Two novel wide-bandgap copolymers, PBDT-TDZ and PBDTS-TDZ, are developed based on 1,3,4-thiadiazole (TDZ) and benzo[1,2-b:4,5-b']dithiophene (BDT) building blocks. These copolymers exhibit wide bandgaps over 2.07 eV and low-lying highest occupied molecular orbital (HOMO) levels below -5.35 eV, which match well with the typical low-bandgap acceptor of ITIC, resulting in a good complementary absorption from 300 to 900 nm and a low HOMO level offset (≤0.13 eV). Compared to PBDT-TDZ, PBDTS-TDZ with alkylthio side chains exhibits the stronger optical absorption, lower-lying HOMO level, and higher crystallinity. By using a single green solvent of o-xylene, PBDTS-TDZ:ITIC devices exhibit a large open-circuit voltage (V ) up to 1.10 eV and an extremely low energy loss (E ) of 0.48 eV. At the same time, the desirable high short-circuit current density (J ) of 17.78 mA cm and fill factor of 65.4% are also obtained, giving rise to a high power conversion efficiency (PCE) of 12.80% without any additive and post-treatment. When adopting a homotandem device architecture, the PCE is further improved to 13.35% (certified as 13.19%) with a much larger V of 2.13 V, which is the best value for any type of homotandem organic solar cells reported so far.

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.

A novel wide-bandgap copolymer of PBDT-ODZ based on benzo[1,2-b:4,5-b' ]dithiophene (BDT) and 1,3,4-oxadiazole (ODZ) blocks is developed for efficient nonfullerene polymer solar cells (NF-PSCs). PBDT-ODZ exhibits a wide bandgap of 2.12 eV and a low-lying highest occupied molecular orbital (HOMO) level of -5.68 eV, which could match well with the low-bandgap acceptor of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylthienyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene (ITIC-Th), inducing a good complementary absorption from 300 to 800 nm and a minimal HOMO level offset (0.1 eV). The PBDT-ODZ:ITIC-Th devices exhibit a large open-circuit voltage (V ) of 1.08 eV and a low energy loss (E ) of 0.50 eV, delivering a high power conversion efficiency (PCE) of 10.12%. By adding a small amount of copper(I) iodide (CuI) as an additive to form coordination complexes in the active blends, much higher device performances are achieved due to the improved absorption and crystallinity. After incorporating 4% of CuI, the PCE is elevated to 12.34%, with a V of 1.06 V, a J of 17.1 mA cm and a fill factor of 68.1%. This work not only provides a novel oxadiazole-containing wide-bandgap polymeric donor candidate for high-performance NF-PSCs but also presents an efficient morphology-optimization approach to elevate the PCE of NF-PSCs for future practical applications.

In this work, the authors design and synthesize two novel wide bandgap copolymers based on selenophene substituted benzo[1,2‐b:4,5‐b']dithiophene (BDTSe) as the donor unit and fluorinated benzotriazole as the acceptor unit for high performance non‐fullerene polymer solar cells (NF‐PSCs). A larger maximum molar extinction coefficient (ϵ) of 8.54 × 104 M−1 cm−1 is achieved when introducing sulfur atom onto the two‐dimensional (2D) BDTSe units, which should realize the better complementary absorption with ITIC as the acceptor, leading to a higher Jsc of 19.51 mA cm−2. Furthermore, a lower highest occupied molecular orbital (HOMO) energy level with almost no change in bandgap can be also achieved after inserting the sulfur atoms, thus resulting in an enhanced open‐circuit voltage (Voc) of 0.84 V without sacrificing the short‐current density (Jsc). In addition, the higher crystallinity and optimized morphology are found to be beneficial to more efficient exciton dissociation and charge transport, giving rise to a higher fill factor (FF) of 75.1% and an elevated power conversion efficiency (PCE) of 12.31%. The results indicate that the strategy of alkylthioselenyl side chains on the BDT unit for constructing the donor‐acceptor (D‐A) copolymer donor materials is an excellent approach for realizing highly efficient NF‐PSCs.

Alkylthiothieyl substituted benzothiophene (BDT) and alkoxycarbonyl cyanovinyl modified thienothiophene (TT) were copolymerized to obtain a new two dimensional low band gap polymer PBDTTT-S-CN, which exhibited a promising efficiency of 7.0% in organic solar cells.