Developing Efficient Benzene Additives for 19.43% Efficiency of Organic Solar Cells by Crossbreeding Effect of Fluorination and Bromination

Abstract

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5‐trifluorobenzene, hexafluorobenzene, 1,3,5‐tribromo‐2,4,6‐trifluorobenzene (TFTB), 1,3,5‐tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz‐F:PM6:L8‐BO system.

Crossbreeding Effect of Chalcogenation and Iodination on Benzene Additives Enables Optimized Morphology and 19.68% Efficiency of Organic Solar Cells

“…As for the functional groups used in solid additives, halogen atoms (F, Cl, Br, and I) are most commonly investigated, and a number of efficient solid additives with halogen atoms have been developed by different research groups. [17,26,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] These halogen atoms provide diverse weakbonding interactions with the photoactive materials for morphology optimization, and the volatilizable nature makes them easily removed to ensure morphological stability. [28,30,34] In addition to halogen atoms, oxygen atoms have also been widely introduced to develop additives by some groups.…”

“…[ 11 , 12 , 13 , 14 ] The most salient feature of an ideal morphology is recognized to be a bicontinuous interpenetrating network formed by the spontaneous phase separation of premixed donor and acceptor materials in the photoactive layer. [ 15 , 16 , 17 , 18 ] Nevertheless, we can hardly obtain such an ideal morphology in the as‐cast photoactive layer solely depending on the natural properties of donor and acceptor materials because the final morphology is not only determined by their inherent properties but also affected by different processing conditions. [ 11 , 17 ] Therefore, it is of great need to develop appropriate strategies to optimize the morphology according to the inherent properties of certain photoactive materials for maximizing the performances of BHJ‐OSCs.…”

“…This makes the solvent additives, which have ever been extensively used in fullerene‐based OSCs, [ 19 ] confront challenges in optimizing the morphology of NFA‐based photoactive layers via the selective solubility mechanism. [ 17 , 20 ] Alternatively, employing volatile solid additives has been emerging as a potential method to optimize the morphology of currently prevailing NFA‐based OSCs. [ 12 , 21 , 22 , 23 , 24 ] Volatile solid additives typically encompass a small aromatic core attached to various functional groups, making them have intrinsically high crystallinity and versatile noncovalent intermolecular interactions.…”

Selecting Solid Additives to Control the Interaction between Polymer Donors and Additives for Constructing High-Efficiency Organic Solar Cells

“…Although the intermolecular noncovalent interactions resulting from conjugated solid additives with blend layers have been extensively studied, most conclusions only discuss the interaction between electron-rich additives and SMAs because of their charge distribution properties. , There are few studies regarding the intermolecular interactions and functional mechanisms between solid additives and donor materials. , Polymer donors typically consist of D–A or D-π–A-π repeat units, which also contain electron-withdrawing (A) structural units, especially fluorinated A units with a relatively good π-conjugate plane. − Therefore, the interaction between donor materials and solid additives should not be ignored when investigating the ordered packing of BHJ OSC active layers.…”

Cyano-functionalized pyrazine: an electron-deficient unit as a solid additive enables binary organic solar cells with 19.67% efficiency

“…Subsequently, various solid additives were developed yielding PCEs over 19% for binary or ternary device systems. 58–62 Although these solid additives have made significant breakthroughs in improving the device performance, it is still necessary to develop new solid additives to better understand the working mechanism. Most of the previously reported solid additives are based on benzene or thiophene units (Fig.…”