Dopant-Free Hole-Transporting Layer Based on Isomer-Pure Tetra-Butyl-Substituted Zinc(II) Phthalocyanine for Planar Perovskite Solar Cells

Herein, the important role of the isomer purity of hole-transporting materials (HTMs) in achieving high-performance perovskite solar cells (PSCs) is highlighted. The isomer-pure 2,9,16,24-tetra-n-butyl-Zn(II) phthalocyanine (RE-ZnBu4Pc) is directly synthesized through a ring expansion method, without any further purification. The ground-state absorption, fluorescence and thermal properties of RE-ZnBu4Pc and the isomer mixture ZnBu4Pc, along with their hole mobilities and film morphologies are investigated, proving that RE-ZnBu4Pc can be the more efficient HTM. The devices based on RE-ZnBu4Pc, as dopant-free HTMs, achieve a higher average power conversion efficiency (PCE of 11.49% +/- 0.67%) and more stability at 25 degrees C and under 75% relative humidity than that of isomer mixture ZnBu4Pc (PCE of 9.51% +/- 1.15%). RE-ZnBu4Pc-based PSCs also show better reproducibility in the fabrication process. This study demonstrates that better device performance can be expected for PSCs with isomer-pure HTM materials.