Synthesis of thiophene-based π-conjugated polymers containing oxadiazole or thiadiazole moieties and their application to organic photovoltaics
Journal
Macromolecules
Journal Volume
45
Journal Issue
22
Pages
9046-9055
Date Issued
2012
Author(s)
Abstract
We report the synthesis, properties, and photovoltaic applications of new π-conjugated polymers having thiophene, 3,4-dihexylthiophene, and 1,3,4-oxadiazole (OXD) or 1,3,4-thiadiazole (TD) units in the main chain, denoted as P1 and P2. They were synthesized by the Stille coupling reaction of 2,5-bis(trimethylstannyl)thiophene and the corresponding monomers of 2,5-bis(5′-bromo-3′,4′-dihexylthien-2′-yl)-1,3, 4-oxadiazole or 2,5-bis(5′-bromo-3′,4′-dihexylthien-2′- yl)-1,3,4-thiadiazole, respectively. The experimental results indicated that the introduction of an electron-accepting moiety of OXD or TD lowered the highest occupied molecular orbital (HOMO) energy levels, resulting in the higher the open-circuit voltage (Voc) values of polymer solar cells (PSCs). Indeed, the PSCs of P1 and P2 showed high Voc values in the range 0.80-0.90 V. The highest field-effect transistor (FET) mobilities of P1 and P2 with the OXD and TD moieties, respectively, were 1.41 × 10-3 and 8.81 × 10-2 cm2 V-1 s-1. The higher mobility of P2 was related to its orderly nanofibrillar structure, as evidenced from the TEM images. Moreover, the higher absorption coefficient and smaller band gap of P2 provided a more efficient light-harvesting ability. The power conversion efficiency (PCE) of the PSC based on P2:PCBM = 1:1 (w/w) reached 3.04% with a short-circuit current density (Jsc) value of 6.60 mA/cm2, a Voc value of 0.80 V, and a fill factor (FF) value of 0.576 during the illumination of AM 1.5, 100 mW/cm2. In comparison, the parent PDHBT without the electron-accepting moiety exhibited an inferior device performance (FET mobility = 2.10 × 10-4 cm 2 V-1 s-1 and PCE = 1.91%). The experimental results demonstrated that incorporating the electron-acceptor moiety into the polythiophene backbone could enhance the device performance due to the low-lying HOMO levels, compact packing structure, and high charge carrier mobility. This is the first report for the achievement of PCE > 3% using PSCs based on polythiophenes having TD units in the main chain. © 2012 American Chemical Society.
SDGs
Other Subjects
1 , 3 , 4-oxadiazole; 1 ,3 ,4-thiadiazole; Absorption coefficients; Compact packing; Device performance; Electron-accepting moieties; Electron-acceptor; Fill factor; Highest occupied molecular orbital energy levels; Light-harvesting; Main chains; Nanofibrillar; Organic photovoltaics; Oxadiazoles; Photovoltaic applications; Poly-thiophene; Polymer Solar Cells; Power conversion efficiencies; Stille coupling reaction; TEM images; Thiadiazoles; Conjugated polymers; Conversion efficiency; Electron energy levels; Field effect transistors; Open circuit voltage; Organic compounds; Solar cells; Thiophene
Type
journal article