The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells

Abstract

A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure.

Preparation of semi‐alternating conjugated polymers using direct arylation polymerization (DArP) and improvement of photovoltaic device performance through structural variation

“…In general, P5 – P8 possess absorbance profiles extending from approximately 500–850 nm. For the polymers P7 and P8 , the profile and values for λ abs are similar to what has been reported previously . A large redshift (100 nm) is observed from P5 to P8 .…”

“…The location for donor homocouplings are indicated by the symbol, δ at 7.10 ppm, those of the acceptors, both DTTPD and DTDPP, are indicated by the symbol, α 2 at 7.85 and α 1 at 9.23 ppm, respectively, and end‐groups are indicated with an asterisk. The PPDTDPP polymers ( P5 – P8 ) all provided proton NMR spectra with well‐defined resonances identical to the PPDTDPP polymers reported in literature, but the PPDTTPD polymers ( P1 – P4) provided relatively featureless aromatic regions . However, the semi‐alternating polymer PPDTDPPTPD, P9 , provided relatively well defined resonances allowing for the analyses for all potential homocoupling defects, and this is the spectrum provided in Figure .…”

“…A four‐component randomized polymer incorporating two different phenylene donors and both DTTPD and DTDPP was prepared to show that the used DArP conditions can lead to more complex polymers without the observance of structural defects. While PPDTDPP‐based polymers have been prepared using DArP and Suzuki methods previously, the previous materials prepared using DArP were not characterized in solar cell devices …”

The synthesis and purification of amphiphilic conjugated donor–acceptor block copolymers

“…The addition of solubilizing hexyl side chains in the PF TEG T6BT material leads to a blue shift in absorption, a result of increased steric bulk disrupting the planarity of the conjugated backbone and decreasing the effective conjugation length. 36 An increase in absorption at 450 nm is seen in both BCPs indicating a contribution from the P3HT block. The P3HT absorption is more pronounced in the P3HT-b-PF TEG T6BT materials, a function of the Amphiphilic conjugated donor-acceptor BCP VD Mitchell et al decreased absorption coefficient of the acceptor material resulting from the additional side chains.…”

Effects of o-Methoxy Groups on the Properties and Thermal Stability of Renewable High-Temperature Cyanate Ester Resins

“…This abundant biofeedstock is currently generated by the commercial paper industry and is a significant component of forestry residue and agricultural waste. Crude forms of lignin can be acquired for ∼$0.05/lb, and it is estimated that as many as 250 million tons could be sustainably produced annually in the US by 2030. , Despite the promise of lignin-derived and other natural phenols, these molecules typically contain additional functional groups (primarily methoxy groups) that can affect the material properties, thermal stability, and decomposition pathways of derivative thermoplastics and thermosetting resins. − …”