A comprehensive electron paramagnetic resonance study of influence of annealing on defect center in phosphorus ion-implanted C60 films

Electron paramagnetic resonance (EPR) measurements have been performed to investigate the effect of annealing on paramagnetic defect center in P+-implanted C60 films, in order to control and improve the electronic properties of the implanted films towards photovoltaic applications. We have found a reduction in the dangling bond density upon annealing by approximately a one order of magnitude, in the temperature range between 100°C and 700°C, regardless of the annealing media whether vacuum or forming gas (N2/H2). The reduction in spin defect density was ascribed to the decrease in disordered dangling bond as a consequence of the reconstruction of the less stable defect sites. Indeed the modification in the spin density is accompanied with an improvement in the electrical conductivity and band structure of the films. Also, in the annealed carbon films, a correlation was observed among linewidth, relaxation times, and optical gap. In addition, we report about the temperature dependence of the linewidth, signal intensity and the susceptibility of annealed films. The susceptibility follows the Curie-law at sufficiently low temperature, while above 180 K a deviation was observed. The prime novelty of this study is that it is the first EPR study of effects of annealing on defect center in P+- implanted C60 films.