Enhancing the n‐Type Conductivity and Thermoelectric Performance of Donor–Acceptor Copolymers through Donor Engineering

Abstract

Conjugated polymers with high thermoelectric performance enable the fabrication of low-cost, large-area, low-toxicity, and highly flexible thermoelectric devices. However, compared to their p-type counterparts, n-type polymer thermoelectric materials show much lower performance, which is largely due to inefficient doping and a much lower conductivity. Herein, it is reported that the development of a donor-acceptor (D-A) polymer with enhanced n-doping efficiency through donor engineering of the polymer backbone. Both a high n-type electrical conductivity of 1.30 S cm and an excellent power factor (PF) of 4.65 µW mK are obtained, which are the highest reported values among D-A polymers. The results of multiple characterization techniques indicate that electron-withdrawing modification of the donor units enhances the electron affinity of the polymer and changes the polymer packing orientation, leading to substantially improved miscibility and n-doping efficiency. Unlike previous studies in which improving the polymer-dopant miscibility typically resulted in lower mobilities, the strategy maintains the mobility of the polymer. All these factors lead to prominent enhancement of three orders magnitude in both the electrical conductivity and the PF compared to those of the non-engineered polymer. The results demonstrate that proper donor engineering can enhance the n-doping efficiency, electrical conductivity, and thermoelectric performance of D-A copolymers.

A thermally activated and highly miscible dopant for n-type organic thermoelectrics

“…11). Thus, TAM + cations can be stabilized in alkyl side-chain regions, whereas the N-DMBI + cations are "crowded out" by the alkyl chains to empty space, suggesting that N-DMBI doping could lead to severe phase seperations 11,22,24 . All these results demonstrate that TAM have better dopant-semiconductor miscibility than N-DMBI and TAM doping can form a "dopant-at-side-chain" microstructures.…”

“…f Thermoelectric performance comparison of TAM-doped FBDPPV with literature results (refs. 11,24,[26][27][28][29][30][53][54][55][56][57][58] ). Error bars indicate the SD of ten experimental replicates.…”

“…For instance, 1,3dimethyl-2-phenylbenzimidazoline (DMBI)-based hydride dopants can even n-dope p-type materials such as 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) 23 . However, these dopants still lack solution stability and miscibility with organic semiconductors 11,24 . To overcome the immiscibility, modification of semiconductor backbone using polar side chain or twisted conjugated building blocks are developed; however, these strategies usually significantly change the charge transport property of organic semiconductors, e.g., leading to much lower charge carrier mobility [25][26][27][28] .…”

Electron transport in a sequentially doped naphthalene diimide polymer

“…[17][18][19] One reason is that the dopant-induced polaronic charge carriers tend to be localized on acceptor moieties, and the electronic coupling between adjacent acceptor sites is often poor. [20][21][22] Conjugated polymers incorporating naphthalene diimides (NDIs) comprise a prominent family of electron-transporting semiconducting polymers and are reduced at moderate potentials of ca. À1.0 V vs. ferrocene.…”

Molecules-based optoelectronic devices beyond traditional sandwich-like device configuration

“…分子基光电器件具有成本低廉, 性能易于调控, 可 大面积制备 [1][2][3] 以及适用于可穿戴柔性电子领域 [4,5] 等 特点, 受到了研究者和产业界的广泛关注. 分子基光电 器件的性能和功能不仅与分子半导体材料有关, 可通 过控制分子的结构来调控 [6][7][8][9][10][11][12][13][14] , 同时也与器件的结构 或构型密切相关 [15][16][17][18][19][20][21] . 经过化学家、材料学家数十年 的不懈努力, 目前高性能的有机半导体材料已经屡见 不鲜, 中国科学家在其中发挥重要作用, 并取得了一 系列突破 [17,22] .…”