Abstract
ABSTRACTThe Lambertian limit represents a benchmark for the enhancement of the effective path length in solar cells, which is important as soon as the absorption length exceeds the absorber thickness. In previous publications it has been shown that either extremely thick or extremely thin solar cells can be driven close to this limit by exploiting up to date photon management. In this contribution we show that the Lambertian limit can also be achieved with thin-film solar cells based on amorphous silicon for practically relevant absorber thicknesses. Departing from superstrates, which are currently incorporated into state-of-the-art thin-film solar cells, we show that their topology has simply to be downscaled to typical feature sizes of about 100 nm in order to achieve this goal. By systematically studying the impact of the modulation height and the lateral feature sizes of the incorporated textures and of the absorber thickness we are able to deduce intuitive guidelines how to approach the Lambertian limit in randomly textured thin-film solar cells.
Highlights
Thin-film solar cells are considered to be attractive candidates for photovoltaic elements
To date the most common approach for an efficient light trapping in amorphous silicon (aSi):H is the use of textured surfaces made of a transparent conductive oxide (TCO)
We considered the commercially available superstrate Asahi-U, superstrates fabricated in Neuchatel [24] and in Julich [25]
Summary
Thin-film solar cells are considered to be attractive candidates for photovoltaic elements. To date the most common approach for an efficient light trapping in aSi:H is the use of textured surfaces made of a transparent conductive oxide (TCO) The purpose of these textures is to reduce reflection losses and to enhance the scattering of light, which leads to an effectively enhanced optical path length in the solar cell. For a Lambertian scattering texture, it was shown that the maximum achievable path length enhancement in the weakly absorbing limit amounts to 4n2, with n being the refractive index of the absorbing material [12] This Lambertian limit, called Yablonovitch limit, constitutes a referential benchmark for every possible light trapping scheme. These materials can be sputtered onto the superstrate and afterwards etched [18], or grown with chemical vapor deposition [19]. To evaluate the performance of the textures, we calculated the absorptance of the corresponding solar cell implemented as in Fig. 1(a) for 111 distributed wavelengths between 300 and 850 nm
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