Distance-Dependent Ultrafast Dynamics at H2Pc\C60 Interfaces
Gregory J. Dutton, Steven W. Robey
We investigated the distance-dependence of interfacial charge transfer processes at the donor-acceptor heterojunction formed between H2Pc and C60. The interface region was formed layer-by-layer using organic molecular beam epitaxy (MBE). For each thickness H2PC S1 excitons were created with a 1.55 eV pump pulse and the subsequent dynamics of the exciton population, including intraband relaxation and donor-acceptor charge transfer, were followed by time-resolved photoemission using a delayed UV probe pulse. A charge transfer rate of (2.3 ± 0.3) x 1012 s-1 was measured for the layer of H2Pc immediately adjacent to C60 but no evidence of significant charge transfer was detectable for H2Pc layers beyond the first. The impact of the structure of this interface determined using scanning tunneling microscopy is considered.