Perovskite solar cells (PSCs) and organic photovoltaics (OPVs) have undergone rapid development within the last decade, exhibiting exciting properties such as high efficiency, flexibility, and the potential for large‐scale fabrication through roll‐to‐roll (R2R) processing. Despite this, operational stability is recognized to be an ongoing challenge as prolonged device lifetimes are scarcely observed. This instability can be narrowed down to both “intrinsic degradation” and “extrinsic degradation,” with exposure to moisture and oxygen having detrimental effects on device performance. A means of delaying the degradation of flexible PSC and OPV devices is through barrier encapsulation. Despite glass encapsulation exhibiting ideal barrier properties, the potential for flexible devices and high‐throughput R2R fabrication requires the development of flexible barrier materials and encapsulation strategies. These barriers must demonstrate outstanding moisture permeation resistance, high transparency, chemical and thermal stability, and must be able to withstand repeated mechanical deformation. Herein, the fundamental principles of PSC and OPV devices are initially discussed, highlighting the degradation mechanisms and current stability obstacles. A review of the latest flexible barrier materials and encapsulation strategies follows, introducing stability studies that have been undertaken on flexible PSCs and OPV, along with suggestions as to the direction that future research may take.

Perovskite solar cells (PSCs) are attracting widespread attention due to their exceptional photovoltaic performance and their potential for large‐scale production via low‐cost, high‐throughput roll‐to‐roll (R2R) methods. Full realization of this production approach requires replacement of the evaporated metal electrode commonly used in PSCs. Here, a novel vacuum‐free R2R‐compatible method is introduced to fabricate and deposit printed electrodes based on electrically conductive pastes, which avoids potential loss of PSC performance due to solvent migration from the pastes. Flexible R2R‐fabricated PSCs with record power conversion efficiencies (PCEs) of up to 16.7% are produced by vacuum‐free deposition of all functional layers, apart from the transparent conductive electrode. This performance compares very favorably with that of control flexible PSCs comprising an evaporated gold electrode, which displays PCEs of up to 17.4%. Furthermore, the PSCs comprising a printed electrode demonstrate outstanding operational and mechanical stability, with negligible loss of PCE after 24 h of continuous 1‐sun illumination and retention of more than 90% of their initial PCE after 3000 cyclic bends.