Performance Improvement in Low-Temperature-Processed Perovskite Solar Cells by Molecular Engineering of Porphyrin-Based Hole Transport Materials

Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (P_Zn)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the P_Zn core for low-temperature perovskite solar cells (L-PSCs). The fluorinated P_Zn-HTLs (P_Zn-2FTPA and P_Zn-3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (P_Zn-TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using P_Zn-2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the PSCs using porphyrin-based HTLs.