Head-to-Head Linkage Containing Dialkoxybithiophene-Based Polymeric Semiconductors for Polymer Solar Cells with Large Open-Circuit Voltages

Abstract

High degree of polymer backbone planarity is achieved by incorporating intramolecular noncovalent sulfur••• oxygen interaction, which also affords good solubility by attaching alkoxy chains at the 3,3′-positions of bithiophene. However, the applications of the resulting polymers are plagued by their highlying HOMOs due to the strong electron-donating alkoxy chains, resulting in small open-circuit voltages (V oc s) in polymer solar cells. Herein, a novel head-to-head linkage containing 3,3′dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) is invented. Single-crystal X-ray diffraction shows direct evidence of noncovalent sulfur•••oxygen interaction and coplanar backbone of BTCNOR. Very low-lying HOMOs (−5.5 to −5.6 eV) of the corresponding polymers with high degree of backbone planarity and good solubility are achieved by introducing strong electronwithdrawing cyano group onto the dialkoxybithiophene. The cyano offsets the effect of the electron-donating alkoxy chain, rendering the new BTCNOR as a weak donor unit. With this approach, polymer solar cells fabricated from BTCNOR-based polymers deliver very large V oc s (0.9−1.0 V). By varying the BTCNOR side chains, the highest power conversion efficiency of 7.13% is obtained. Diverse characterization techniques are performed to elucidate the structure−property correlations of the new BTCNOR-based semiconductors. The results demonstrate that incorporating strong electron-withdrawing groups into the highly electron-rich dialkoxybithiophene can lead to improved optoelectrical property. The study offers a promising materials design strategy for high-performance organic electronics.

Fluorinated Head‐to‐Head Dialkoxybithiophene: A New Electron‐Donating Building Block for High‐Performance Polymer Semiconductors

“…Single crystals of building blocks can provide insights into backbone conformation, intramolecular noncovalent interactions, and intermolecular packing structure of the resulting polymers . Thus, the single crystal of the compound 9 was grown by diffusing ethanol into its dichloromethane solution and X‐ray diffraction data were collected (Table S1, Supporting Information).…”

“…[25,55] Thus, the single crystal of the compound 9 was grown by diffusing ethanol into its dichloromethane solution and X-ray diffraction data were collected (Table S1, Supporting Information). [25,55] Thus, the single crystal of the compound 9 was grown by diffusing ethanol into its dichloromethane solution and X-ray diffraction data were collected (Table S1, Supporting Information).…”

“…To further optimize frontier molecular orbitals (FMOs) of head‐to‐head containing building blocks, we designed and synthesized a cyano‐functionalized dialkoxy bithiophene (BTCNOR, Figure d). The strong electron‐withdrawing cyano group leads to greatly decreased HOMO (−5.60 eV) for the BTCNOR‐benzodithiophene copolymers, thus a remarkable high V oc up to 1.0 V in OSCs was achieved . However, due to its high electron‐deficiency, the stannylation of BTCNOR failed to yield pure monomer, and the Stille coupling‐based polycondensation was unsuccessful.…”

3,4‐Dicyanothiophene—a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

“…In most cases additional electron‐withdrawing substituents are still needed on the comonomers 18–20. Another functional group that deserves attention is the cyano group, which possesses a very strong electron‐withdrawing ability and will not cause significant twist with adjacent units via rational design 21. Due to these merits, the cyano group was successfully used in constructing high‐performance n‐type conjugated polymers,22 although its application in p‐type materials21,23 has received less attention.…”

Polymer semiconductors incorporating head-to-head linked 4-alkoxy-5-(3-alkylthiophen-2-yl)thiazole

“…11,31,32 To counterbalance the strong electron-donating effect of alkoxy chains, the alkoxy-functionalized HH bithiophenes should be modied for lowering FMO levels. [33][34][35] Herein, we report the design and synthesis of a novel HH linked building block, 4-alkoxy-5-(3-alkylthiophen-2-yl)thiazole (TRTzOR) ( Fig. 1c), in which the electron-decient thiazole was adopted to replace the electron-rich thiophene unit.…”