Cross-linked multifunctional bilayer polymer buffer for enhanced efficiency and stability in perovskite solar cells

Addressing the stability challenges induced by the chemical interactions between metal electrodes and perovskite components is essential for high-performance perovskite solar cells (PSCs). Herein, we design a bilayer multifunctional polymer buffer composed of polyethyleneimine (PEI) and 2-((2-methyl-3-(2-((2-methylbutanoyl)oxy)ethoxy)-3-oxopropyl)thio)-3-(methylthio)succinic acid (PDMEA), inserting into the interface of metal electrode/transporting layer. This buffer mitigates metal atom diffusion by forming thioether-metal-carboxyl chelation rings between the metal layer and PDMEA. Additionally, it facilitates efficient electron transport and suppresses interfacial recombination through an in-situ cross-linking between the carboxyl groups of PDMEA and the amine groups of PEI based on Lewis acid-base reaction. Consequently, this design effectively reduces undesirable metal/ion interdiffusion during device fabrication and operation. The resulting PSCs with the PEI/PDMEA buffer achieve certified power conversion efficiencies (PCEs) of 26.46% (0.1 cm²) and 24.70% (1.01 cm²), demonstrating enhanced thermal and operational stability. We anticipate that this buffer design strategy, which forms bilayer polymer buffers via cross-linking of polymers with distinct functionalities, will inspire the rational design of robust buffers for highly efficient and stable PSCs and other electronic devices.