Multidirectional Light‐Harvesting Enhancement in Dye Solar Cells by Surface Patterning

Abstract

purpose in other types of thin fi lm solar cells, [3][4][5][6][7] their integration in DSCs has been delayed until recently as a result of the diffi culties that arise when optical materials are combined with the usually employed TiO 2 (anatase) pastes and corrosive electrolytes used in DSCs. The design of materials ad hoc has allowed overcoming these obstacles and high expectations are now being put on them. Conventionally, large anatase particles acting as scattering centres [8][9][10] have been employed to trap freely propagating photons into the photoanode by multiple scattering. This optical phenomenon gives rise to a large enhancement of the light harvesting effi ciency, but also implies that the DSC turns opaque. Motivated originally by the possibility to take advantage of slow photon effects, and later by that of preserving transparency in cells of enhanced effi ciency, different periodic architectures with photonic crystal properties have been proposed. [11][12][13][14] In this case, the primary mechanism of improvement is the back refl ection of light frequencies that falls within the photonic band gap, although different types of optical resonances have been shown to contribute to the enhancement as well. [ 15,16 ] In all these approaches, as they are based on diffuse or specular back refl ection, the improvement of performance when light reaches the cell from the front side is inevitably accompanied by a decrease of the efficiency when light comes from the counter electrode. As an alternative to these approaches, very recently, relief patterns have been moulded onto the surface of nanocrystalline anatase fi lms with the aim of diffracting unabsorbed light back into the electrode with an oblique angle. Initially reported results prove the potential of this approach to largely increase the light harvesting effi ciency without adding any extra layer to the cell. [17][18][19][20] Besides, these results indicate that it should be possible to improve effi ciency while preserving the multidirectional operation of the cell (i.e., under front and rear illumination conditions), as the nanostructured surface of a transparent material behave as diffracting interface and, hence, as potential absorption enhancer at any angle of incidence of light on its surface.In this work, we demonstrate that surface relief patterns can be used as multidirectional enhancers of the effi ciency of DSC. We used a combination of soft-lithography and micro-stamping One dimensional gratings patterned on the surface of nanocrystalline titania electrodes are used as a light harvesting strategy to improve the overall performance of dye solar cells under both frontal and rear illumination conditions. A soft-lithography-based micromoulding approach is employed to replicate a periodic surface relief pattern onto the surface of the electrode, which is later sensitized with a dye. As the patterned surface acts as an optical grating both in refl ection and transmission modes, its effect is to increase the light path of diffracted beams within ...

Enhanced Directional Light Extraction from Patterned Rare‐Earth Phosphor Films

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Efficient bifacial dye-sensitized solar cells through disorder by design

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A Comparative Study on the Photoresist Patterning of Glass and Silicon With Microholes via Maskless Photolithography

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