Tetra-alkyl-substituted copper (II) phthalocyanines as dopant-free hole-transport layers for planar perovskite solar cells with enhanced open circuit voltage and stability

The tetra-alkyl substitution increased the π-π interactions for thin-film fabrication and led to higher carrier mobility compared with that of pristine copper(II) phthalocyanine, giving the highest power conversion efficiency of 11.9% for the CuMePc-based perovskite solar cell. Moreover, the introduction of tetra-alkyl groups resulted in a more hydrophobic surface and more condensed thin-film structure, leading to the best long-term device stability of the CuEtPc-based device, with a power conversion efficiency of 11.7%.391