Side chain engineering and film uniformity: two key parameters for the rational design of dopant-free polymeric hole transport materials for efficient and stable perovskite solar cells

Abstract

Herein, we introduce a series of new (X–DADAD)n-type conjugated polymers comprised of benzo[1,2-b:4,5-b′]dithiophene (X), benzo[c] [1,2,5]thiadiazole (acceptor, A), and thiophene (donor, D) units as highly promising hole transport materials for perovskite solar cells (PSCs). The rational engineering of the backbone structure and the side chains enabled high power conversion efficiencies of up to 20% in n-i-p perovskite solar cells in combination with impressive operational stability: the devices preserved initial performance after >2500 h of continuous illumination at open-circuit conditions. The origins of the observed long-term perovskite solar cells stability enabled by the newly designed polymeric hole transport materials have been revealed through the use of infrared scattering-type scanning near-field optical microscopy and further elucidated by density functional theory calculations. The presented findings point to novel strategies of designing advanced charge transport materials to simultaneously endow the PSCs with high performance and durability.