Self-assembled monolayers for tin perovskite solar cells: challenges and opportunities

Large-scale implementation of emerging halide perovskite solar cells (PSCs) has been restrained by environmental and health concerns stemming from the use of lead in their composition. In contrast, tin perovskite solar cells (TPSCs) have been widely recognized as viable alternatives owing to their ideal optical band gap, high carrier mobility and excellent optoelectronic properties. However, TPSCs encounter significant open-circuit voltage (V_oc) deficits due to the spontaneous oxidation of Sn²⁺ and uncontrolled crystallization process. Hence, self-assembled monolayers (SAMs) are now explored as a solution to optimize the perovskite/transport layer interface and improve V_oc. Despite the potential advantages and wide applications of SAMs in other optoelectronic devices, their application in TPSCs is relatively scarce. In this review, we elucidated the working mechanism of SAMs in improving device efficiency, summarized the recent progresses, and outlined the challenges in their application in TPSCs. We also discussed strategies for leveraging SAMs to mitigate the V_oc deficit in TPSCs. We hope that this review would offer a unique perspective for the ongoing research endeavors focused on the application of SAMs in TPSCs.