Syntheses and Photovoltaic Properties of Narrow Band Gap Donor–Acceptor Copolymers with Carboxylate-Substituted Benzodithiophene as Electron Acceptor Unit

Abstract

Stille-coupling of carboxylate-substituted dibrominated benzodithiophene (BDTC) with 2,5-distannylthieno- [3,4-b]thiophene gave novel donor−acceptor type alternating copolymers, PBDTC-TT, where BDTC works as an electronaccepting unit in the polymers. They showed broad absorption bands from 500 nm to the near-infrared region, optical band gap (E g ) about 1.5 eV, small π-stacking distance (3.6 Å), and good thermal stability. The hole mobilities of PBDTC-TT determined from performance of their organic field-effect transistors were 3.1−6.9 × 10 −4 (cm 2 V −1 s −1 ). The bulk heterojunction (BHJ) solar cells were fabricated with configuration of ITO/PEDOT:PSS/polymer:PC 70 BM/LiF/ Al. A PBDTC-TT device exhibited photocurrent response upon exposure to light with wavelength of 300−900 nm and incident photon to current conversion efficiency over 40% in the range of 400−750 nm. The power conversion efficiency of the best-performed device reached 3.03% with short-circuit current density of 12.54 mA cm −2 , fill factor of 0.48, and open circuit voltage of 0.51 V under illumination of AM 1.5 G/100 mW cm −2 . These results show that the BDTC unit can behave as an electron accepting building block for donor−acceptor type narrow band gap polymers, and these types of polymers can be used as a donor material in the active layer for BHJ photovoltaic cells.

Side-chain Engineering of Benzo[1,2-b:4,5-b’]dithiophene Core-structured Small Molecules for High-Performance Organic Solar Cells

“…The distance between SMs conjugated backbone separated by side chains can thus be calculated to be 19.4, 20.7, and 19.5 Å, respectively 33 36 . All of them also showed a weak diffraction at 2θ = 24.6°, indicating the π-stacking distance between planar backbones is about 3.6 Å 37 . The visualized images of molecular packing for three SMs ( Fig.…”

Electron Accepting Benzodithiophene-4,8-Dicarboxylate Designed for New Type D-A Narrow Bandgap Copolymers

“…2,6-Dibromo-4,8-benzodithiophenedicarboxylate (BDTC-Br 2 ) and 2-heptylthieno(3,4-d)thiazole were synthesized according to literature methods. [1,3] Synthesis of PBDTC-TTz. In a two-necked flask, BDTC-Br 2 (80.0 mg, 0.104 mmol), 2-heptylthieno(3,4-d)thiazole (24.7 mg, 0.104 mmol), dry THF (1.04 ml), tris(dibenzylideneacetone)dipalladium(0)-chloroform adduct (Pd 2 (dba) 3 CHCl 3 ) (5.38 mg), tris(2-methoxyphenyl)-phosphine (P(o-MeOPh) 3 (7.30 mg), pivalic acid (PivOH) (10.6 mg) and cesium carbonate (Cs 2 CO 3 ) (101.1 mg) were mixed with stirring at room temperature.…”

Emission from Charge-Transfer States in Bulk Heterojunction Organic Photovoltaic Cells Based on Ethylenedioxythiophene-Fluorene Polymers

“…Power conversion efficiency (PCE) of bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) has markedly improved in recent years [1][2][3][4][5]. The open-circuit voltage (V oc ) is one of the important parameters that determines the PCE.…”