Organic solar cells (OSCs), characterized by their lightweight, flexibility, solution-processability for large-area fabrication, and low cost, exhibit significant complementary advantages to silicon-based photovoltaics, positioning them as a cutting-edge research frontier in clean energy. Among emerging architectures, small-molecule donor/polymer acceptor (SDPA)-based OSCs have attracted considerable attention due to their unique active layer stability, particularly their ability to maintain optimized phase-separated morphology under high-temperature conditions (>85 °C), offering potential to overcome the stability bottleneck in organic photovoltaic industrialization. However, the current record power conversion efficiency (PCE) of SDPA-OSCs remains at 12.1 %, significantly lagging behind mainstream bulk heterojunction systems (PCE >20 %). To advance the efficiency of SDPA-OSCs, extensive efforts have been devoted to optimizing materials, device engineering, and processing techniques. This review systematically summarizes recent progress in SDPA-OSCs from the perspectives of device architecture and active layer processing. Key focus areas include the impact of device structure engineering (conventional vs. inverted configurations) and active layer fabrication strategies (bulk heterojunction solution-coating and layer-by-layer deposition techniques) on charge carrier transport and device performance. By establishing robust “material structure–morphology–device performance” correlations, this work provides critical insights and technical references for developing high-efficiency SDPA-OSCs. Furthermore, future research directions and challenges in material innovation, morphology control, and scalable manufacturing are discussed to guide the advancement of SDPA-based organic photovoltaics.

Small-molecule donor:polymer acceptor (SMD:PA) organic solar cells have garnered attention due to their excellent active layer stability, yet their efficiency remains significantly lower than other OSC types. This study addresses the challenge of morphology control in SMD:PA systems via a layer-by-layer (LBL) process to optimize the donor–acceptor interpenetrating network. Using small-molecule donor B1 and polymer acceptor PY-IT with chloroform as a universal solvent, we systematically investigated the impact of LBL processing on the active layer morphology and device performance. The inverted LBL device (ITO/ZnO/PY-IT/B1/MoO3/Ag) achieved a power conversion efficiency of 8.6%, significantly outperforming the bulk heterojunction devices (inverted 2.91% and normal 6.11%) and previously reported LBL SMD:PA cells (1.12%). Static and femtosecond transient absorption spectra, time-resolved photoluminescence, and grazing incidence X-ray diffraction analyses revealed that the LBL and nonorthogonal solvent strategy facilitated effective B1 infiltration into the PY-IT layer, forming an optimized active layer with refined phase separation and improved donor/acceptor interfaces, thus resulting in enhanced exciton dissociation and charge transport while reducing recombination losses. This work validates the feasibility of LBL processing for high-efficiency SMD:PA OSCs, offering a novel strategy to overcome the efficiency limitations of this class of OSCs.