Enhanced Self‐Assembly of Hole Transporters via Surface Energy Modulation Enables Co‐Deposited Organic Solar Cells With 20% Efficiency

ABSTRACT Co‐depositing hole transporters with light‐absorbing active layers is a promising approach for simplifying the fabrication of organic solar cells (OSCs). However, this simplified method currently yields significantly lower performance compared to the traditional sequential deposition method. Our work reveals that a major reason for this is the insufficient adsorption of self‐assembling hole‐transporting materials onto the transparent conductive oxide (TCO) substrate, which degrades deposition uniformity and charge transport. To address this, we develop a new strategy that incorporates poly(styrene sulfonic acid) (PSS), a material characterized by high hydrophilicity and surface energy. The addition of PSS effectively promotes the self‐assembly of the hole‐transporting materials toward the TCO during co‐deposition. This reduces un‐adsorbed areas and suppresses nonradiative recombination. Consequently, our co‐deposited OSCs achieved an efficiency of 20.0%, which is the highest reported efficiency for this type of device to date. Furthermore, an organic solar module based on this strategy also achieved a high efficiency of 17.0% with an aperture area of 12.0 cm 2 .