Abstract
Although texturing of the transparent electrode of thin-film solar cells has long been used to enhance light absorption via light trapping, such texturing has involved low aspect ratio features. With the recent development of nanotechnology, nanostructured substrates enable improved light trapping and enhanced optical absorption via resonances, a process known as photon management, in thin-film solar cells. Despite the progress made in the development of photon management in thin-film solar cells using nanostructures substrates, the structural integrity of the thin-film solar cells deposited onto such nanostructured substrates is rarely considered. Here, we report the observation of the reduction in the open circuit voltage of amorphous silicon solar cells deposited onto a nanostructured substrate with increasing areal number density of high aspect ratio structures. For a nanostructured substrate with the areal number density of such nanostructures increasing in correlation with the distance from one edge of the substrate, a correlation between the open circuit voltage reduction and the increase of the areal number density of high aspect ratio nanostructures of the front electrode of the small-size amorphous silicon solar cells deposited onto different regions of the substrate with graded nanostructure density indicates the effect of the surface morphology on the material quality, i.e., a trade-off between photon management efficacy and material quality. This observed trade-off highlights the importance of optimizing the morphology of the nanostructured substrate to ensure conformal deposition of the thin-film solar cell.
Highlights
IntroductionTexturing of the transparent electrode of thin-film solar cells ( amorphous silicon solar cells) has long been used to enhance light absorption (and the conversion efficiency) via light trapping, such texturing has involved low roughness (i.e., structures with heights less than100 nm) and is limited regarding the degree of light absorption enhancement that is possible in thin-film solar cells (see, e.g., Reference [1])
Texturing of the transparent electrode of thin-film solar cells has long been used to enhance light absorption via light trapping, such texturing has involved low roughness and is limited regarding the degree of light absorption enhancement that is possible in thin-film solar cells
The higher aspect ratio structures that can be produced are advantageous for enhancing the light absorption in thin-film solar cells with very thin absorber layers, e.g., amorphous silicon (a-Si) solar cells deposited onto a nanostructured substrate comprised of an array of nanopillars
Summary
Texturing of the transparent electrode of thin-film solar cells ( amorphous silicon solar cells) has long been used to enhance light absorption (and the conversion efficiency) via light trapping, such texturing has involved low roughness (i.e., structures with heights less than100 nm) and is limited regarding the degree of light absorption enhancement that is possible in thin-film solar cells (see, e.g., Reference [1]). Of the wide variety of approaches to perform photon management in thin-film solar cells, one attractive approach is the use of nanostructured substrates with an array of nanostructures of high aspect ratio that have greater height from the substrate; such a nanostructured morphology manifests itself in the subsequently deposited thin-film solar cell, thereby allowing improved optical absorption [2,3,4,5,6,7,8]. The higher aspect ratio structures that can be produced are advantageous for enhancing the light absorption in thin-film solar cells with very thin absorber layers, e.g., amorphous silicon (a-Si) solar cells deposited onto a nanostructured substrate comprised of an array of nanopillars (see e.g., [5]). Because of the “folded” morphology of the subsequently deposited thin-film solar cell on the nanostructured substrate, typically based on a p-n or p-i-n junction semiconductor device, we refer to such a device as a “folded junction” solar cell [2,3,4]
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