Nonhalogenated Dual‐Slot‐Die Processing Enables High‐Efficiency Organic Solar Cells

Abstract Organic solar cells (OSCs) are promising candidates for next‐generation photovoltaic technologies, with their power conversion efficiencies (PCEs) reaching 19%. However, the typically used spin‐coating method, toxic halogenated processing solvents, and the conventional bulk‐heterojunction (BHJ), which causes excessive charge recombination, hamper the commercialization and further efficiency promotion of OSCs. Here, a simple but effective dual‐slot‐die sequential processing (DSDS) strategy is proposed to address the above issues by achieving a continuous solution supply, avoiding the solubility limit of the nonhalogen solvents, and creating a graded‐BHJ morphology. As a result, an excellent PCE of 17.07% is obtained with the device processed with o‐xylene in an open‐air environment with no post‐treatment required, while a PCE of over 14% is preserved in a wide range of active‐layer thickness. The unique film‐formation mechanism is further identified during the DSDS processing, which suggests the formation of the graded‐BHJ morphology by the mutual diffusion between the donor and acceptor and the subsequent progressive aggregation. The graded‐BHJ structure leads to improved charge transport, inhibited charge recombination, and thus an excellent PCE. Therefore, the newly developed DSDS approach can effectively contribute to the realm of high‐efficiency and eco‐friendly OSCs, which can also possibly be generalized to other organic photoelectric devices.