Electrophilic molecule-induced π–π interactions reduce energy disorder of the hole transport layer for highly efficient perovskite solar modules

Abstract

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) is commonly used as a co-hole transport layer in inverted perovskite solar cells (PSCs). It can effectively improve the hole transport capability of NiO_x and obstruct the interfacial reaction between NiO_x and the perovskite. However, energy disorder and high hydrophobicity of PTAA will affect charge transport and superior perovskite film formation, further limiting the enhancement in efficiency and stability of PSCs. To address these issues, co-assembled electrophilic molecules with PTAA are explored to reduce the energy disorder and enhance the quality of heterojunction interface. Among the electrophilic molecules, 2,6-difluoro-3-nitrobenzonitrile (FCNO₂), showing the maximal electrophilic capability as evidenced by first principles calculations, effectively promotes molecular stacking by establishing the strongest π–π interactions with PTAA. The interactions promote charge transfer between PTAA and FCNO₂, further improving the hole mobility and energy level, and reordering the molecular chains, thus reducing the energy disorder of PTAA. Additionally, FCNO₂-incorporated PTAA also reduces the free energy barrier for nucleation, contributing to obtaining a pinhole-free bottom surface of the perovskite layer. Consequently, the best perovskite solar module (PSM) achieves a power conversion efficiency of 20.6% (certified 20.1%, 57.3 cm²), which is record-high for inverted PSMs with an active area exceeding 50 cm². Moreover, the resulting PSM can maintain 94% of its original efficiency after continuous operation for 1500 h under 1-sun illumination. Our results demonstrate that the reduction of energy disorder in organic charge transport layers through the co-assembling strategic application of highly electrophilic molecules is an effective approach to enhancing the performance of PSMs.