Improved Mechanical Adhesion and Durability Enabled by Bilayer Hole Transport Layers in Perovskite Solar Cells

We investigate the mechanical integrity of various types of self-assembled monolayers (SAMs) and NiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> and metal halide perovskite half-cells incorporating these hole transport layers (HTLs). Through macroscopic and microscopic techniques, we quantify interfacial fracture energies (G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf>) and identify failure points within device stacks susceptible to delamination. Importantly, our results reveal a significant improvement in mechanical reliability through significantly improved G<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> when a SAM is deposited on NiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>. Additionally, the use of solution-processed perovskite on NiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> layers that have low internal bonding compared to fully evaporated material stacks maintains the enhanced mechanical robustness for the overall stack. These findings underscore the role of NiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> in reinforcing interfacial adhesion within perovskites and provide valuable insights into the design of mechanically robust perovskite solar cells.