Diarylfluorene-based nano-molecules as dopant-free hole-transporting materials without post-treatment process for flexible p-i-n type perovskite solar cells

A series of diarylfluorene-based nano-molecules were applied as hole transporting layers (HTLs) without any dopants and post-treatment process in the preparation of p-i-n type perovskite solar cells (PVSC). Smooth, amorphous and hydrophobic films could be facilely deposited by spin coating, which was beneficial for enhancing the device performance and constructing flexible electronic devices in large scale. Compared to the referenced device that adopted poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) as the HTLs, these novel materials were favorable for the growth of perovskite film with larger grain size and less grain boundaries. The hole extraction at the HTLs/perovskite film interface and the hole transport in HTLs were also more efficient under the conditions of taking the diarylfluorene-based nano-molecules as HTLs. Through further optimization, stabilized preliminary high power conversion efficiency (PCE) of 13.85% was achieved, much higher than the PCE of 11.90% achieved using PEDOT:PSS. Finally, flexible devices adopted poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) as substrate was also fabricated through the same fabrication procedure, and a maximum PCE 9% was achieved. We speculate that these diarylfluorene-based nano-molecules have promising application in next generation solar cells.