Enhancing the Open-Circuit Voltage of Molecular Photovoltaics Using Oxidized Au Nanocrystals

For organic photovoltaics (OPV) to realize applications effective strategies to maximize the open-circuit voltage must be developed. Herein we show that solution-processed surface-oxidized Au nanoctystals (o-AuNC) dramatically increase the open-circuit voltage (V-oc) of OPV cells based on boron-subphthalocyanine chloride (SubPc)/C-60 and chloro-aluminum phthalocyanine (CIAIPc)/C-60 heterojunctions when incorporated at the interface between the hole-extracting electrode and the phthalocyanine donor layer. In addition, the cell-to-cell variation in V-oc is reduced by up to 10-fold combined with a large reduction in the light intensity dependence of V-oc, both of which are important advantages for practical application. The largest increase in V-oc is achieved for SubPc/C-60-based cells which exhibit a 45% increase to 1.09 +/- 0.01 V-an exceptionally high value for a single junction small molecule OPV. Remarkably these improvements are achieved using submonolayers of o-AuNC, which can be rationalized in terms of the exceptionally high work function of o-AuNC (similar to 5.9 eV) and geometric electric field enhancement effects.