Suppressing Electrode Diffusion With a PMMA Metal-Capture Mesh Enables Stable Conventional Organic Photovoltaics.

Conventional organic photovoltaics (OPVs) often suffer from premature failure because top-electrode metals diffuse into the organic stack under thermal stress, generating interfacial traps and leakage pathways. Here, we identify severe aging-driven Ag diffusion as a critical failure pathway in high-efficiency conventional architectures. To suppress this without compromising charge extraction, we introduce polymethyl methacrylate (PMMA) that self-assembles into a discontinuous, mesh-like network on the PDINN layer, functioning as both a physical diffusion barrier and a chemical metal-capture mesh. Spectroscopic analyses reveal that PMMA carbonyl groups coordinate with Ag through Ag-O interactions, providing chemical immobilization that complements the physical barrier in blocking thermally activated, concentration-gradient-driven migration. Therefore, PMMA-modified devices deliver a power conversion efficiency (PCE) of 20.2% with markedly enhanced stability: they retain >80% of the initial PCE after 3,574 h under ISOS-D-1I shelf storage, show a T80 of 105 h under ISOS-D-2I thermal aging at 85°C, compared with only 10 h for control devices, and retain 70.1% after 94 h under ISOS-L-3 conditions (1 sun, 65°C, 50% relative humidity), versus 51.4% for controls. This strategy also improves the thermal stability of Cu- and Au-based devices, establishing a broadly applicable interfacial concept for mitigating electrode-diffusion-induced failure in high-efficiency conventional OPVs.