Organic solar cells (OSCs) technology is regarded as one of the most promising sustainable and green energy sources for their promise as environmentally friendly and easily printable devices. [1-6] In recent years, bulk-heterojunction (BHJ) OSCs Organic solar cells (OSCs) have made rapid progress in terms of their development as a sustainable energy source. However, record-breaking devices have not shown compatibility with large-scale production via solution processing in particular due to the use of halogenated environment-threatening solvents. Here, slot-die fabrication with processing involving hydrocarbon-based solvents is used to realize highly efficient and environmentally friendly OSCs. Highly compatible slot-die coating with roll-to-roll processing using halogenated (chlorobenzene (CB)) and hydrocarbon solvents (1,2,4-trimethylbenzene (TMB) and ortho-xylene (o-XY)) is used to fabricate photo active films. Controlled solution and substrate temperatures enable similar aggregation states in the solution and similar kinetics processes during film formation. The optimized blend film nanostructures for different solvents in the highly efficient PM6:Y6 blend is adopted to show a similar morphology, which results in device efficiencies of 15.2%, 15.4%, and 15.6% for CB, TMB, and o-XY solvents. This approach is successfully extended to other donor-acceptor combinations to demonstrate the excellent universality of this method. The results combine a method to optimize the aggregation state and film formation kinetics with the fabrication of OSCs with environmentally friendly solvents by slot-die coating, which is a critical finding for the future development of OSCs in terms of their scalable production and high-performance.

As a prototype tool for slot‐die coating, blade‐coating exhibits excellent compatibility with large‐area roll‐to‐roll coating. A ternary organic solar cell based on PBDB‐T:PTB7‐Th:FOIC blends is fabricated by blade‐coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment. It is demonstrated that blade‐coating can enhance crystallization of these three materials, but the degree of induction is different (FOIC > PBDB‐T > PTB7‐Th). Thus, the blade‐coated PBDB‐T:FOIC device presents much higher electron mobility than hole mobility due to the very high crystallinity of FOIC. Upon the addition of PTB7‐Th into the blade‐coated PBDB‐T:FOIC blends, the crystallinity of FOIC decreases together with the corresponding electron mobility, due to the better miscibility between PTB7‐Th and FOIC. The ternary strategy not only maintains the well‐matched crystallinity and mobilities, but also increases the photocurrent with complementary light absorption as well as the Förster resonant energy transfer. Furthermore, small domains with homogeneously distributed nanofibers are observed in favor of the exciton dissociation and charge transport. This combination of blade‐coating and ternary strategies exhibits excellent synergistic effect in optimizing morphology, showing great potential in the large‐area fabrication of highly efficient organic solar cells.

Due to the attraction of optimizing the electronic structure beyond chemical synthesis, molecular doping has recently aroused wide interest in the field of organic solar cells. However, the selection of limited dopants confines its successful application. Inspired by the Lewis base characteristics of the photovoltaic materials, the Lewis acid as novel dopant is introduced in organic solar cells. In both fullerene and nonfullerene based blends, Lewis acid doping leads to increased photovoltaic performance. Detailed experiments reveal that Lewis acid doping has a synergistic effect on modifying the polymer's electronic properties and the acceptor's nanostructure even at low doping concentration, and these are simultaneously responsible for the device improvements. Based on the mechanism studies, it is proposed that the Lewis acid‐doped polymers anions produce induced dipole on the acceptor, this increases the intermolecular interaction and facilitates the morphology optimization. It is believed that the synergistic effect by Lewis acid doping greatly expands the application of doped organic solar cells, in concert with other existing methods to yield higher efficiency values.

Sequential deposition has great potential to achieve high performance in organic solar cells due to the well-controlled vertical phase separation. In this work, double bulk heterojunction organic solar cells were fabricated by sequential-blade cast in ambient condition, which is higher than the corresponding binary devices. Probed by the in-situ grazing incidence X-ray diffraction and in-situ UV-vis absorption measurements, the seq-blade system exhibited a different tendency from each of binary devices during the film formation process. Due to the extensive aggregation of FOIC, the binary PBDB-T:FOIC film displayed a strong and large phase separation, resulting in the low current density (Jsc) and unsatisfactory PCE.