Modular‐Approach Synthesis of Giant Molecule Acceptors via Lewis‐Acid‐Catalyzed Knoevenagel Condensation for Stable Polymer Solar Cells

Abstract

The operational stability of polymer solar cells is a critical concern with respect to the thermodynamic relaxation of acceptor‐donor‐acceptor (A‐D‐A) or A‐DA'D‐A structured small‐molecule acceptors (SMAs) within their blends with polymer donors. Giant molecule acceptors (GMAs) bearing SMAs as subunits offer a solution to this issue, while their classical synthesis via the Stille coupling suffers from low reaction efficiency and difficulty in obtaining mono‐brominated SMA, rendering the approach impractical for their large‐scale and low‐cost preparation. In this study, we present a simple and cost‐effective solution to this challenge through Lewis acid‐catalyzed Knoevenagel condensation with boron trifluoride etherate (BF3 ⋅ OEt2) as catalyst. We demonstrated that the coupling of the monoaldehyde‐terminated A‐D‐CHO unit and the methylene‐based A‐link‐A (or its silyl enol ether counterpart) substrates can be quantitatively achieved within 30 minutes in the presence of acetic anhydride, affording a variety of GMAs connected via the flexible and conjugated linkers. The photophysical properties was fully studied, yielding a high device efficiency of over 18 %. Our findings offer a promising alternative for the modular synthesis of GMAs with high yields, easier work up, and the widespread application of such methodology will undoubtedly accelerate the progress of stable polymer solar cells.

Recent progress and prospects of dimer and multimer acceptors for efficient and stable polymer solar cells

“…Very recently, the Zhang group demonstrated an effective method to enable the synthesis of discrete end-linked DSMAs with much improved yields. 164 First, they synthesized asymmetric monoaldehyde-terminated SMA units and coupled these with various diboronated linkers. Specifically, they employed a Lewis-acid-catalyzed Knoevenagel condensation, using boron trifluoride etherate (BF3·OEt2) as a catalyst.…”

Noncovalent Interaction Boosts Performance and Stability of Organic Solar Cells Based on Giant-Molecule Acceptors

“…In the last 2 years, giant-molecule acceptors, which connect two or three Y-series derivatives with a thiophene or other conjugated segments as the linker, have been considered a good candidate to merge the advantages of small-molecule NF acceptors and polymeric acceptors, such as an accurate molecular structure, easy repeatability, and stable morphology. − For example, Zou and co-workers designed two dimeric acceptors, and the related device showed a PCE of 17.06% . Wei and co-workers reported a trimeric acceptor G-Trimer by incorporating a benzotrithiophene core and three Y6 derivatives as the arms, and the G-Trimer-based OSCs showed longer-term stability as well as higher photovoltaic performance than the OSC based on the dimeric acceptor G-Dimer .…”

Reducing the Depletion Region Width at the Anode Interface via a Highly Doped Conjugated Polyelectrolyte Composite for Efficient Organic Solar Cells

“…Recognized for their lightweight and flexibility, organic solar cells (OSCs) are pivotal in the evolution of next-generation photovoltaics, primarily due to their compatibility with cost-effective solution processing techniques for fabricating large-area panels. − The power conversion efficiency (PCE) of OSCs now surpasses the 18% threshold, signifying their potential for practical applications, as indicated by numerous studies. − Despite these advancements, most improvements in photovoltaic efficiencies are attributed to developments in active layer materials, with modifications in electrode design, particularly at the anode, being less explored. − The range and types of interfacial materials for anode modification in OSCs are currently limited, which is a significant barrier to further progress in this domain. − Considering the high expenditure and limited scope for advancement with new active layer materials, innovations in anode modification stand out as a promising direction. Such modifications, aimed at reducing the interfacial resistance and facilitating hole transport, could potentially enhance the OSC performance.…”