EH44 is a Li+ free, hydrophobic hole transporting material (HTM). It eliminates degradation due to Li+ migration, supresses degradation due to moisture absorption and thus showed promise for achieving long-term stability in fabricated perovskite solar cells.
Using EH44 as HTM in a device configuration of: SnO2/PAL/EH44/MoOx /Al, not only generated high power conversion efficiency (PCE) comparable to the record PCE by using the state-of-the-art-HTM Spiro-OMeTAD, but also most importantly showed greatly improved device stability: even under the combined stresses of light (including ultraviolet light), oxygen and moisture, perovskite solar cells using EH44 as hole transporting layer were shown to retain 94% of their peak efficiency despite 1,000 hours of continuous unencapsulated operation in ambient air conditions (relative humidity of 10-20%). When stability tests were conducted in an inert atmosphere, degradation of only ～2% over the course of 1,500 hours of continuous operation was observed.
Note that in the above mentioned result, silver bis(trifluoromethanesulfonyl)imide (product 668001) was used to oxidize EH44 and yield EH44+TFSI?.EH44+TFSI? was then blended with neat EH44 at various ratios to control the conductivity (and optical transparency if desired) and optimize the device performance. The impressive power conversion efficiency (PCE) of 18.5% was achieved for a perovskite solar cell using EH44 layers of ～60 nm thickness doped with 14wt% EH44+TFSI? and 25 mg/ml 4-tert-butylpyridine (product 142379), which is comparable to device performance using spiro-OMeTAD (19%) as the HTM.
