Molecular engineering of contact interfaces for high-performance perovskite solar cells

Metal-oxide-based charge-transport layers have played a pivotal role in the progress of perovskite solar cells. Yet metal-oxide/perovskite interfaces are often highly defective, owing to both metal-oxide and perovskite surface defects. This results in non-radiative recombination and impedes charge transfer. Moreover, during operation, such interfaces may suffer from undesirable chemical reactions and mechanical delamination issues. Solving this multifaceted challenge requires a holistic approach to concurrently address the interfacial defect, charge-transfer, chemical stability and delamination issues, to bring perovskite solar cell technology closer to commercialization. With this motivation, we review and discuss the issues associated with the metal-oxide/perovskite interface in detail. With this knowledge at hand, we then suggest solutions based on molecular engineering for many, if not all, challenges that encumber the metal-oxide/perovskite interface. Specifically, in light of the semiconducting and ultrafast charge-transfer properties of dyes and the recent success of self-assembled monolayers as charge-selective contacts, we discuss how such molecules can potentially be a promising solution for all metal-oxide/perovskite interface issues. In perovskite solar cells, metal-oxide/perovskite interfaces suffer from a combination of issues related to interfacial defects, charge transfer, chemical stability and delamination, limiting performance. This Review discusses how molecular engineering of metal-oxide/perovskite interfaces with self-assembled monolayers can provide a solution and help to bring perovskite solar cells to market.