Facile and Stable Fluorene Based Organic Hole Transporting Materials for Efficient Perovskite Solar Cells

Although the small molecule hole-transporting materials (HTMs) pop up with an efficiency of over 25%, long-term stability still needs to be improved for the commercialization of perovskite solar cells. In the current work, we designed two fluorine-dithiophene (FDT)-based small molecule HTMs (F2DT and FDT-DMP), and comparative studies of HTMs were performed for stable donor-acceptor-donor (D-A-D) perovskite solar cells. Notably, the introduction of fluorene-terminated groups on FDT resulted in fine-tuned energy levels and better thermal stability with a high glass transition temperature (Tg∼157 °C), which follow-on enhanced perovskite device performance of F2DT. The hydrophobic nature of the F2DT compound truly favored the formation of uniform and dense perovskite films that further improved the stability of the devices. The comparison studies revealed that F2DT displayed higher power conversion efficiency (PCE) of 18% than FDT-DMP (PCE of 12.3%). The resultant F2DT device displays better stability than the device with FDT-DMP, maintaining almost 80% of its initial performance for more than 300 h.