Reducing steric hindrance around electronegative atom in polymer simultaneously enhanced efficiency and stability of organic solar cells

Uncovering the underlying rules that determine efficiency and device stability of polymer donors is crucially important for future rational design of new materials. By reducing bulkiness of alkyl chain in NTI, we synthesized polymer donor PNTB-HD. The PNTB-HD:N3 based photovoltaic device exhibits the highest PCE of 18.15% that is among the best efficiency in binary devices. More encouragingly, it demonstrates much better device thermal stability than PNTB-2T and the most widely used polymer PM6. Compared with PNTB-2T, PNTB-HD has more condensed packing and stronger tendency to preassembly in chloroform solution that is reason for simultaneously enhancement of efficiency and thermal stability. Single crystal data further revealed reducing alkyl chain bulkiness in NTI could significantly enhance short interaction of C=O…H-C between adjacent molecules that provide useful information to understand the physical property variation of two polymers. This study revealed reducing steric hindrance around electronegative atom is an effective strategy for designing high-performance polymers donors.