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.