Photovoltaic properties of PSi impregnated with eumelanin
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NANO EXPRESS
Open Access
Photovoltaic properties of PSi impregnated with eumelanin Guido Mula1*, Laura Manca1, Susanna Setzu1 and Alessandro Pezzella2
Abstract A bulk heterojunction of porous silicon and eumelanin, where the columnar pores of porous silicon are filled with eumelanin, is proposed as a new organic-inorganic hybrid material for photovoltaic applications. The addition of eumelanin, whose absorption in the near infrared region is significantly higher than porous silicon, should greatly enhance the light absorption capabilities of the empty porous silicon matrix, which are very low in the low energy side of the visible spectral range (from about 600 nm downwards). The experimental results show that indeed the photocarrier collection efficiency at longer wavelengths in eumelanin-impregnated samples is clearly higher with respect to empty porous silicon matrices. Keywords: Organic-inorganic interface, Hybrid material, Bulk heterojunction, Eumelanin, Porous silicon, Photoconversion, 5,6-dihydroxyindole PACS: 88.40.fh, 88.40.jj
Background The relevance of solar power in the renewable energy field is constantly increasing due to its ready availability and to the fact that the available amount exceeds by several orders of magnitude the needs of the human race. The search for new materials with better performances than standard Si-based solar cells is also constantly increasing. Organic materials [1] emerged as a very attractive solution for this scope, their lower efficiencies with respect to inorganic materials being compensated by lower fabrication costs and higher flexibility. Hybrid materials have also been investigated as a way to combine the low production costs of organic materials with the high efficiency of inorganic materials [2-8]. Among the adopted strategies for new materials, interface geometry often plays a major role in the collection of photogenerated carriers, and bulk heterojunctions [3,9-12] - intimately mixing the two junction materials while keeping them separate in a ‘fractal like’ highsurface interface - are a very promising design for solar cells. This concept was introduced in the mid 1990s for
* Correspondence: [email protected] 1 Dipartimento di Fisica, Cittadella Universitaria di Monserrato, Università degli Studi di Cagliari, S.P. 8 km 0.7, Monserrato (Ca) 09042, Italy Full list of author information is available at the end of the article
organic solar cells [5,13-15] to shorten the exciton travel distance from the photon absorption site towards the charge-separating interface and then both to reduce the spontaneous recombination and to increase the collection efficiency. The very large interfacial area available for charge separation processes also increases the carrier collection efficiency. We investigate here a new hybrid material for photovoltaic applications composed by n-type porous silicon (PSi) and eumelanin, a natural pigment featuring relatively high electrical conductivity [16] and believed to rely mainly on proton-based conduction [16-18]. Porous Si is a large
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