Photochemical Upconversion Enhanced Solar Cells: Effect of a Back Reflector

Abstract

Photochemical upconversion is applied to a hydrogenated amorphous silicon solar cell in the presence of a back-scattering layer. A custom-synthesized porphyrin was utilized as the sensitizer species, with rubrene as the emitter. Under a bias of 24 suns, a peak external quantum efficiency (EQE) enhancement of ∼ 2% was observed at a wavelength of 720 nm. Without the scattering layer, the EQE enhancement was half this value, indicating that the effect of the back-scatterer is to double the efficacy of the upconverting device. The results represent a figure of merit of 3.5 × 10 −4 mA cm −2 sun −2 , which is the highest reported to date.

Photochemical upconversion: present status and prospects for its application to solar energy conversion

“…With this topology inside a standard 1 cm diameter cuvette we realized a twofold increase of the UC-related current increase as compared to the quasi-infinite case. 93 The comparison to the optical modeling results 47,104 shows that the configuration is not optimal, but reasonably close to the optimum situation. At the same time it allows for facile freeze-pump-thaw deaeration which led us to adapt this configuration to be the standard experimental setup.…”

“…102,103 In order to minimize parasitic absorption, the overlap between the emission band of the TTA emitter and the absorption bands of both emitter and sensitizer must be minimized. Figure 5 shows the situation for two TTA solutions employed in our studies, 47,93,95 plotted for typical concentrations. It can be seen that there are slight overlaps between the rubrene emission and its own absorption band (self-absorption) as well as with the porphyrin sensitizer Q-and Soret bands.…”

“…93 The effect of the resulting textured surface was to multi-pass the incoming light to improve absorption, while also improving the out-coupling of upconverted light. Indeed, with a close-packed structure of 100 µm spheres, most of the surface area presents an optical depth less than this value.…”

“…91 For a useful review on upconversion nanophosphors for solar cell applications, see the recent review of Ramasamy et al 92 In 2012, our group demonstrated the first solar cell assisted by triplet-triplet annihilation upconversion, using the example of an amorphous silicon thin-film solar cell. 47,93,94 The approach was successively applied to organic solar cells 95 as well as dye-sensitized solar cells. 96 Details about these results and a comparison to the lanthanoid upconversion system are given below.…”

BIOPHYSCHEM2011: A Joint Meeting of the Australian Society for Biophysics and the RACI Physical Chemistry Division

“…Tim Schmidt (U. Sydney) and co-workers report studies incorporating triplet-triplet annihilation photon up-conversion in a solar cell equipped with a back-scattering layer. [4] With this strategy, longer-wavelength photons are converted to shorter wavelengths, exploiting the triplet-state interactions of sensitizer molecules (porphyrins) and emitter molecules (rubrenes). With the additional aid of a backscattering layer, higher quantum efficiencies for the device are reported for long-wavelength photons that would otherwise be wasted in a conventional solarcell device.…”