Spin-dependent recombination of photoinduced carriers in H 2 -phthalocyanine (H 2 Pc͒/C 60 heterojunctions is studied by electrically detected electron-spin resonance ͑EDESR͒ spectroscopy. The EDESR spectrum of the H 2 Pc/C 60 consists of two components A and B, the g values of which are 2.0018Ϯ0.0002 and 2.0010Ϯ0.0002, 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 hole͒ spin, and its surrounding nuclear spins of protons which belong to the H 2 Pc rings. From the satellite intensity, the distance between the electron ͑or hole͒ and the protons is estimated to be 4.33Ϯ0.25 Å, indicating that the localized pairs for the component A locate close to the H 2 Pc 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 electron-hole pair is proposed with which the experimental results of the microwave recovery are explained. By a theoretical analysis, it is found that Rտ1ϫ10 6 s Ϫ1 and DϩW sl ϭ6.2 (Ϯ0.8)ϫ10 4 s Ϫ1 for component A at room temperature, where R is the recombination rate of the localized pair in the S z ϭ0 triplet sublevel, and D and W sl are the dissociation and the spin-lattice relaxation rates, respectively, of the pairs in the triplet sublevels. The photocurrent I 2 that is caused by the dissociation of the localized pairs for component A is about 5% of the total photocurrent.

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