Asymmetrically Substituted Phthalocyanines as Dopant-Free Hole Selective Layers for Reliability in Perovskite Solar Cells

Dopant-free metal phthalocyanines are viable alternatives to the classical Spiro-OMeTAD in perovskite solar cells (PSCs), due to their appealing optoelectrical properties and chemical stability. However, low carrier concentration, transportability, and narrow bandgap limit their application. Here, we designed and investigated six innovative asymmetrically substituted metal phthalocyanines (MPcs, M = Zn or Cu), and established the correlation between electronic structure, charge carrier transfer parameter, and core metal/substitutions in MPcs by transient absorbance spectroscopy and electronic paramagnetic resonance. We probed the charge transport properties of ZnPcs including carrier lifetime, diffusion coefficient, and diffusion length by transient absorbance spectroscopy. We noted, ZnPcAE presents a longer diffusion length (1.94 nm) than of control ZnPcTB4 (0.80 nm), which is advantageous for reducing charge recombination and gave higher power conversion efficiency in the fabricated PSCs. Importantly, the devices with MPcs yielded improved stability under multi-stress conditions. Our work provides a molecular guideline for designing MPcs and their application as dopant-free hole-transporting materials for perovskite solar cells fabrication.