Unified Molecular Orientation in Naphthalimide‐Based Cathode Interlayers Enables Efficient Large‐Area Organic Photovoltaic Modules

ABSTRACT The film‐forming uniformity and charge extraction capability of cathode interlayers (CILs) are critical to the performance of organic photovoltaic (OPV) modules, yet CILs scalable to module fabrication remain underexplored. Herein, we design four naphthalimide‐based CILs by independently varying the π ‐bridges (furan or thiophene) and the terminal groups (amine or imidazole), denoted as F‐NN, T‐NN, F‐M, and T‐M, via a facile two‐step synthetic procedure free of column purification. We find that two imidazole‐terminated naphthalimides (F‐M and T‐M) allow more favorable cathode work function tuning and adopt unified molecular orientations, which collectively improve charge extraction and film‐forming uniformity of CILs. Consequently, small‐area OPVs based on F‐M and T‐M deliver power conversion efficiencies (PCEs) of 19.35% and 19.49%, respectively. More importantly, the same molecular alignments in CILs mitigate defect formation during scale‐up, resulting prominent PCEs of 16.70% and 16.26% for the F‐M and T‐M based modules with an aperture area of 20.25 cm 2 , respectively, outperforming the amine‐terminated naphthalimides (F‐NN and T‐NN) based counterparts. These results highlight orientation control, via imidazole terminals, as a feasible route to high‐efficiency OPV modules and offer guidance for future CIL design.