Fused-ring isomerization dopant-free hole transport materials for high-performance inorganic perovskite solar cells

We synthesized two linear dopant-free hole transport materials (HTMs), denoted as NT and iNT, by coupling methoxytriphenylamine donor unit with either naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole or its isomeric counterparts naphtho[1,2-d:5,6-d']bis([1,2,3]thiadiazole) as acceptor units. The fused-ring isomerization structure of iNT endows it with a substantial dipole moment and well-aligned energy levels, which are highly favorable for efficient free-charge extraction. Compared to devices based on NT, CsPbI₃ inorganic perovskite solar cells (IPSCs) employing iNT exhibited significantly enhanced performance, achieving a power conversion efficiency (PCE) of 18.09%. Furthermore, the unencapsulated iNT-based devices demonstrated excellent operational stability.