Efficient Organic Solar Cells Fabricated with a High‐Boiling Solvent Via Morphology Modulation Using a Small Molecule Guest Donor

Abstract It is necessary to employ high‐boiling solvents for the fabrication of large‐area organic solar cells (OSCs). However, controlling the morphology to achieve suitable phase separation for high efficiency is challenging when high‐boiling solvents are used. In this study, HD‐1, a small molecular donor is introduced, into the PM6:BO‐4Cl blend as a morphology‐modulating agent. This addition optimizes the phase separation and enhances charge transport in the ternary blend processed in chlorobenzene (CB) solvent. The optimized active layer demonstrates improved charge dissociation and transport capabilities while effectively suppressing charge recombination. Small‐area OSCs processed from the CB solution achieves an improved power conversion efficiency (PCE), increasing from 18.84% to 19.42%. Furthermore, the device demonstrated good tolerance of active layer thickness, with a 300‐nm‐thick film achieving a PCE exceeding 17%. Notably, a blade‐coated module with an active area of 13.5 cm 2 , fabricated in air using CB, achieves a PCE of 16.48%, showing excellent application potential. This study presents a straightforward and effective approach to optimizing active layer morphology and enhancing the PCE of OSCs fabricate using a high‐boiling solvent, highlighting its potential for large‐scale production and practical applications.