S inglet oxygen is a common reactive oxygen species that is formed as a byproduct of many photosensitized processes. Due to its high reactivity, singlet oxygen irreversibly damages a range of unsaturated organic compounds. 1À4 The 1 Δ g r 3 Σ g

Direct observation of triplet energy transfer from sensitiser to emitter is modelled and provides comprehensive description of bimolecular upconversion.

For high band gap solar cells, organic molecule based upconverter materials are promising to reduce transmission losses of photons with energies below the absorption threshold. We investigate the approach of embedding the organic upconverter DPA:PtOEP directly into each second layer of a Bragg stack to achieve an enhancement of upconversion performance. The two major effects that influence the upconversion process within the Bragg stack are simulated based on experimentally determined input parameters. The locally increased irradiance is simulated using the scattering matrix method. The variation of the density of photon states is obtained from calculations of the eigenmodes of the photonic crystal using the plane wave expansion method. A relative irradiance enhancement of 3.23 has been found for a Bragg stack of 31 layers including λ/8-layers on both sides. For suppressing the loss mechanism of direct sensitizer triplet decay via variations of the density of photon states, a different design of the Bragg stack is necessary than for maximum irradiance enhancement. In order to find the optimum design to increase upconversion quantum yield, both simulation results need to be coupled in a rate-equation model. The irradiance enhancement found in our simulation is significantly higher than the one found in the simulation of a grating-waveguide structure, which achieved an increase of upconversion quantum yield by a factor of 1.8. Thus, the Bragg structure is very promising for upconversion quantum yield enhancement

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Upconversion is a promising technique for significantly enhancing the efficiency of photovoltaic cells. Molecular systems provide an environment in which long lived triplet states can be exploited to achieve high upconversion efficiencies under solar illumination. We report on the investigation of bi-molecular triplet-triplet annihilation upconversion (TTA-UC) in a Palladium (II) tetrakisquinoxalino porphyrin (PQ4Pd)/rubrene solution. These molecules were studied in solution using UV/VIS spectroscopy to determine their stability in air over a period of weeks. Transient absorption spectroscopy (TAS) was used to directly measure the lifetime of triplet states within these mixtures and hence determine the photoinduced kinetics of the system. The lifetime of porphyrin triplets was reduced from 92.4 µs in pristine PQ4Pd to 2.4 µs in the presence of rubrene. From this change, the rate constant associated with triplet energy transfer (݇ ்ா் ) was calculated as 3. 38 ൈ 10 ଼ ‫ܯ‬ ିଵ ‫ݏ‬ ିଵ . Additionally, a reduction in the absorption of 530 nm light (the ground state rubrene absorption peak) was observed, while the mixture was pumped at the absorption peak of the porphyrin (670 nm). This change became apparent nearly 6 µs after the laser pulse, showing energy transfer from the porphyrin to the rubrene, and allowing further insight into the kinetics of the mechanism.