Synthesis and characterization of light‐absorbing cyclopentadithiophene‐based donor–acceptor copolymers

Abstract

Cyclopentadithiophene and benzothiadiazole based donor–acceptor polymers are fast emerging as the most promising class of materials for organic solar cells. Here we report on a series of Cyclopentadithiophene and benzothiadiazole based conjugated polymers, namely poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole] (P1), poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐alt‐9‐(heptadecan‐9‐yl)‐2,7‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐9H‐carbazole] (P2) and poly[4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole‐alt‐5,11‐bis(2‐hexyldecyl)‐3,9‐bis(4,4,5,5‐tetramethyl)‐1,3,2‐dioxaborolan‐2‐yl)‐5,11‐dihydroindolo[3,2‐b]carbazole] (P3), with alternating donor and acceptor units and discuss their photophysical and electrochemical properties. Stille coupling of 2‐tributylstannyl‐4,4‐dioctylcyclopenta[2,1‐b:3,4‐b′]dithiophene with 4,7‐dibromobenzo[1,2,5]thiadiazole generated the alternating donor–acceptor monomer 4,7‐bis(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene‐2‐yl)benzo[1,2,5]thiadiazole (CPDT‐BT‐CPDT). Homopolymer P1 of CPDT‐BT‐CPDT was synthesized by oxidative polymerization using FeCl3. Copolymers P2 and P3 were synthesized by palladium‐catalysed Suzuki polycondensation. The synthesized polymers showed good solubility in common organic solvents, and UV‐visible measurements showed that the absorption maxima of the polymers lie in the range 624 to 670 nm. The energy gaps of these polymers were found to lie in the range 1.29 to 1.50 eV. Gel permeation chromatography measurements against polystyrene standards showed the number‐average molecular weight to be in the range (2.2–6.0) × 104 g mol−1. Thermogravimetric analysis showed the polymers to possess high thermal stability. A preliminary study of photodiode devices prepared using polymers P1, P2 and P3 when blended with the PC71BM electron acceptor found that P2 is the optimum chemical structure for pursuing further device optimization.© 2015 Society of Chemical Industry

Direct Arylation Strategies in the Synthesis of π-Extended Monomers for Organic Polymeric Solar Cells

“…The same author reported the synthesis of 3 via Suzuki coupling (60% yield) using Pd(PPh 3 ) 4 as catalyst system (30 mol %), commercial 2,1,3-Benzothiadiazole-4,7-bis(pinacol boronate ester) 5 and mono-brominated CPDT 6 , which had to be prepared via bromination reaction with N -bromosuccinimide (NBS) carried out on compound 1 . The synthesis of 3 could be achieved with Stille protocol [ 30 ] using 5 mol % of Pd(PPh 3 ) 4 but, in analogy with the Suzuki protocol, the synthesis of starting material 7 was needed. The procedure in Scheme 2 highlights a greater synthetic sustainability of DHA compared to Suzuki and Stille reactions in terms of reduction of synthetic steps, reaction time, E -factor (with reduction of wastes) and cost of reactions in spite of a yield decrease.…”

Effect of Co-monomers on Triphenylamine-Thiazolothiazole-Based Donor-Acceptor Copolymers: Synthesis and their Optical Properties

“…The outstanding performance of fullerene derivatives in polymer solar cells paves the way to focus design new p‐type semiconductor polymers with small band gaps, appropriate energy levels, strong and broad absorption with high charge carrier mobility to attain high efficiency in PSCs. Among the different strategies, donor‐acceptor (D−A) type polymers attract much attention due to the ability to manipulate the electronic structure through their partial intermolecular charge transfer . Recently, more than 10% power conversion efficiency was achieved by He et al .…”

Synthesis and evaluation of properties of poly(p‐phenylenevinylene) based 1,3,4‐oxadiazole systems for optoelectronics and nonlinear optical applications

“…π‐conjugated polymers are well known optoelectronic materials due to their bright luminescent properties, high thermal stability, excellent semiconducting ability, tunable highest occupied molecular orbital (HOMO) ‐ lowest unoccupied molecular orbital (LUMO) energy levels and high chemical inertness . Different π‐conjugated systems are now being extensively employed for the fabrication of organic field‐effect transistors, organic light‐emitting diodes (OLEDs), polymer solar cells and sensors …”