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.