Shamrock-Shaped Nonfullerene Acceptors Containing Nonhalogenated End Groups for High-Voltage Organic Photovoltaics

Abstract

Rapidly substantial progress with power conversion efficiency (PCE) over 19% for organic photovoltaics (OPVs) has been achieved contributed to the advent of exceptional-performance banana-shaped Y-series nonfullerene acceptors (NFAs). However, the open-circuit voltages (VOCs) of these high-efficiency materials are typically lower than 1.0 V due to the relatively low LUMO energy level. Therefore, developing new material systems simultaneously possessing high VOC and PCE has consistently been a focal research. Recently, our groups successfully obtained a novel A-DA'D-A type shamrock-shaped NFA via utlizing large conjugated acenaphtho[1,2-b]quinoxaline imide (AQI) unit as central core (A' unit) and fluorinated-IC as end groups, which exhibited a PCE of 18% with a VOC of 0.95 V. To further extend the familly of shamrock-shaped NFAs and upgrade their photovoltaic properties, herein, another new shamrock-shaped NFA containing non-halogenated end group IC was synthesized and named as AQI1. The reasonable cooperation of AQI and IC could facilitate to obtain upshifted LUMO energy level, resulting in a decreased energy loss in OPVs. Using classic p-type polymer PM6 and a benzotriazole-based linear polymer PE4 as donors, both devices can achieve high VOC of 1.06 V and 1.02 V respectively. Finally, PM6:AQI1 and PE4:AQI1 combinations realized PCEs of 11.3% and 13.7% respectively, suggesting that benzotriazole-based polymers might be better choice to blend with shamrock-shaped NFAs. These results indicate that shamrock-shaped NFAs with nonhalogenated end groups may be a feasible and potential design strategy to achieve low-cost and high-VOC OPVs.

Keywords: Organic photovoltaics, Shamrock-shaped NFAs, Non-halogenated end groups, High open-circuit voltage