Vertical phase separation and morphology optimization of layer-by-layer non-fullerene organic solar cells

The development of high-performance non-fullerene acceptors with extended exciton diffusion lengths has positioned the sequential layer-by-layer (LBL) solution processing technique as a promising approach for fabricating high-performance and large-area organic solar cells (OSCs). This method allows for the independent dissolution and deposition of donor and acceptor materials, enabling precise morphology control. In this review, we provide a comprehensive overview of the LBL processing technique, focusing on the morphology of the active layer. The swelling-intercalation phase-separation (SIPS) model is introduced as the mainstream theory of morphology evolution, with a detailed discussion on vertical phase separation. We summarize recent strategies for morphology optimization. Additionally, we review the progress in LBL-based large-area device and module fabrication, as well as green processing approaches. Finally, we highlight current challenges and future prospects, paving the way for the commercialization of LBL-processed OSCs.