High roughness Ag back reflector on a metal underlayer for thin film solar cell applications

• High roughness Ag film was obtained by introducing metal (Al and Cu) underlayers.
• Increase of Ag film roughness on Al underlayer is attributed to Ag–Al alloying.
• Rough Ag films enhance the light trapping by decreasing reflectance of incoming light.
• Ag–Al alloy phase was controlled by varying thickness of Al underlayer and Ag film.
• Ag–Al alloy film with 75–118 nm roughness was obtained at a low temperature, 350 °C.

The roughness development of Ag film was investigated for potential as a back reflector material in thin film solar cells on flexible stainless steel (STS) substrates. The influence of metal underlayers was evaluated in order to obtain a rough Ag film at a low deposition temperature (≤400 °C). By depositing Ag on a 100 nm Al underlayer to induce Ag–Al alloying, the film roughness was increased three times more than that of Ag films on bare STS at 400 °C. The Ag film deposited on an Al underlayer at 350 °C exhibited 75 nm roughness and uniformly distributed crystallites, which was effective for visible light scattering. The Ag–Al alloy phase was also controlled using the thickness ratio of Ag and Al. The present work clearly demonstrated that an Ag back reflector film with a higher roughness could be fabricated through inserting a metal underlayer at a deposition temperature much lower than the 500 °C that has been reported in earlier works.

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