New Wide Bandgap Conjugated D‐A Copolymers Based on BDT or NDT Donor Unit and Anthra[1,2‐b:4,3,bʹ:6,7‐cʺ]trithiophene‐8‐12‐dione Acceptor for Fullerene‐Free Polymer Solar Cells

Abstract

Two donor-acceptor (D-A) copolymers, P128 and P129, containing benzodithiophene (BDT) and naphthiodithiophene (NDT) donor unit, respectively, and the alike anthra[1,2-b:4,3,bʹ:6,7-cʺ] trithiophene-8-12-dione(A3T) as an acceptor unit, are synthesized. The P129 (NDT donor) exhibits enhanced chain planarity and linearity of backbone compared to P128 (BDT donor), which leads to a considerable increase in both the light-harvesting ability and hole mobility. In addition to it, the incorporation of the NDT unit creates a strong modification in the morphology with a well-mixed interpenetrating nanofibrillar network with an increased donor-acceptor interface in the P129:Y6 bulk heterojunction active layer that leads to a high short-circuit current density and fill factor. The power conversion efficiency (PCE) of the improved polymer solar cells based on P128:Y6 and P129:Y6 is 6.25% and 14.55%, respectively. The negative HOMO offset (−0.02 eV) at P128/Y6 interface restricts the hole transfer from Y6 to P128 and results in low value of short-circuit current and thereby poor PCE. Finally, the ternary PSCs are constructed with a weight ratio of 0.5:0.5 between P128 and P129 and the weight component of Y6 is kept constant and the PSC attains a PCE of 16.19%. This increase in the PCE can be attributed to the formation of semiconducting alloy based on P128 and P129 donors and the transformation of HOMO offset from negative (−0.02 eV for Y6/P128) to positive (0.04 eV for Y6/P128:P129).

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

“…In addition, after adjusting the binding site of thiophene and benzene units, a series of novel polymer donors designed by introducing the donor unit benzo [2, 1-b : 3, 4-b '] dithiophene (BdT) were also successfully synthesized. In 2011, P128 (2011) was first reported by Keshtov and co-workers; [354] a series of novel polymer donors PBdT-DTBT (2011) ,PBdT-DPP (2011) , PBdT-TTz (2011) and PBdT-BTz (2011) were also prepared by Zhang et al [355] After applying for OSC devices, the formation of highly ππ conjugated structure endows such OSCs with a high V oc , especially for P128: Y6 based (0.92 V) and PBdT-TTz: PC 70 BM based (0.90 V) OSCs. Furthermore, P1 (2017) and PDTID-DTB(P2) (2022) were also successfully synthesized by Keshtov and co-workers.…”

“…Afterward, based on the reported results of P128, Keshtov and co-workers constructed the donor unit NdT by introducing benzene group to further extend the conjugated plane of BdT, followed by the synthesis ofP129 (2022) . [354] Notably, after blending with the acceptor Y6, P129: Y6 based OSC exhibited theV oc of 0.86 V, J sc of 23.58 mA/cm 2 , FF of 71% and PCE of 14.33%. Compared with P128: Y6 based OSC, the significantly optimized photovoltaic performance presented in P129: Y6 based OSC can be attributed to the formation of more complemental absorption and finer fibrous network morphology of P129: Y6 blend film.…”