Synthesis and Optoelectronic Properties of Benzo[1,2‐b:4,5‐b′]dithiophene‐Based Copolymers with Conjugated 2‐(2‐Ethylhexyl)‐3,4‐dimethoxythiophene Side Chains

Abstract

In order to regulate the electronic ability of benzo [1,2-b:4,5-b′]dithiophene (BDT), the new electron-donating unit (BDTOT) is designed and synthesized which consists of a BDT backbone with conjugated 2-(2-ethylhexyl)-3,4-dimethoxythiophene side chains. By alternating copolymerization of BDTOT with electron-accepting units of fluorinated benzothiadiazole (FBT), benzothiadiazole (BT), and pyrrolo[3,4-c]pyrrole-1,4-dione (DPP), three donor-acceptor (D-A) copolymers (PBDTOT-FBT, PBDTOT-BT, and PBDTOT-DPP) have been developed for PSC applications. The impact of dimethoxythiophene substituent and the electron-accepting strength of the acceptor units on the absorption, HOMO/LUMO energy levels, and photovoltaic properties of the resultant polymers is investigated in detail. PBDTOT-BT and PBDTOT-DPP exhibit relatively narrower bandgaps and PBDTOT-FBT possesses a down-shifted HOMO energy level as compared to their corresponding analogs without methoxy groups onto the conjugated thiophene side chains. The screening of the different blend ratio, the processing additive, and polar solvent post-treatment is conducted to optimize the polymer solar cell (PSC) devices. PSCs with PBDTOT-FBT as donor deliver a power conversion efficiency (PCE) of 2.55%. By treatment of the active layer with methanol to tailor the morphology, the solar cell based on PBDTOT-FBT exhibits the remarkably improved PCE of 4.84% with a V oc of 0.92 V, a J sc of 8.71 mA cm −2 , and an FF of 60.3%.

Initial Engineering and Outdoor Stability Assessment of “Gray/Black” Fullerene-Free Organic Photovoltaics Based on Only Two Complementary Absorbing Materials: A Tetrabenzotriazacorrole and a Subphthalocyanine

“…This complexity limits and challenges the understanding of the role of each material in the optoelectronic phenomenon and thus their development. Similar approaches have been addressed using ternary mixtures within bulk-heterojunction OPVs − including the use of copolymers synthesized by the combination of electron-deficient and electron-rich comonomers, so-called push–pull or donor–acceptor polymers, through relatively difficult synthetic processes. − The bulk-heterojunction architecture also often leads to an increased complexity of engineering the OPV systems due to the nanophase morphology. This inhibits understanding and decouples the relationship between the molecular structure of each material and the morphology of the active layer on the optics, charge transport, and performance of the device.…”

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

“…Compared with the PBDTDPPcbp: PCBM based OSC, the substitution of 11-ethyltricosane increases the miscibility of PDPPBDT, thereby the J sc (7.12 mA/cm 2 ) and FF (62%) in PDPPBDT: PC 71 BM based OSC both enhanced, which further proves the above-conclusions. Subsequently, based on the alkyl chain substituted PPD unit, PQ3 (2015) was reported by Liu et al [136] ; PBDTBA(H)-DPP (2015) andPBDTBPA(F)-DPP (2015) were prepared by Chakravarthi et al [147] ; PBDTS-DPP (2016) ,PBDTOT-DPP (2016) and P2 (2016) were synthesized by Zhang et al [73] , Wang et al [148] and Kranthiraja et al [139] , respectively. Similarly,PBDTT-S-DPP (2016) , [149] PBDTT-Se-DPP (2016) , [149] P3 (2016) , [150] P7(0.0: 1.0) (2016) , [151] PDPP-BDT (2021) [152] and PDPP-BDT-Cl (2021) [152] were also prepared in subsequence.…”

“…Subsequently, considering further enhancing the electronegativity of acceptor unit in the main-chain engineering is an effective molecular design strategy, Shen et al [163] and Liu et al [136] based on the polymer backbone BDT-TR-BTDz-TR, reported PBTFBT (2013) and PB4 (2015) by introducing two "F" atoms into the BTDz unit. Afterward, PBDT2FBT-Th (2015) , [273] PBDT2FBT-Ph (2015) , [273] PBDTS-DTFBT (2016) , [73] PBDTOT-FBT (2016) , [73] PBDTOT-BT (2016) , [148] PBDTBP-DTffBT (2016) , [274] P1(1.0: 0.0) (2016) , [151] PBDT-DTBTff (2017) , [57] P3 (2017) , [268] PBDTEDOT-FBT (2018) , [269] PBDT-FBT (2018) , [275] PBDTF-FBT (2018) , [275] PBDTS-FBT (2018) , [275] PBDTSF-FBT (2018) [275] and PBTF (2018) [276] were also successfully synthesized. Among these donors, due to "F" atom with a strong electron-withdrawing optimizes the HOMO energy level of polymer donors as well as promotes the hole/electron mobility in corresponding OSCs.…”

Two-Dimensional Copolymers Based on an Alkylthionaphthyl-Substituted Benzo[1,2-b:4,5-b′]dithiophene for High-Efficiency Polymer Solar Cells

“…A breakthrough with a PCE of 9.29% was made by Yang and coworkers in 2016, in which an unsubstituted BDT was used to construct the novel D–A polymer of PBDT-DTFFBT . Also, two-dimensional (2D) BDT polymers have been presented in recent years and have showed improved photovoltaic properties over those of 1D BDT polymers. − Among these D–A polymers with a BDT unit, it is found that different acceptor units, such as ester-substituted thieno­[3,4- b ]­thiophene (TT), benzo­[ c ]­[1,2,5]­thiadiazole (BT), and benzo­[1,2- b :4,5- b ′]­dithiophene-4,8-dione (BDD) played an important role in improvement of photovoltaic performance. − Therefore, it is very important to alternate donor and acceptor units for constructing high-performance D–A photovoltaic polymers.…”