Effects of core moiety and substituted positions in phenothiazine-based hole transporting materials towards high thermal stability and good hole mobility

Abstract

Two hole transporting materials (HTMs), SFX-PT1 and SFX-PT2, were designed and synthesized by combing a spiro[fluorene-9, 9′-xanthene] (SFX) core with tetra- phenothiazine substituted at the 2,2′,7,7′- and 2,3′,6,′7-positions, respectively. As comparison, a HTM with tetra-phenothiazine substituted at the 2,2′,7,7′-positions of a 9, 9′-spirobifluorene core (Spiro-PT) was also synthesized. Their photophysical and electrochemical properties, thermal stability and hole mobility were investigated. It was demonstrated that SFX-centered HTMs exhibited superior Stokes shift, thermal stability and hole mobility than those of Spiro-PT. Combining with the substituted positions modification, SFX-PT1 has the largest Stokes shift of 197 nm, the highest decomposition temperature of 435 °C and hole mobility of 2.08 × 10−3 cm2V−1S−1. Moreover, the energy levels of the HTMs were matched very well with that of CH3NH3PbI3. Our results indicated that SFX-centered, phenothiazole substituted HTMs might be potential candidates for efficient perovskite solar cells.