An experimental study on the molecular organization and exciton diffusion in a bilayer of a porphyrin and poly(3-hexylthiophene)

The exciton root-mean-square displacement (?D) in regioregular poly(3-hexylthiophene) (P3HT) deposited onto meso-tetrakis (n-methyl-4-pyridyl) porphyrin tetrachloride (H2TMPyP) has been determined from the photovoltaic response of a device based on these materials in a bilayer configuration. Excitons formed on illumination that reach the interface between H2TMPyP and P3HT can undergo interfacial charge separation by electron injection into the H2TMPyP and hole injection into the P3HT. The incident photon to current efficiency (IPCE) exceeds 20% over a broad wavelength regime. The theoretical analysis of the IPCE values gives a value for ?D in H2TMPyP that amounts to 14 nm, while for P3HT a value of 18 nm is obtained. The latter value exceeds literature values reported for P3HT by almost a factor of 3. X-ray diffraction analysis shows that in the studied bilayer the P3HT backbones are aligned parallel to the interface with H2TMPyP. In contrast, in the case of P3HT deposited onto TiO2, for which ?D has been reported to equal only 7 nm, hardly any organization of the P3HT backbones is observed. The excitonic coupling between P3HT backbones deposited onto H2TMPyP is as high as 125?cm?1, a factor of 3 larger than the excitonic coupling between the disordered P3HT backbones that amounts to 47?cm?1. The difference illustrates the importance of controlling the molecular organization for the realization of efficient energy transfer in organic optoelectronics.DelftChemTechApplied Science

Silver Nanocubes Coated in Ceria: Core/Shell Size Effects on Light-Induced Charge Transfer

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO2 nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT. A 4-mercaptobenzoic acid (4-MBA) linker between core and shell acts as a Raman probe for CT. For all Ag@CeO2 nanocubes, CT increases with decreasing excitation wavelength, with notable increase at and below 514 nm. This is fully explainable by CT from silver to the 4-MBA LUMO, with the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO gap of 2.28 eV (543 nm). A second general trend observed is an increase in CT yield with ceria shell thickness, which is assigned to relaxation of the excited electron further into the ceria conduction band, potentially producing defects