Interface engineering in perovskite solar cells via DTP-OMe-2Br-modified Spiro-OMeTAD

Perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies (PCEs) exceeding 27 %, yet their long-term operational stability remains a significant barrier to commercialization. The state-of-the-art hole transport layer (HTL) based on Spiro-OMeTAD relies on hygroscopic lithium salts and volatile co-additives to boost conductivity, which inevitably accelerates interfacial degradation. Here, we introduce a molecular co-doping strategy in which a brominated dithieno[3,2-b:2′,3′-d]pyrrole derivative (DTP-OMe-2Br) is incorporated into Spiro-OMeTAD to synergistically combine their advantages. Owing to its planar donor-rich framework and bromine functionalities, DTP-OMe-2Br preferentially localizes at the perovskite/HTL interface, enhancing hole mobility, passivating undercoordinated Pb²⁺ defects, and increasing hydrophobicity without disrupting Spiro’s film-forming properties. As a result, devices achieve a champion PCE of 24.41 %, surpassing the 23.06 % of the pristine Spiro-OMeTAD reference, and retain over 85 % of their initial efficiency after 2500 h in ambient air. This work demonstrates that rationally designed small-molecule additives can serve as multifunctional interfacial modifiers for hybrid HTLs, offering a generalizable route toward high-efficiency and durable PSCs.