Fluorination Triggered New Small Molecule Donor Materials for Efficient As‐Cast Organic Solar Cells

Solution‐processable small molecules (SMs) have attracted intense attention due to their definite molecular structures, less batch‐to‐batch variation, and easier structure control. Herein, two new SM donors based on substituted isatin unit (DI3T, DI3T‐2F) are synthesized and applied as electron donors with the mixture of PC₇₁BM to construct organic photovoltaics. As a result, 5,6‐difluoro isatin derivative (DI3T‐2F) obtains a power conversion efficiency of 7.80% by a simple solution spin‐coating fabrication process without any additives, solvent, or thermal annealing process. More intuitively, due to stronger intermolecular interaction and higher hole mobility after the incorporation of fluorine atoms in end units, the devices present good tolerance to active layer thickness. The results indicate that DI3T‐2F shows promising potential for large‐scale printing processes and flexible application of efficient small molecule organic solar cells.     

Efficient Inverted Perovskite Solar Cells by Employing N‐Type (D–A1–D–A2) Polymers as Electron Transporting Layer

It is highly desirable to employ n‐type polymers as electron transporting layers (ETLs) in inverted perovskite solar cells (PSCs) due to their good electron mobility, high hydrophobicity, and simplicity of film forming. In this research, the capability of three n‐type donor–acceptor₁–donor–acceptor₂ (D–A₁–D–A₂) conjugated polymers (pBTT, pBTTz, and pSNT) is first explored as ETLs because these polymers possess electron mobilities as high as 0.92, 0.46, and 4.87 cm² (Vs)^?1 in n‐channel organic transistors, respectively. The main structural difference among pBTT, pBTTz, and pSNT is the position of sp²‐nitrogen atoms (sp²‐N) in the polymer main chains. Therefore, the effect of different substitution positions on the PSC performances is comprehensively studied. The as‐fabricated p–i–n PSCs with pBTT, pBTTz, and pSNT as ETLs show the maximum photoconversion efficiencies of 12.8%, 14.4%, and 12.0%, respectively. To be highlighted, pBTTz‐based device can maintain 80% of its stability after ten days due to its good hydrophobicity, which is further confirmed by a contact angle technique. More importantly, the pBTTz‐based device shows a neglected hysteresis. This study reveals that the n‐type polymers can be promising candidates as ETLs to approach solution‐processed highly‐efficient inverted PSCs.