Understanding the dopant of hole-transport polymers for efficient inverted perovskite solar cells with high electroluminescence

Poly(triarylamine) (PTAA) is a promising hole transport polymer for efficient inverted perovskite solar cells (PSCs) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is an indispensable dopant for PTAA. However, the interplay between PTAA and F4TCNQ and its effects on the device operation of PSCs are still unknown. Herein, the fundamental interaction between PTAA and F4TCNQ was systematically studied using a combination of extensive theoretical calculations and detailed experimental approaches. The results reveal that the π-π stacking formed between PTAA and F4TCNQ was favorable for improving the spatial configuration of PTAA and the charge transfer between PTAA and F4TCNQ. Meanwhile, a C ≡ N⋯Pb²⁺ coordination bond and N-H⋯N hydrogen bond could be built between F4TCNQ and perovskites, substantially improving the quality of perovskite films and the interfacial properties between perovskite and PTAA and thus enhancing hot-carrier injection. Consequently, an inverted PSC fabricated with PTAA doped with F4TCNQ yielded a high efficiency of up to 22.5% and demonstrated high electroluminescence with an external quantum efficiency of 4.6%. Meanwhile, PSCs showed good stability under continuous illumination and thermal conditions. This work offers a deeper understanding of the interplay between the dopant and hole transport polymer and highlights the important design criterion of dopants for hole transport polymers toward the higher photovoltaic performance of PSCs.