Improved performance and air stability of perovskite solar cells based on low-cost organic hole-transporting material X60 by incorporating its dicationic salt

The development of an efficient, stable, and low-cost hole-transporting material (HTM) is of great significance for perovskite solar cells (PSCs) from future commercialization point of view. Herein, we specifically synthesize a dicationic salt of X60 termed X60(TFSI)2, and adopt it as an effective and stable "doping" agent to replace the previously used lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) for the low-cost organic HTM X60 in PSCs. The incorporation of this dicationic salt significantly increases the hole conductivity of X60 by two orders of magnitude from 10-6 to 10-4 S cm-1. The dramatic enhancement of the conductivity leads to an impressive power conversion efficiency (PCE) of 19.0% measured at 1 sun illumination (100 mW cm-2, AM 1.5 G), which is comparable to that of the device doped with LiTFSI (19.3%) under an identical condition. More strikingly, by replacing LiTFSI, the PSC devices incorporating X60(TFSI)2 also show an excellent long-term durability under ambient atmosphere for 30 days, mainly due to the hydrophobic nature of the X60(TFSI)2 doped HTM layer,which can effectively prevent the moisture destroying the perovskite layer. The present work paves the way for the development of highly efficient, stable, and low-cost HTM for potential commercialization of PSCs.