Low-Temperature Hole Injection and Hole Trap Distribution in Anthracene

A solid and stable electrode has been developed, able to efficiently inject holes into anthracene crystals down to low temperatures. With such an electrode, dark-current measurements have been performed successfully, which show that the exponential distribution of hole traps does not extend to the valence band. In addition two shallow hole trap levels at energies E1 ≡ 0.53 and E2 ≈ 0.2 eV have been observed. This trap distribution has been found for a series of melt-grown anthracene crystals, prepared from different batches of carefully purified starting material.