Abstract
A thin-film solar cell with dual photonic crystals has been proposed, which shows an advanced light-trapping effect and superior performance in ultimate conversion efficiency (UCE). The shapes of nanocones have been optimized and discussed in detail by self-definition. The optimized shape of nanocone arrays (NCs) is a parabolic shape with a nearly linearly graded refractive index (GRI) profile from the air to Si, and the corresponding UCE is 30.3% for the NCs with a period of 300 nm and a thickness of only 2 μm. The top NCs and bottom NCs of the thin film have been simulated respectively to investigate their optimized shapes, and their separate contributions to the light harvest have also been discussed fully. The height of the top NCs and bottom NCs will also influence the performances of the thin-film solar cell greatly, and the result indicates that the unconformal NCs have better light-trapping ability with an optimal UCE of 32.3% than the conformal NCs with an optimal UCE of 30.3%.
Highlights
Due to the abundance and a nonpoisonous feature, Si-based solar cells are still dominating the photovoltaic market
The reflectance in the short wavelength region (300 ~ 600 nm) decrease as the b/a increase, and it reaches to the minimum when b/a = 1.0, which can be attributed to the graded refractive index (GRI) effect [17]
In conclusion, we have proposed a novel method for defining the shape of nanocone arrays (NCs) structures by a new equation
Summary
Due to the abundance and a nonpoisonous feature, Si-based solar cells are still dominating the photovoltaic market. As silicon is a kind of an indirect band gap material, the light absorption of Si is poor. The cost of bulk of Si solar cells is high, which hinders the commercialization of Si solar cells. To overcome this problem, thin-film solar cells have been proposed, which reduces the cost of Si solar cells and improves the collection of carriers because of the reduced diffusion length [1]. The reduction of the thickness of Si solar cells leads to poor absorption of the longer wavelengths (near the band gap) [2]. The dual photonic crystal cells have great potentials in the field of light harvesting. The influences of the shapes and the heights of the top NCs and bottom NCs on the light-trapping performance have not been investigated and discussed systematically
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