Rational Design of Rhodanine-Based Hole-Selective Layers for Optimizing Interfacial Passivation in High-Performance...

Wide-bandgap (WBG) perovskite solar cells (PSCs) are promising candidates for indoor photovoltaics (IPVs), but their efficiency is limited by non-radiative recombination at the buried perovskite/transport layer interface. To reduce these losses, this study proposes using self-assembled monolayers (SAMs) combining a triphenylamine (TPA) donor with rhodanine (RH) or rhodanine-3-acetic acid (RA) anchoring groups, as effective hole-selective layers (HSLs). Using NiOx/SAM double HSLs, we found that the heteroatom-rich RA group with a carboxymethyl co-anchor enhances NiOx surface oxidation and provides strong interfacial passivation. DFT calculations, electrochemical analysis, and characterization via XPS, UPS, PL, and SEM were used to elucidate the HSL-perovskite interface relationship. Structural studies revealed that the molecular spacer influences perovskite growth. Sterically hindered TPA-AN-RA yields smaller grains with more defects, while planar TPA-PH-RA enables larger grains and fewer traps. The optimized TPA-RA structure ensures balanced energetics and improved charge extraction, delivering an impressive indoor iPCE of 41.81% under a 1000 lux white LED. Under AM 1.5G conditions, it achieves 18.68% PCE, making it suitable for hybrid lighting environments. Furthermore, the unencapsulated TPA-RA device retained 84% of its indoor efficiency after 1600 h in an inert atmosphere, demonstrating excellent intrinsic stability. This work highlights the potential of molecular engineering for producing high-efficiency stable indoor PSCs.