Spontaneous Perovskite Passivator Featuring Dual Functional Groups

ABSTRACT A recent advancement in perovskite solar cells (PSCs) is the emergence of spontaneous heterointerface modulators (SHMs), which eliminate the additional processing required for conventional heterointerface modification. Among SHMs, alkyl‐primary‐ammonium‐bis(trifluoromethylsulfonyl)imides (RA‐TFSIs), used as hole‐transport material (HTM) additives, enable spontaneous perovskite passivation. Upon HTM deposition, RA cations passivate the perovskite surface through strong adsorption via the ammonium (NH 3 + ) moiety. However, conventional RA‐TFSIs only passivate A ‐site defects, limiting their effectiveness. Moreover, RA components with multiple functional groups have not been explored. Here, we propose a strategy to suppress multiple defect sites using a spontaneous passivator with dual functional groups. 2‐thiophene‐ethyl‐ammonium‐TFSI (TEA‐TFSI) is newly synthesized and verified as a spontaneous perovskite passivator for n–i–p PSCs employing thermally stable poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) as the HTM. Spontaneous passivation using TEA‐TFSI forms a monolayer‐like overlayer, where TEA cations are adsorbed at both A ‐ and X ‐site defects via ammonium and thiophene moieties, respectively, overcoming the single‐site limitation of RA‐TFSIs. The TEA overlayer also improves PTAA adhesion. Consequently, PSCs achieve power conversion efficiencies of 22.2% (≈0.12 cm 2 minicells) and 21.7% (≈1.6 cm 2 minimodules, active area: 1.41 cm 2 ), respectively, with thermal stability. This work establishes a general design principle for multifunctional spontaneous passivators and advances materials science.