The Fabrication of Gradient Cd‐Doped ZnO Electron Transport Layers for High Efficiency Large‐Area Organic Solar Modules

Organic solar cells (OSCs) with an inverted device architecture exhibit superior long‐term stability, which is essential for the commercialization of large‐area organic solar modules. However, the commonly used zinc oxide (ZnO) electron transport layer (ETL) suffers from intrinsic defects, energy level mismatch with the active layer, and challenges in achieving uniform and fully covered films during the fabrication of large‐area modules. In this paper, we develop a gradient Cd‐doped ZnO (G‐CZOs) ETL with a gradient Cd‐doping profile (from bottom to top: 2%, 3%, and 5% Cd‐doping cocentrations), which significantly reduces defect states and establishes a gradient energy‐level alignment from the electrode to the active layer. The power conversion efficiencies (PCEs) of PM6:L8‐BO OSCs increase from 17.2% with ZnO ETL to 18.7% with G‐CZOs ETL due to their enhanced charge extraction and suppressed charge recombination, further improving to 18.9% in PM6:L8‐BO:BTP‐eC9 ternary devices. Moreover, 5 × 5 cm 2 large‐area modules (with an effective area of 12 cm 2 ) based on the G‐CZOs ETL achieve a PCE of 15.8%, outperforming the 14.0% obtained for ZnO‐based modules, while also exhibiting excellent stability. The development of the multi‐layer gradient Cd‐doped ZnO ETL presents a novel technological approach for developing highly efficient and stable large‐area organic solar modules.