Organic Photovoltaics (OPVs) have received widespread attention and research, owing to their unique advantages like inexpensive, light weight, flexible, processable and less environmental pollution. In the past decades, due to the efforts made in device engineering and material replacement, bulk heterojunction (BHJ) OPVs has developed rapidly with power conversion efficiency (PCE) exceeding 20 % in recently developed non-fullerene small-molecules acceptors (NFAs) to replace fullerene-counterpart¹.

To further improve the performance of NFA-OPV, a ternary strategy was evolved by adding a proper third component to the binary system. High potential PCEs are offered by ternary system where either the third component acts as an additional donor or additional acceptor that serves to extend the range of absorption and can also tune material properties. Interestingly, the incorporation of the third counterpart that serves to extend the range of absorption and can also tune material properties. It can regulate the accumulation and orientation of the molecule, as well as the phase separation of donor and acceptor, providing high crystallinity and ordered molecular stacking that can improve the charge transport and inhibit the bimolecular recombination through well optimized phase separation^2,3.

However, most research on ternary strategies is based on the bulk hetero junction (BHJ) system. This makes it difficult to control other important morphological parameters, such as molecular orientation and domain purity as it further complicates the morphological regulation. Accordingly, to tailor vertical phase distribution efficiently, the Layer-by-Layer (LBL) deposition approach of the layers is considered as a promising alternative to the BHJ. The sequential deposition method allows the carefully controlled arrangement and orientation of the organic molecules, leading to improved photovoltaic performance. It avoids the difficulty of controlling the bulk morphology through forming a proper vertical phase separation that can be controlled, which is efficient for the charge transportation and collection at the corresponding electrodes. Furthermore, p–i–n-like bilayer structure enables easier exciton dissociation at the D/A interface and can reduce charge carrier recombination loss^4,5.

Hence, in this piece of work, I have developed a novel OPV structure, introducing a perovskite quantum dots (PQDs) interlayer sandwiched between the organic semiconductor donor and the NFA layers using LBL deposition approach, resulting in enhancement in the performance of  QDs based OPV devices by 11% ( from PCE of 16.6 % for the pristine Binary OPV to PCE = 18.8%  for the QDs-based Ternary OPV) along with 99 % performance retention after 3 months of storage compared to only 30% for the bilayer devices without PQDs. This unique structure allows for the LBL preferred vertical phase separation and well-controlled D/A interface film morphology, exhibiting efficient transport and extraction properties. Moreover, the incorporation of PQDs to create alloy structure with the NFA was beneficial for reducing bimolecular and trap-assisted recombination at the interface, improving exciton separation, and charge transfer, resulting in the higher, V_OC, J_SC, and FF of the PQDs based device. Finally, our findings evidence that introducing the PQDs as a third component in the interface between the donor and the NFA via LBL deposition approach is an effective strategy to improve the interfacial microstructure of the active layers, resulting in high-performance OPV devices.