Nanoscale geometric electric field enhancement in organic photovoltaics.

Generic design rules for electrode-organic semiconductor contacts that transcend specific materials are urgently required to guide the development of new electrodes and provide a framework for engineering this important class of interface. Herein a novel nanostructured window electrode is utilized in conjunction with three-dimensional electrostatic modeling to elucidate the importance of geometric electric field enhancement effects at the electrode interfaces in organic photovoltaics. The results of this study show that nanoscale protrusions at the electrode surfaces in organic photovoltaics dramatically improve the efficiency of photogenerated charge carrier extraction to the external circuit and that the origin of this improvement is the local amplification of the electrostatic field in the vicinity of said protrusions. This wholly geometric approach to engineering electrodes at the nanoscale is materials generic and can be employed to enhance the efficiency of charge carrier injection or extraction in a wide range of organic electronic devices.

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.

Direct versus indirect H atom elimination from photoexcited phenol molecules.

The active role of the optically dark pi sigma* state, following UV absorption, has been implicated in the photochemistry of a number of biomolecules. This work focuses on the role of the pi sigma* state in the photochemistry of phenol upon excitation at 200 nm. By probing the neutral hydrogen following UV excitation, we show that hydrogen elimination along the dissociative pi sigma* potential energy surface occurs within 103 +/- 30 fs, indicating efficient coupling at the S1/S2 and S0/S2 conical intersections, with no identifiable role of statistical unimolecular decay of vibronically excited (S0) phenol in the timeframe of our measurements.