The efficiency of antimony selenide (Sb2 Se3 ) solar cells is still limited by significant interface and deep-level defects, in addition to carrier recombination at the back contact surface. This paper investigates the use of lithium (Li) ions as dopant for Sb2 Se3 films, using lithium hydroxide (LiOH) as a dopant medium. Surprisingly, the LiOH solution not only reacts at the back surface of the Sb2 Se3 film but also penetrate inside the film along the (Sb4 Se6 )n molecular chain. First, the Li ions modify the grain boundary's carrier type and create an electric field between p-type grain interiors and n-type grain boundary. Second, a gradient band structure is formed along the vertical direction with the diffusion of Li ions. Third, carrier collection and transport are improved at the surface between Sb2 Se3 and the Au layer due to the reaction between the film and alkaline solution. Additionally, the diffusion of Li ions increases the crystallinity, orientation, surface evenness, and optical electricity. Ultimately, the efficiency of Sb2 Se3 solar cells is improved to 7.57% due to the enhanced carrier extraction, transport, and collection, as well as the reduction of carrier recombination and deep defect density. This efficiency is also a record for CdS/Sb2 Se3 solar cells fabricated by rapid thermal evaporation.
Keywords: Li gradient field; Sb2Se3; carrier collection; deep-level defect; gradient band structure.
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