Bacteriochlorin aggregates as dopant-free hole-transporting materials for perovskite solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted great interests not only of academic field but also of industrial world toward practical applications in the last decade due to their extremely low production cost and excellent photo-physical properties. Hole-transporting layer (HTL) as an integral component of PSC plays an important role in elevating its performance. In this work, five bacteriochlorophyll- a derivatives characterized by different C17-propionate residue were prepared and their J- type aggregates were investigated as HTLs of PSCs. It was confirmed that the nature of the introduced C17-propionate side chains have negligible effects on the electrochemical properties of main dye unit, such as the electronic absorption spectra and energy levels. However, the different lipophilicity , hydrophilicity , or hydrophobicity of chain characters affect the solubility of each dye component, resulting in diverse surface morphologies of their aggregate films as revealed by AFM observations. Furthermore, the five solid films prepared by spin-coating method showed discrepant charge extraction and transport abilities as HTLs, which were supported by both photo luminescence spectra and electrochemical impedance spectroscopy measurement results and were concluded to be the fundamental reason of the different PSC performance.