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Typically n‐i‐p structured perovskite solar cells (PSCs) incorporate 2,2′,7,7′‐tetrakis (N,N‐di‐p‐methoxyphenyl amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as the hole‐transporting material. Chemical doping of spiro‐OMeTAD involves a lithium bis(trifluoromethyl sulfonyl)imide dopant, causing complex side‐reactions that affect the device performance, which are not fully understood. Here, we investigate the aging‐dependent device performance of widely used formamidinium lead triiodide (FAPbI3)‐based PSCs correlated with lithium‐ion (Li+) migration. Comprehensive analyses reveal that Li+ ions migrate from spiro‐OMeTAD to perovskite, SnO2, and their interfaces to induce the phase‐back conversion of α‐FAPbI3 to δ‐FAPbI3, generation and migration of iodine defects, and de‐doping of spiro‐OMeTAD. The rapid performance drop of FAPbI3‐based PSCs, even aging under dark conditions, is attributed to a series of these processes. This study identifies the hidden side effects of Li+ ion migration in FAPbI3‐based PSCs that can guide further work to maximize the operational stability of PSCs.image

For the fabrication of thin-film electronics, conventional physical vapor deposition (PVD) processes have been widely used to form metal contacts on various thin films. However, the PVD process, involving thermally activated high-energy metal atoms, damages the underlying thin films, severely deteriorating the performance and stability of the device. The van der Waals (vdW) metal-contact approach has recently emerged to avoid this issue. By transferring predeposited metal contacts using vdW interactions, atomically sharp and electronically clean heterointerfaces can be formed without generating unintended defects. In this article, we review the fundamentals, processes, and various applications of the vdW metal-integration approach. The classical theory of vdW interactions is first reviewed, followed by the introduction of various approaches for constructing vdW metal contacts on thin films. Subsequently, the influence of contact configuration on the performance of various applications is summarized. Finally, the remaining challenges and prospects are discussed for the practical usage and versatile application of vdW metal contacts for next-generation electronic devices.