Thin film solar cells (TFSCs) suffer from poor light absorption due to their small thickness, which limits most of their practical applications. Surface plasmons generated by plasmonic nanoparticles offer an opportunity for a low-cost and scalable method to optically engineer TFSCs. Here, a systematic simulation study is conducted to improve the absorption efficiency of amorphous silicon (a-Si) by incorporating double sided plasmonic bi-metallic (Al-Cu) nanogratings. The upper pair of the gratings together with an antireflection coating are responsible for minimizing the reflection losses and enhancing the absorption of low wavelength visible light spectrum in the active layer. The bottom pairs are accountable for increasing the absorption of long wavelength photons in the active layer. In this way, a-Si, which is a poor absorber in the long wavelength region, is now able to absorb broadband light from 670-1060 nm with an average simulated absorption rate of more than 70%, and improved simulated photocurrent density of 22.30 mA cm-2, respectively. Moreover, simulation results show that the proposed structure reveals many other excellent properties such as small incident angle insensitivity, tunability, and remarkable structural parameters tolerance. Such a design concept is quite versatile and can be extended to other TFSCs.
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