Isolating Chemical Reactivity of Perovskite/Transport Layer Interfaces to Advance Stability

Detailed understanding of the degradation pathways in perovskite solar cells will be essential to their deployment. Layers directly interfacing with the perovskite active layer are of particular importance due to the chemical reactivity of the organic A-site cation. However, the reactivity of the perovskite with the transport layer materials can vary widely depending on the interface chemical composition and its preparation. To systematically design more stable perovskite solar cells, the isolated, independent effect of each transport layer interface on stability should be understood. Here, we leverage a symmetric device stack with the same transport layer on each side to isolate the chemical reactivity of the perovskite with widely used electron and hole transporting materials, including NiO_x, SnO_x, and SAMs. We accomplish this by depositing perovskite atop the transport layer then diffusion bonding two such half-stacks using hot-pressing lamination, creating a self-encapsulated stack where the perovskite layer is sandwiched between identical transport layers. This symmetric design allows for light and heat durability testing of the perovskite with a single transport layer interface at a time. To evaluate relative durability, we subject the laminated stacks to 1-sun and 85°C elevated temperature conditions while recording degradation <i>in situ</i> via visible light imaging. Post-mortem analysis including PL, XRD, ATR-FTIR, and SEM reveal clear chemical trends in stability. From this foundational knowledge, we examine the tuning of the interface chemistries by atomic layer deposition to passivate the chemical reactivity. We find that targeted interface treatments can significantly reduce the reactivity of metal-oxide interfaces and dramatically extend perovskite stability.