Random terpolymer based on thiophene-thiazolothiazole unit enabling efficient non-fullerene organic solar cells

Jingnan Wu,Guangye Zhang,Jin Fang,Bing Guo,Yulong Wang,Lingeswaran Arunagiri,Xia Guo,Maojie Zhang,Feng Liu,Guangwei Li,He Yan,Lei Zhu,Yongfang Li

doi:10.1038/s41467-020-18378-9

Abstract

Developing a high-performance donor polymer is critical for achieving efficient non-fullerene organic solar cells (OSCs). Currently, most high-efficiency OSCs are based on a donor polymer named PM6, unfortunately, whose performance is highly sensitive to its molecular weight and thus has significant batch-to-batch variations. Here we report a donor polymer (named PM1) based on a random ternary polymerization strategy that enables highly efficient non-fullerene OSCs with efficiencies reaching 17.6%. Importantly, the PM1 polymer exhibits excellent batch-to-batch reproducibility. By including 20% of a weak electron-withdrawing thiophene-thiazolothiazole (TTz) into the PM6 polymer backbone, the resulting polymer (PM1) can maintain the positive effects (such as downshifted energy level and reduced miscibility) while minimize the negative ones (including reduced temperature-dependent aggregation property). With higher performance and greater synthesis reproducibility, the PM1 polymer has the promise to become the work-horse material for the non-fullerene OSC community.

Highlights

Developing a high-performance donor polymer is critical for achieving efficient non-fullerene organic solar cells (OSCs)
We carry out morphological and electronic characterizations on the polymer and show that the TTz unit can introduce several effects: (1) the TTz unit exhibits a near-perfect co-planar structure which could enhance the crystallinity of polymer and charge mobility; (2) the addition of the TTz unit can adjust the miscibility between the polymer and non-fullerene acceptor to achieve more favorable phase interface for high fill factor (FF); (3) the TTz unit has some negative effects on the temperature-dependent aggregation (TDA) property of the polymer, which is important to achieve optimal morphology and great OSC performance
The corresponding differential scanning calorimetry (DSC) measurement results are shown in Supplementary Fig. 3, but there are no clear endothermic peak and exothermic peak in the DSC thermogram

Summary

Introduction

Developing a high-performance donor polymer is critical for achieving efficient non-fullerene organic solar cells (OSCs). Owing to the stronger electronegativity of the sp2-nitrogen atom on TTz unit, the highest occupied molecular orbital (HOMO) levels of the terpolymers efficiently decreased[39,40,41], which could be beneficial to achieve higher Voc and lower energy loss (Eloss) in OSCs. Figure 1c and Supplementary Fig. 6a present the UV-vis absorption spectra of the four polymers in chloroform solutions and solid-state films, respectively.

Results

Conclusion