Department of Physics
Condensed Matter Seminar

Numerous studies of spin-dependent recombination and spin relaxation of charged excitations in π-conjugated polymers have been conducted in recent years due to the surge of application research in organic light emitting diode, organic photovoltaic devices and organic spin-valve devices. Controversial models regarding the recombination dynamics and spin dynamics were brought up from research groups based on different experimental methods. By studying continuous wave and transient spectroscopy of optically detected magnetic resonance (ODMR), which stems from spin sublevels response to double excitation of both laser illumination (or carrier injection), and microwave radiation under spin resonance conditions, and therefore is sensitive to both excess-carrier recombination rate, γ and spin relaxation rate γ_SL, we promoted this non-geminate polaron-pair recombination model to achieve fundamental understanding of spin dynamics of charged excitations in π-conjugated polymers. Specifically we show that the in-phase (I) ODMR component reverses sign at a frequency ƒ₀ beyond which it decays off, and that ƒ₀ depends on γ, γ_SL, and the microwave power, Ρ_MW; and thus a thorough analysis yields all of the important rate values involved. We also demonstrate our method in analyzing spin dynamics of photo-excited polarons in films of pristine MEH-PPV, a poly (phenylene vinylene) derivative, as well as MEH-PPV doped with various concentrations of radical impurities.