Development of encapsulation strategies towards the commercialization of perovskite solar cells

After a decade of research and development on the perovskite solar cells (PSCs), the achievements targeting the device stability have fallen far behind the progress made in the photoelectric conversion efficiency, which plays as the major obstacle for their commercialization. Although the in-depth understanding of the origin of intrinsic and extrinsic degradation mechanisms is being rapidly acquired for the materials, device architecture and module, along with the synthetic strategies developed to improve the stability of functional layers within the device to inhibit phase and crystal structure transition, ion migration, morphology degradation, surface and bulk chemical reaction, a consensus is forming that a systematic encapsulation is indispensable in the device and module architecture to effectively resist harsh outdoor ageing factors. This review, by focusing on the fundamental and technological development in the encapsulation studies of PSCs, discusses the role of encapsulation in a common sense against the moisture and oxygen intrusion, which relies mainly on the selection of encapsulation materials and the optimization of encapsulation architecture, and a more broadened sense of encapsulation to avoid lead leakage and improve the intrinsic stabilities of various materials in the device. Therefore, this review first summarizes the current state-of-the-art encapsulation approaches in various optoelectronic devices (light-emitting diode, organic photovoltaic cell, silicon solar cell) for their possible implications for the PSCs. Then, targeting the moisture and oxygen stability, photostability and thermal stability, damp-heat stability, and thermal cycling stability, this review highlights the impact of encapsulation specifically on these stabilities. Furthermore, the authors advocate the establishment of standard and consistent procedures for the assessment of encapsulation materials and the stability of encapsulated devices for a more quantificational investigation and comparison. Finally, it summarizes current encapsulation materials in diversified techniques by developing a systematic concept of encapsulation, namely the internal encapsulation, such as the grain boundary encapsulation, surface and interface encapsulation, and device-level external encapsulation. The review thus offers an outlook on future material design, which may hopefully inspire the future development of encapsulation technologies for PSCs.