Transient photovoltage and photoluminescence study of exciton dissociation at indium tin oxide/pentacene interface

The exciton dissociation at ITO/pentacene interface is studied by means of transient photovoltage measurement. Opposite to ITO/NPB, ITO/CuPc or ITO/C60 interface where polarity change of transient photovoltage is observed, no interfacial dissociation is found at room temperature, which indicates a lack of Frenkel excitons in pentacene. Temperature-dependent photoluminescence (PL) is investigated. More like the behavior of inorganic semiconductors, the integrated PL intensity exhibits monotonic decrease with increasing temperature. A nonradiative path with characteristic activation energy of 8 meV is found to dominate at room temperature. The PL measurement also indicates that like in inorganic semiconductors, other types of excitation, for example, free carriers, could be responsible for the photoelectric processes.