Dibenzo[b,d]thiophene-Cored Hole-Transport Material with Passivation Effect Enabling the High-Efficiency Planar p-i-n Perovskite Solar Cells with 83% Fill Factor

N-2,N-2,N-8,N-8-tetrakis(4-(methylthio)phenyl)dibenzo[b,d]thiophene-2,8-diamine (DBTMT) is synthesized from three commercial monomers for application as a promising dopant-free hole-transport material (HTM) in perovskite solar cells (pero-SCs). The intrinsic properties (optical properties and electronic energy levels) of DBTMT are investigated, proving that DBTMT is a suitable HTM for the planar p-i-n pero-SCs. The champion power conversion efficiency (PCE) of the optimized pero-SCs (with structure as ITO/pristine DBTMT/MAPbI(3)/C-60/BCP/Ag) reaches 21.12% with a fill factor (FF) of 83.25%, which is among the highest PCEs and FFs reported for planar p-i-n pero-SCs based on dopant-free HTMs. The Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy spectra of MAPbI(3) and DBTMT-MAPbI(3) films demonstrate that there is an interaction between DBTMT and MAPbI(3) at the interface through the sulfur atoms in DBTMT to passivate the defects, which is corresponding to the higher FF and PCE of the corresponding device.