Boosting inverted perovskite solar cell performance by using 9,9-bis(4-diphenylaminophenyl)fluorene functionalized with triphenylamine as a dopant-free hole transporting material

In this study, two newly developed small molecules based on 9,9-bis(4-diphenylaminophenyl)fluorene functionalized with triphenylamine moieties, namely TPA-2,7-FLTPA-TPA and TPA-3,6-FLTPA-TPA , are designed, synthesized and characterized. The electrochemical, optical and thermal properties of both materials are investigated using various techniques. Afterwards, these materials are employed as dopant-free hole transporting materials (HTMs) in planar inverted perovskite solar cell devices with the aim of determining the device performance and studying their stability in comparison with reference N 4 , N 4 , N 4 ′′, N 4 ′′-tetra([1,10-biphenyl]-4-yl)-[1,1′:4′,1′′-terphenyl]-4,4′′-diamine (TaTm)-based devices. Under 1 sun conditions, TPA-3,6-FLTPA-TPA -based devices achieve a power conversion efficiency (PCE) of 13.9% whereas TPA-2,7-FLTPA-TPA -based devices exhibit the highest PCE of 17.1% mainly due to an improvement in the fill factor (FF). Meanwhile, the devices prepared using TaTm as the reference HTM exhibit an overall efficiency of 15.9%. In addition to the higher efficiency, our newly developed HTM TPA-2,7-FLTPA-TPA -based devices demonstrate good stability which is comparable to those with TaTm under similar aging test conditions. New small molecules based on 9,9-bis(4-diphenylaminophenyl)fluorene functionalized with triphenylamine moieties are developed for use as dopant-free hole transporting materials (HTMs) in planar inverted perovskite solar cells. Power conversion efficiencies (PCE) as high as 17.1% are obtained with good stability.