Wide Bandgap Copolymers Based on Quinoxalino[6,5‐f].quinoxaline for Highly Efficient Nonfullerene Polymer Solar Cells

Abstract

Two novel wide bandgap copolymers based on quinoxalino[6,5-f ]quinoxaline (NQx) acceptor block, PBDT-NQx and PBDTS-NQx, are successfully synthesized for efficient nonfullerene polymer solar cells (PSCs). The attached conjugated side chains on both benzodithiophene (BDT) and NQx endow the resulting copolymers with low-lying highest occupied molecular orbital (HOMO) levels. The sulfur atom insertion further reduces the HOMO level of PBDTS-NQx to −5.31 eV, contributing to a high open-circuit voltage, V oc , of 0.91 V. Conjugated n-octylthienyl side chains attached on the NQx skeletons also significantly improve the π-π* transitions and optical absorptions of the copolymers in the region of short wavelengths, which induce a good complementary absorption when blending with the low bandgap small molecular acceptor of 3,9 -bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2b:5,6-b′]dithiophene. The wide absorption range makes the active blends absorb more photons, giving rise to a high short-circuit current density, J sc , value of 15.62 mA cm −2 . The sulfur atom insertion also enhances the crystallinity of PBDTS-NQx and presents its blend film with a favorable nanophase separation, resulting in improved J sc and fill factor (FF) values with a high power conversion efficiency of 11.47%. This work not only provides a new fused ring acceptor block (NQx) for constructing high-performance wide bandgap copolymers but also provides the NQx-based copolymers for achieving highly efficient nonfullerene PSCs.

Synthesis and characterization of a wide‐bandgap polymer based on perfluorinated and alkylthiolated benzodithiophene with a deep highest occupied molecular orbital level for organic photovoltaics

“…We also compared the optical properties of P2FS‐ttTPD with those of the unsubstituted BDTT‐ttTPD‐based polymer PBDTT‐ttTPD. [ 30–34 ] Note also that the introduction of the electron‐withdrawing fluorine (F) and alkylthiyl (SR) groups strongly blue‐shifts the absorption peaks, which is consistent with the results of other studies. The optical bandgap energy ( E g ) is also affected by the presence of the F and SR groups.…”

Highly Efficient Non‐Fullerene Polymer Solar Cells Enabled by Wide Bandgap Copolymers With Conjugated Selenyl Side Chains

“…As shown in Figure , the thermogravimetric analysis (TGA) profiles revealed that the decomposition temperatures (T d s, 5% weight loss) were 400 and 330 °C for PBDT‐Se‐TAZ and PBDTS‐Se‐TAZ, indicting their good thermal stability. The lower bonding energy of CS than CC induced the reduced T d of PBDTS‐Se‐TAZ, which was consistent with the previous observations . The differential scanning calorimetry (DSC) analysis was also conducted to study the thermal properties of these two copolymers (Figure b).…”

Achieving a High Fill Factor and Stability in Perylene Diimide–Based Polymer Solar Cells Using the Molecular Lock Effect between 4,4′‐Bipyridine and a Tri(8‐hydroxyquinoline)aluminum(III) Core

“…The α values were calculated to be 0.935 and 0.958 for PTTEA : Alq 3 ‐PDI and PTTEA : Alq 3 ‐PDI2 , respectively, which signified that bimolecular recombination was negligible in the PTTEA : Alq 3 ‐PDI2 devices. The dependence of V oc on P light for PTTEA : Alq 3 ‐PDI and PTTEA : Alq 3 ‐PDI2 was measured to be 1.26 kT e −1 and 1.19 kT e −1 , respectively, indicating less charge‐trapped recombination in the PTTEA : Alq 3 ‐PDI2 devices . Less charge recombination can improve the charge collection efficiency.…”