A Review on Emerging Barrier Materials and Encapsulation Strategies for Flexible Perovskite and Organic Photovoltaics

Abstract 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.