Spin-dependent recombination of photoinduced carriers in phthalocyanine/C-60 heterojunctions

Spin-dependent recombination of photoinduced carriers in H-2-phthalocyanine (H2Pc)/C-60 heterojunctions is studied by electrically detected electron-sp in resonance (EDESR) spectroscopy. The EDESR spectrum of the H2Pc/C-60 cons ists of two components A and B, the g values of which are 2.0018+/-0.0002 a nd 2.0010+/-0.0002, respectively. The two components are attributed to exch ange-coupled localized electron-hole pairs trapped at different types of re combination centers. Component A has spin-flip satellites due to an interac tion between the electron (or hole) spin, and its surrounding nuclear spins of protons:which belong to the H2Pc rings. From the satellite intensity, t he 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 compon ent A locate close to the H2Pc rings. The spin dynamics of the localized pa irs for the component A is studied by a microwave recovery experiment, in w hich the time dependence of the EDESR signal intensity is measured after tu rning the resonant microwave on and off. A theoretical model of the spin-de pendent recombination of the exchange-coupled election-hole pair is propose d with which the experimental results of the microwave recovery are explain ed. 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 pai r 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 triple t sublevels. The photocurrent 12 that is caused by the dissociation of the localized pairs for component A is about 5% of the total photocurrent. [S01 63-1829(99)02403-0].