O-B(F)←N Functionalized Copolymers with Delayed Fluorescence and P-Type Semiconducting Characteristics.

Conjugated polymers with integrating properties of delayed fluorescence and photovoltaic responses simultaneously are scarcely reported due to the generally contradictory requirements for molecular structures to achieve the two properties. Herein, an O-B(F)←N functionalized fused unit (M) with multiple resonance features, small energy gap between lowest singlet excited state (S1) and triplet excited state (T1) (ΔEST = 0.23 eV), and delayed fluorescence (τD = 0.75 µs), is designed. Selecting three benzodithiophene (BDT) derivatives as co-units to copolymerize with M, leading to a series of O-B(F)←N embedded polymers also maintaining delayed fluorescence (τD = 0.4-0.5 µs). Moreover, p-type semiconductor characteristics are tested for these polymers with hole mobilities in the range of 10-6-10-5 cm2/Vs. Devices with obviously photovoltaic responses are prepared using these polymers as donors and Y6 as the acceptor, affording a preliminary efficiency of 5.05%. This work successfully demonstrates an effective strategy to design conjugated polymers with integrating properties of delayed fluorescence and photovoltaic performance simultaneously by introducing O-B(F)←N functional groups to polymer backbones.

Improving Photovoltaic Performance of All-Polymer Solar Cells by Adding an Amorphous B←N Embedded Polymer as the Third Component.

Currently, most of the disclosed ternary strategies to improve photovoltaic performance of all-polymer solar cells (all-PSCs) commonly focus on the guest polymers having similar structures with the host polymer donors or acceptors. Herein, this work develops a distinctive ternary method that adding an amorphous B←N embedded polymer named BN-Cl-2fT to a crystallized host polymer blend of PM6 (a commercialized polymer donor) and PY-TT (a copolymer of Y6 and thieno[3,2-b]thiophene). Although the structures between BN-Cl-2fT and PM6 and PY-TT are completely different, excellent miscibility is found between BN-Cl-2fT and both of the host PM6 and PY-TT, which can be interpreted by the crowded phenyl groups anchoring along the backbone of BN-Cl-2fT, leading to weak self-aggregation. Glazing incidence wide-angle X-ray diffraction (GIWAXS) measurements explicitly confirm the crystallization of PM6 and PY-TT and amorphous feature of BN-Cl-2fT. Furthermore, adding 10 wt% BN-Cl-2fT to PM6:PY-TT can significantly enhance the crystallization of the host polymers. Thus the ternary devices based on PM6:PY-TT:BN-Cl-2fT afford promote short-circuit current density (JSC , 23.29 vs. 21.80 mA cm-2 ), fill factor (FF, 62.4% vs. 60.0%), and power conversion efficiency (PCE, 13.70% vs. 12.23%) in contrast to these parameters of binary devices based on PM6:PY-TT. This work provides a unique and enlightening avenue to design high performance all-PSCs by adding amorphous B←N embedded polymers as guest component to enhance host-crystallization.