NON-COHERENTLY EXCITED PHOTON UPCONVERSION: SUN-SPECTRUM ENGINEERING AND SOLAR CELLS
T. Miteva, G. Nelles
Sony Deutschland GmbH, Materials Science Laboratory, Hedelfingerstr. 61, 70327 Stuttgart, Germany
The direct increase of the spectral brightness of the short wavelengths spectra of the Sun from the longer wavelengths is still a very considerable challenge. The already existing examples of up-conversion, i.e., the generation of photons, notably spectrally blue-shifted to the wavelength of the excitation photons, like two-photon absorption, second (and higher order) harmonic generation, sequential multi-photon absorption, and the so called energy-transfer-upconversion in ion-doped glasses, are more often than not associated with the use of coherent light sources (lasers) and high intensities. Therefore, their application in direct sun-spectrum engineering and in solar cell devices is hard to realise.
We have investigated a method for upconversion of the longer wavelengths of the emission of the Sun towards shorter wavelengths by up-conversion fluorescence in two-component organic systems [1-3]. The very important advantages of this triplet-triplet annihilation supported bimolecular up-conversion process are in its inherent independence on the coherence of the excitation light [2] and the extremely low spectral brightness of the excitation source which is needed. We have realised non-coherent excitation intensity of 100 mWcm-2 collected from an excitation band with nearly ~ 80nm spectral width, i.e. spectral power density 125 µWnm-1, as well as using the terrestrial Sun emission [3].
We further present optimisation possibilities, concepts and results towards applications in organic and hybrid solar cells.
References
1. S. Baluschev, P. Keivanidis, T. Miteva, G. Nelles, U. Scherf, A. Yasuda, G. Wegner, Adv. Mat. 15, 2095 (2003)
2. S. Baluschev, T. Miteva, V. Yakutkin, G. Nelles, A. Yasuda, G. Wegner, Phys. Rev. Lett. 97, 143903 (2006)
3. S. Baluschev, V. Yakutkin, G. Wegner, T. Miteva, G. Nelles, A. Yasuda, S. Chernov, S. Aleshchenkov, and A. Cheprakov, Appl. Phys. Lett. 90, 181103 (2007)