Morphology control in laboratory and industry setting remains as a major challenge for organic solar cells (OSCs) due to the difference in film-drying kinetics between spin coating and the printing process. A two-step sequential deposition method is developed to control the active layer morphology. A conjugated polymer that self-assembles into a well-defined fibril structure is used as the first layer, and then a non-fullerene acceptor is introduced into the fibril mesh as the second layer to form an optimal morphology. A benefit of the combined fibril network morphology and non-fullerene acceptor properties was that a high efficiency of 16.5% (certified as 16.1%) was achieved. The preformed fibril network layer and the sequentially deposited non-fullerene acceptor form a robust morphology that is insensitive to the polymer batches, solving a notorious issue in OSCs. Such progress demonstrates that the utilization of polymer fibril networks in a sequential deposition process is a promising approach towards the fabrication of high-efficiency OSCs.

In non-fullerene organic solar cells, the long-range structure ordering induced by end-group π–π stacking of fused-ring non-fullerene acceptors is considered as the critical factor in realizing efficient charge transport and high power conversion efficiency. Here, we demonstrate that side-chain engineering of non-fullerene acceptors could drive the fused-ring backbone assembly from a π–π stacking mode to an intermixed packing mode, and to a non-stacking mode to refine its solid-state properties. Different from the above-mentioned understanding, we find that close atom contacts in a non-stacking mode can form efficient charge transport pathway through close side atom interactions. The intermixed solid-state packing motif in active layers could enable organic solar cells with superior efficiency and reduced non-radiative recombination loss compared with devices based on molecules with the classic end-group π–π stacking mode. Our observations open a new avenue in material design that endows better photovoltaic performance.

The development of semitransparent organic solar cells (ST-OSCs) stands for a significant step toward the commercialization of OSCs. However, the trade-off between power conversion efficiency (PCE) and average visible transmittance (AVT) restricts further improvements of ST-OSCs. Herein, we demonstrated that a fibril network strategy can enable ST-OSCs with high PCE and AVT simultaneously. In details, a wide-bandgap polymer PBT1-C-2Cl which can self-assemble into fibril nanostructure has been used as the donor and a near-infrared small molecule Y6 has been adopted as the acceptor. It was found that a tiny amount of PBT1-C-2Cl in the blend can form a high speed pathway for hole transport due to the well distributed fibril nanostructure, which increases the transmittance in the visible region. Meanwhile, the acceptor Y6 guarantees sufficient light absorption. Using this strategy, the optimized ST-OSCs yielded a high PCE of 9.1% with an AVT of over 40% and significant LUE of 3.65% at D:A ratio of 0.25:1. This work demonstrates a simple and effective approach to realizing high PCE and AVT of ST-OSCs simultaneously.