Spin-dependent recombination of photoinduced carriers in phthalocyanine/C60 heterojunctions

Spin-dependent recombination of photoinduced carriers in H-2-phthalocyanine(H2Pc)/C-60 heterojunctions is studied by electrically detected electron-spin resonance (EDESR) spectroscopy. The EDESR spectrum of the H2Pc/C-60 consists of two components A and B, the g values of which are 2.0018+/-0.0002 and 2.0010+/-0.0002, respectively. The two components are attributed to exchange-coupled localized electron-hole pairs trapped at different types of recombination centers. Component A has spin-flip satellites due to an interaction between the electron (or hole) spin, and its surrounding nuclear spins of protons:which belong to the H2Pc rings. From the satellite intensity, the distance between the electron (or hole) and the protons is estimated to be 4.33+/-0.25 Angstrom, indicating that the localized pairs for the component A locate close to the H2Pc rings. The spin dynamics of the localized pairs for the component A is studied by a microwave recovery experiment, in which the time dependence of the EDESR signal intensity is measured after turning the resonant microwave on and off. A theoretical model of the spin-dependent recombination of the exchange-coupled election-hole pair is proposed with which the experimental results of the microwave recovery are explained. By theoretical analysis, it is found that R greater than or similar to 1 X 10(6) s(-1) and D + W-si = 6.2 (+/- 0.8) x 10(4) s(-1) for component A at room temperature, where R is the recombination rate of the localized pair in the S-z = 0 triplet sublevel, and D and W-si are the dissociation and the spin-lattice relaxation rates, respectively, of the pairs in the triplet sublevels. The photocurrent 12 that is caused by the dissociation of the localized pairs for component A is about 5% of the total photocurrent. [S0163-1829(99)02403-0].