Effects of Heteroatom and Extending the Conjugation on Linear Hole-Transporting Materials for Perovskite Solar Cells

The investigation of high-performance molecular hole-transporting materials (HTMs) plays an irreplaceable role in the improvement of perovskite solar cells (PSCs). Herein, four thiophene-arylamine linear HTMs with different π-bridges have been designed and prepared. The effects of the heteroatom and extending the conjugation by double bonds on molecular optical, electrochemical, hydrophobic, film-forming, and photovoltaic performance in PSCs are investigated. The molecules with double bonds demonstrate significantly better planarity and more efficient intramolecular charge transfer, leading to higher hole mobility and better hole extraction ability. Moreover, it is noted that the molecules with the oxygen-based bridge (3,4-ethylenedioxythiophene) exhibit more planar structures compared with sulfur-based ones (3,4-ethylenedithiothiophene) whether they contain double bonds or not. When used in PSCs, the devices based on more planar molecules containing extending double bond conjugation and the oxygen-based bridge obtain higher efficiency and improved stability. Moreover, the 3,4-ethylenedioxythiophene-bridged molecule with double bonds even shows an efficiency over 20%, which is even slightly higher than the conventional spiro-OMeTAD under the same conditions.