Symmetrical Oxalate Derivative for Dual Interface-Grain Boundary Chelation Enabling High-Efficiency and Stable Perovskite Solar Cells

Perovskite surfaces exhibit defect densities ∼100× higher than the bulk, making interfacial recombination and instability critical challenges for perovskite solar cells (PSCs). Here, we introduced bis(2,4,5-trichloro-6-carbopentoxyphenyl) oxalate (BTCPPO), a novel oxalate derivative, at the perovskite/hole transport layer (HTL) interface. BTCPPO features a symmetric structure comprising a central oxalate group bridged to two phenyl rings with pentoxy ester tails, which enables secondary modification-induced local recrystallization in the upper perovskite film. Through chelation between its oxygen-containing groups and uncoordinated Pb 2+, BTCPPO reduces grain boundaries (GBs), enhances crystallinity, and passivates interfacial/GB defects, thereby prolonging charge-carrier lifetimes and suppressing nonradiative recombination. Additionally, BTCPPO fills GB voids, creating a smoother, superhydrophobic surface that impedes moisture/oxygen ingress while optimizing energy level alignment for efficient hole extraction. The resulting PSCs achieve a champion efficiency of 25.62% (negligible hysteresis) and retain ∼90% of their initial PCE after 3800 h in ambient conditions (∼30% RH), alongside exceptional thermal and illumination stability.