Resist Thermal Shock Through Viscoelastic Interface Encapsulation in Perovskite Solar Cells

Enhancing the lifetime of perovskite solar cells (PSCs) is one of the essential challenges for their industrialization. Although the external encapsulation protects the perovskite device from the erosion of moisture and oxygen under various harsh conditions. However, the perovskite devices still undergo static and dynamic thermal stress during thermal and thermal cycling aging, respectively, resulting in irreversible damage to the morphology, component, and phase of stacked materials. Herein, the viscoelastic polymer polyvinyl butyral (PVB) material is designed onto the surface of perovskite films to form flexible interface encapsulation. After PVB interface encapsulation, the surface modulus of perovskite films decreases by nearly 50%, and the interface stress range under the dynamic temperature field (−40 to 85 °C) drops from −42.5 to 64.8 MPa to −14.8 to 5.0 MPa. Besides, PVB forms chemical interactions with FA⁺ cations and Pb²⁺, and the macroscopic residual stress is regulated and defects are reduced of the PVB encapsulated perovskite film. As a result, the optimized device's efficiency increases from 22.21% to 23.11%. Additionally, after 1500 h of thermal treatment (85 °C), 1000 h of damp heat test (85 °C & 85% RH), and 250 cycles of thermal cycling test (−40 to 85 °C), the devices maintain 92.6%, 85.8%, and 96.1% of their initial efficiencies, respectively.