Electron spin resonance studies on defects in phosphorus ion-implanted C60 films

Paramagnetic defects produced by phosphorus ion implantation of C60 films and the influence of annealing on dangling bonds defect center have been studied by electron spin resonance (ESR) to improve the properties of P+-implanted C60 films for solar cell applications. The films implanted at room temperature reveal the presence of a paramagnetic defect center, which originated from the carbon dangling bonds, with g=2.0036±0.0004. The volume concentration of the defect center increases with the implantation dose, from approximately 4.5×1021 to 4.6×1022 cm−3 for the lowest implantation dose of 1×1013P+ ions cm−2 and the highest implantation dose of 5×1015 P+ ions cm−2, respectively. The increase in dose also causes a narrowing of the line width (from 2.6 to 2.15 G) although the g-value of the single Lorentzian line remains unchanged. The narrowing is attributed to exchange (motional) interaction. The ESR results imply that no significant graphitization has occurred as a result of implantation. Furthermore, upon annealing at a temperature of 773 K the spin defect density is reduced by a factor of 3.5, while the g-value remains centered at the same magnetic field. This reduction is due to a reconstruction of the less stable spin defect sites. The originality of this paper is that it is the first ESR study of defects produced by phosphorus implantation of C60 films.