Precisely Manipulating Molecular Packing via Tuning Alkyl Side‐Chain Topology Enabling High‐Performance Nonfused‐Ring Electron Acceptors

Abstract

In the development of high‐performance organic solar cells (OSCs), the self‐organization of organic semiconductors plays a crucial role. This study focuses on the precisely manipulation of molecular assemble via tuning alkyl side‐chain topology in a series of low‐cost nonfused‐ring electron acceptors (NFREAs). Among the three NFREAs investigated, DPA‐4, which possesses an asymmetric alkyl side‐chain length, exhibits a tight packing in the crystal and high crystallinity in the film, contributing to improved electron mobility and favorable film morphology for DPA‐4. As a result, the OSC device based on DPA‐4 achieves an excellent power conversion efficiency of 16.67%, ranking among the highest efficiencies for NFREA‐based OSCs.

Low-Cost Nonfused-Ring Electron Acceptors Enabled by Noncovalent Conformational Locks

“…Therefore, we believe that more efforts should be dedicated to further enhancing the photovoltaic performance, reducing the product cost, and improving the device stability of NFREAs and PNFREAs from aspects such as molecular design, donor/acceptor pairs, and synthetic routes. Recently, we have conducted a thorough theoretical analysis that deepened our understanding of the fundamental nature of NoCLs and led to the development of a simple descriptor ( S ) to quantify their strength . Our findings indicate that the S values follow the order of S···F < Se···F and S···O < Se···O, suggesting that the incorporation of Se···F and Se···O NoCLs in the design of NFREAs could potentially have a more significant impact on restricting the free rotation of C–C bonds and locking the planar conformation. Bulky side chains, such as 2,6-dialkylphenyl, 2,6-dialkyloxyphenyl, and diphenylamino, have been recognized in the design of NFREAs. − These sterically hindered side chains enforce them to be almost perpendicular to the π-conjugated backbones, thereby enhancing the coplanarity. It is believed that the coexistence of bulky side chains and NoCLs will be beneficial for the development of highly planar NFREAs through a dual-lock effect. The typical photoactive layer is composed of a combination of donor and acceptor materials.…”

“…Bulky side chains, such as 2,6-dialkylphenyl, 2,6-dialkyloxyphenyl, and diphenylamino, have been recognized in the design of NFREAs. − These sterically hindered side chains enforce them to be almost perpendicular to the π-conjugated backbones, thereby enhancing the coplanarity. It is believed that the coexistence of bulky side chains and NoCLs will be beneficial for the development of highly planar NFREAs through a dual-lock effect.…”

Hybrid Nonfused Electron Acceptors with Perylene Diimide Pendants for Organic Solar Cells

“…Compared to the fused electron acceptors, the nonfused electron acceptors (NFEAs) have gained significant attention, as they can balance PCEs and material costs. − In 2017, NFEAs were first applied to the OSCs by Bo et al, where intramolecular noncovalent NFEAs can lock the planar conformation, leading to efficient charge transport . During the past few years, much effort has enabled OSCs based on NFEAs to achieve PCE above 17%, − demonstrating great potential for pushing the limits of OSC technology in terms of efficiency and material cost. Looking into the history of nonfullerene electron acceptors, we can find that the new molecular design is a key factor in enhancing the performance of OSCs. − …”