All-rounder low-cost dopant-free D-A-D hole-transporting materials for efficient indoor and outdoor performance of perovskite solar cells

A novel biphenyl fumaronitrile as an acceptor and triphenylamine as donor conjugated building blocks are used for the first time to successfully synthesize donor¿acceptor¿donor molecule (D-A-D) 2,3-bis(4'-(bis(4-methoxyphenyl)amino)-[1,1'-biphenyl]-4-yl)fumaronitrile (TPA-BPFN-TPA). The new TPA-BPFN-TPA with low-lying HOMO is used as a dopant-free hole-transporting material (HTM) in mesoporous perovskite solar cells. The performance of the solar cells using this new HTM is compared with the traditional 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamino)- 9,9'-spirobifluorene (Spiro-OMeTAD) HTM based devices for outdoor and indoor performance evaluation. Under 1 sun illumination, dopant-free TPA-BPFN-TPA HTM based devices exhibit a power conversion efficiency (PCE) of 18.4%, which is the record efficiency to date among D-A-D molecular design based dopant-free HTMs. Moreover, the stability of unencapsulated TPA-BPFN-TPA-based devices shows improvement over Spiro-OMeTAD-based devices in harsh relative humidity condition of 70%. Another exciting feature of the newly developed HTM is that the TPA-BPFN-TPA-based devices exhibit improved PCE of 30% and 20.1% at 1000 lux and 200 lux illuminations, respectively. This new finding provides a solution to fabricate low indoor (low light) and outdoor (1 sun) perovskite solar cell devices with high efficiency for cutting-edge energy harvesting technology.