Molecular Dipole Buffer Layer Enabling Compact Interfaces in Perovskite Solar Cells

Despite advances in p-i-n perovskite solar cells, interfacial losses between the electron transport layer (ETL) and metal electrode remain a bottleneck for efficiency and stability. Bathocuproine (BCP), a common buffer layer, suffers from poor film uniformity, low electron mobility, and limited thermal stability. Here, we report BTI-N, a D–A–D-type small molecule featuring a benzo[c][1,2,5]thiadiazole core and polar N,N-dimethylamino groups. BTI-N exhibits favorable molecular packing and solubility, enabling compact, uniform films with efficient electron transport. The polar termini anchor Ag electrodes via Ag–N dipole formation, lowering the work function and improving band alignment and charge extraction. BTI-N also suppresses Ag and I ion diffusion, significantly enhancing thermal stability. We demonstrate broad compatibility across ETLs (C₆₀, PCBM), electrodes (Ag, Au), and perovskites with bandgaps from 1.58 to 1.7 eV. This work provides a practical interface engineering strategy to replace BCP and realize high-performance, stable perovskite solar cells.