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 nanocrystals (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 (ClAlPc)/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 (∼5.9 eV) and geometric electric field enhancement effects.