Beyond Fullerene Acceptors: Comparison of Exciton Dissociation at Pc/C60 and Pc/PTCDA Interfaces
Steven W. Robey, Gregory J. Dutton
The development of organic photovoltaic technologies would benefit from the introduction of non-fullerene materials to replace the dominant fullerene acceptors. However, efforts to replace fullerenes with non-fullerene polymers or small molecules have resulted in reduced efficiencies, the cause of which is not clear. Increased efficiency for exciton dissociation at fullerene-donor interfaces, compared to non-fullerene acceptors, is one of several possibilities. To examine this possibility, exciton dissociation at the interface between zinc phthalocyanine (ZnPc) and the acceptor perylene-tetracarboxylic-acid (PTCDA) was investigated using time-resolved two-photon photoemission. The exciton dynamics measured for this interface were compared to previous measurements for phthalocyanine interfaces with the fullerene acceptor, C60. The dynamics of S1 excitons excited by a visible pump pulse in phthalocyanine (Pc) layers near the interface with PTCDA were monitored via photoemission with a time-delayed probe pulse to determine the impact of exciton dissociation on the S1 population near the interface. The results of this comparison revealed that exciton dissociation is comparable for Pc interfaces with both acceptors.