Photoinduced charge carriers in conjugated polymer-fullerene composites studied with light-induced electron-spin resonance

Detailed studies on photoinduced spins in conjugated polymer/fullerene comp osites using (cw) light-induced electron-spin-resonance (LESR) technique ar e reported. Two overlapping LESR lines are observed, from positive polarons on the polymer chains and negative charges on the fullerene moieties. Micr owave power saturation studies show different relaxation times for these tw o spins, ruling out spin-exchange correlations, giving clear evidence of in dependent spins. The unusually high relaxation rate of the fullerene monoan ionic spins is of intrinsic origin, and discussed in terms of a splitting o f the T-1u level by a Jahn-Teller-type distortion as proposed in the litera ture. Further, we observed two distinct contributions to LESR signals: a pr ompt one and a persistent one. The excitation light intensity dependence of the prompt contributions into the P+ and C-60(-) ESR signals is of bimolec ular type (I-0.5), and implies mutual annihilation within the created (P+ . .. C-60(-)) pair. The persistent contribution is found to be excitation int ensity independent, and is proposed to originate from deep traps due to dis order. [S0163-1829(99)0112-X].