

Abstract

The properties of electron–hole (e–h) pairs generated in a working poly(3-hexylthiophene) (P3HT) diode are investigated by electrically detected magnetic resonance (EDMR) techniques. The EDMR intensity is shown to increase with increasing density of injected electrons for a given hole density, demonstrating that the EDMR signal arises from an e–h pair. The EDMR spectrum consists of two Gaussian curves, one of which gives a g-value very similar to that of hole carriers, suggesting that the EDMR spectrum is given by the sum of electron spin resonance (ESR) spectra from hole and electron carriers forming e–h pairs. Bias-dependent correlation between carriers and e–h pairs under diode operation is examined directly from independent measurements of near-infrared (NIR) spectroscopy for carriers and EDMR for e–h pairs. When the bias is increased to above a threshold, the EDMR signal is strongly reduced despite a gradual increase in the NIR signals, providing evidence that the e–h pairs are dissociated by an elec...