Synergistic enhancement in open-circuit voltage and photovoltaic performance via linear naphthyldithiophene building block

Abstract

Among various photovoltaic building blocks, fused aromatic units such as benzo[1,2-b:4,5-b']dithiophene (BDT) based conjugated polymers have exhibited excellent photovoltaic properties in organic solar cells (OSCs) due to their better delocalization along polymeric backbones. However, further extending conjugation in fused aromatic units appears some unavailable drawbacks such low-solubility, low-antioxidation ability, high-lying HOMO level, etc., which cause negative effect on the corresponding open-circuit voltage (Voc) and power conversion efficiency (PCE). Here, we designed and synthesized two novel wide band gap polymers, PBDT-3T and PNDT-3T, using benzodithiophene and naphthyldithiophene as donor units and ester-substituted triple thiophenes as acceptor units. Comparing to the referenced BDT based polymer, it was found that NDT unit not only extends the conjugated degree of the main chain and increase polymeric crystallinity and carrier mobility, but also increases the Voc of NDT based photovoltaic device. The final short-circuit current and fill factor are 15.90 mA cm−2 and 63.7%, and finally the PCE reached 9.72%, which exhibited better advantages than the BDT unit polymers. Therefore, the adoption of NDT as photovoltaic building block is proved to be an effective strategy in synergistic improvement in Voc and PCE and could be referenced to other photovoltaic materials.