A regioisomeric phenanthroquinoxaline-based small molecular defect passivation layer for enhanced efficiency in stable perovskite solar cells

Abstract

Solution processability and temperature-induced fast crystallization lead to various defects at the surface of perovskite films, which act as the epicenters of non-radiative recombination loss. Therefore, eliminating these surface defects through effective passivation is of utmost importance. Herein, we introduce two small-molecular donor–acceptor–donor (D–A–D) interface passivators, namely, 4,4′-(dipyrido[3,2-a:2′,3′-c]phenazine-10,13-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (PNQP) and 4,4′-(dipyrido[3,2-a:2′,3′-c]phenazine-11,12-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (PNQO), by varying the substitution position of the donor triphenylamine motifs. By simply relocating the donor arms in PNQO, the π-conjugated heterocyclic core is pushed outward, establishing direct contact with the perovskite surface and significantly strengthening the perovskite/HTM interfacial interaction while reducing interfacial defect recombination. For PNQO, the enhanced dipole moment leads to a better charge-separated state and improved hole mobility, facilitating the healing of surface defects by chelating with uncoordinated Pb²⁺ through a Lewis acid–base interaction. The modulation of regioisomeric configurations to enhance passivation efficacy has been systematically investigated through a combination of comprehensive theoretical and experimental approaches. Remarkably, the PNQO-treated PSCs delivered a champion power conversion efficiency (PCE) of 31.50% under an indoor 1000 lx white LED, which is higher than that of the control device without passivation layer treatment (25.32%). In addition, the PNQO-treated PSCs exhibited an improved PCE of 18.74% under AM 1.5G illumination, which is higher than that of the control device (16.64%). After 1560 hours of storage under ambient conditions, the unencapsulated device retained 91% of its initial PCE, outperforming the control device, which could achieve only 41%. This study establishes a design strategy for a small molecular passivation layer to enhance the efficiency and stability of PSCs in the future.