Exploring the influence of acceptor content on semi‐random conjugated polymers

Abstract

A family of diketopyrrolopyrrole (DPP)‐incorporated P3HT based semi‐random copolymers was synthesized and their optical, electronic and photovoltaic properties were investigated. For the first time, the influence of acceptor content on semi‐random copolymers was explored in the broad range of 10–40% acceptor. A mixture of DPP acceptor units with different side chains (ethylhexyl and decyltetradecyl) was incorporated into each copolymer to improve solubility and film quality. Increased DPP content in the polymer backbone resulted in broadened absorption between 350 and 900 nm, resulting in a monotonic decrease in optical band gap (Eg) of the polymers from 1.49 to 1.37 eV. Highest occupied molecular orbital (HOMO) energy levels showed an increase from 10% DPP to 20–30% DPP, while decreasing for 40% DPP. Voc values followed a consistent trend with HOMO energy levels. Semi‐random copolymers showed significantly improved photovoltaic properties compared with P3HT. Bulk heterojunction solar cells fabricated from the semi‐random copolymers blended with PC61BM exhibited high short‐circuit current densities (Jsc) up to 10.29 mA/cm2 and efficiencies up to 4.43%. A new method of methanol treatment was developed and applied to the semi‐random copolymers resulting in high fill factors approaching 0.70 under ambient conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3884–3892

Influence of Acceptor Side-Chain Length and Conjugation-Break Spacer Content on the Mechanical and Electronic Properties of Semi-Random Polymers

“…Within the T-8-T/dtdDPP subfamily, a trend appeared in the as-cast films in which the lamellar packing distance decreased with increasing CBS and dtdDPP incorporation. Although the fraction of monomer with long side-chains was increasing within this data set, it seemed that increasing the CBS content allowed the polymer chains to pack closer together, likely due to the enhanced open space provided by the increased fraction of CBS, and counter to the trend observed by Ekiz et al when increasing DPP content without the use of a CBS monomer . Interestingly, there is no observed diffraction peak for the fully conjugated polymer before annealing.…”

“…The 100 diffraction peaks for as-cast films corresponded to a lamellar packing distance of 17.3–20.4 Å, larger than the range of 15.6–16.5 Å observed in our original study for ehDPP analogues. This can be explained by the longer DPP side-chains generally causing the polymer chains to pack further apart, a phenomenon previously observed in our group when exchanging ethylhexyl side-chains for decyltetradecyl side-chains . Within the T-8-T/dtdDPP subfamily, a trend appeared in the as-cast films in which the lamellar packing distance decreased with increasing CBS and dtdDPP incorporation.…”

Sequence-Controlled Electron Transport in Conjugated Copolymers

“…Third, as the computational framework constructed here maps directly onto the framework for statistical copolymerization, one could employ this methodology to make predictions on recently developed classes of statistical conjugated copolymers. − Traditional ab initio methods for characterizing electronic structure are limited by both the required length scales of sequence correlations (10–100 monomers) and the computational challenge of sampling the full-sequence ensemble. The phenomenological nature of the transport models used in this work combined with the statistical sampling intrinsic to the Markov chain procedure provides a means for fully accounting for the sequence complexity of conjugated copolymers with substantially reduced computational cost.…”

“…In the 2000s, conjugated homopolymers such as P3HT and MEH-PPV were surpassed in many applications by the introduction of alternating “donor–acceptor” (DA) copolymers, enabling polymers with lower band gaps and improved electronic mobilities. , These leaps in performance were followed by the exploration of other DA copolymer architectures including large fused π-systems, , as well as fully conjugated rod–rod block copolymers . Within the past decade, numerous sequence design strategies have been developed involving statistical copolymerization − and gradient − architectures, facilitating a broad range of optoelectronic properties and new schemes for tailoring conjugated copolymer functions. These synthetic advances motivate the need for a theoretical framework capable of guiding sequence design in conjugated copolymers via rapid electronic property predictions that account for sequence correlations spanning the full-chain contour length.…”

Ternalization Approach for Tuning Light Absorption and Crystalline Structure of Diketopyrrolopyrrole-Based Polymer Using Bisthiadiazole Unit

“…Random or semi-random copolymers that contain several different units in the polymer backbone can overcome this drawback. 11,12 Since different light absorbers are chemically bonded with continual conjugation, a wide wavelength of light can be absorbed by a single polymer film. Moreover, the third component gives additional freedom in the polymer chain packing and solubility.…”