Fluorinated dopant-free hole-transporting material for efficient and stable perovskite solar cells with carbon cathode

In this work, we develop a novel fluorinated small molecule BDT2FMeDPA, and further apply it as a dopant-free hole-transport material (HTM) for low-cost, efficient and stable perovskite solar cells (PSCs) with the vacuum free carbon cathode. BDT2FMeDPA can be simply synthesized from commercial raw materials with a low production cost. With the introduction of fluorine atoms in BDT2FMeDPA, the hole mobility and conductivity are significantly enhanced with an appropriate energy level alignment as compare with its non-fluorinated analogue (BDT0FMeDPA). The optimized PSC devices with pristine BDT2FMeDPA afford a decent power conversion efficiency of 14.5%, which is considerably higher than the devices using its non-fluorinated analogue (11.3%) under equivalent conditions. Moreover, the PSCs devices incorporating BDT2FMeDPA also show good long-term air stability, maintaining over 90% of its initial efficiency after 30 days under ambient atmosphere, due largely to its hydrophobic characteristic and the carbon cathode. The present work not only emphasizes that the performance of HTM can be effectively tuned through the introduction of fluorine atoms, but also provides insights into future design of dopant-free HTM for low-cost, stable and highly efficient PSCs.