LAUSR

Morphology control is one of the key strategies in optimizing the performance of organic photovoltaic materials, particularly for diketopyrrolopyrrole (DPP)-based donor polymers. The design of DPP-based polymers that provide high power conversion efficiency (PCE) presents a significant challenge that requires optimization of both energetics and morphology. Herein, a series of high performance, small band gap DPP-based terpolymers are designed via two-step side chain engineering, namely introducing alternating short and long alkyls for reducing the domain spacing and inserting alkylthio for modulating the energy levels. The new DPP-based terpolymers are compared to delineate how the side chain impacts the mesoscale morphology. By employing the alkylthio-substituted terpolymer PBDPP-TS, the new polymer solar cell (PSC) device realizes a good balance of a high Voc of 0.77 V and a high Jsc over 15 mA cm−2, and thus realizes desirable PCE in excess of 8% and 9.5% in single junction and tandem PSC devices, respectively. The study indicates better control of domain purity will greatly improve performance of single junction DPP-based PSCs toward 10% efficiency. More significantly, the utility of this stepwise side chain engineering can be readily expanded to other classes of well-defined copolymers and triggers efficiency breakthroughs in novel terpolymers for photovoltaic and related electronic applications.