High‐Efficiency Organic Solar Cells Enabled by Chalcogen Containing Branched Chain Engineering: Balancing Short‐Circuit Current and Open‐Circuit Voltage, Enhancing Fill Factor

Abstract

The elaborate balance between the open‐circuit voltage (VOC) and the short‐circuit current density (JSC) is critical to ensure efficient organic solar cells (OSCs). Herein, the chalcogen containing branched chain engineering is employed to address this dilemma. Three novel nonfullerene acceptors (NFAs), named BTP‐2O, BTP‐O‐S, and BTP‐2S, featuring different peripheral chalcogen containing branched chains are synthesized. Compared with symmetric BTP‐2O and BTP‐2S grafting two alkoxy or alkylthio branched chains, the asymmetric BTP‐O‐S grafting one alkoxy and one alkylthio branched chains shows mediate absorption range, applicable miscibility, and favorable crystallinity. Benefiting from the enhanced π–π stacking and charge transport, an optimal power conversion efficiency (PCE) of 17.3% is obtained for the PM6:BTP‐O‐S‐based devices, with a good balance between VOC (0.912 V) and JSC (24.5 mA cm−2), and a high fill factor (FF) of 0.775, which is much higher than those of BTP‐2O (16.1%) and BTP‐2S‐based (16.4%) devices. Such a result represents one of the highest efficiencies among the binary OSCs with VOC surpassing 0.9 V. Moreover, the BTP‐O‐S‐based devices fabricated by using green solvent yield a satisfactory PCE of 17.1%. This work highlights the synergistic effect of alkoxy and alkylthio branched chains for high‐performance OSCs by alleviating voltage loss and enhancing FF.

Fine-Tuning of Polymer Aggregation Properties via Regulating the Side Chain Arrangement for Efficient Organic Solar Cells

“…Side chain engineering of organic semiconductors has been proved to be an effective method to realize highly efficient OSCs because the side chains have great influence on the optoelectronic properties, intermolecular interactions, and bulk heterojunction morphology. − It is found in previous researches that finely tuning the size, , isomerization, , adjusting the branching positions, desymmetrization, , or introducing chalcogen-containing alkyl chains on organic semiconductors can significantly affect their exciton dissociation, charge transport, and charge recombination in the devices, resulting in substantial differences in device performance. However, it is noted that these researches have mainly focused on state-of-the-art high-performance ladder-type nonfullerene SMAs during the past few years, whereas less attention has been focused on the side chains on the polymers.…”

High-Performance Nonfused Electron Acceptor with Precisely Controlled Side Chain Fluorination

“…For example, changing the backbone constituent from thiophene units to selenium moieties, tuning the size of π-conjugated core, introducing electron-withdrawing or electron-donating groups (i.e., through fluorination, , chlorination, , methoxylation, and methylation), and π-extending the ending 1,1-dicyanomethylene-3-indanone groups have been extensively reported to tune the macroscopic properties of nonfullerene SMAs. In addition, proper side chains are also critical because they have a great influence on the absorption, energy levels, solution processability, molecular packing, as well as intermolecular interactions, which all play substantial roles in manipulating the device efficiency of OSCs. − …”

Silane or Siloxane‐Side‐Chain Engineering of Photovoltaic Materials for Organic Solar Cells†

“…The alkyl, alkoxy, thioalkyl side chain, as well as halogen, hydroxyl, and ester side chain are frequently‐used side chains. [ 20 ] The introduction of side chains not only influences the molecular solubility and crystallinity, but could provide notable advantages in enhancing charge mobility and optimizing intermolecular packing. [ 21‐25 ] Therefore, appropriate side chain modifications can improve the photovoltaic performance effectively.…”