Contrasting Effect of Alkylation on the Ordering Structure in Isomeric Naphthodithiophene-Based Polymers

Abstract

Semiconducting polymers with alkylated naphtho [1,2b:5,6-b′]dithiophene (NDT3) and naphtho[2,1-b:6,5-b′]dithiophene (NDT4) are synthesized and characterized. The solubility of the present polymers is significantly improved as compared to the nonalkylated counterparts with preserving the good charge transport properties. Interestingly, the effect of alkylation is found to be quite distinct between the NDT3 and NDT4 cores. In the NDT3-based polymers, alkylation leads to the more ordered backbone structure and thus the increased crystalline order in the thin film. On the other hand, in the NDT4-based polymers, alkylation is detriment to the backbone ordering, which gives rise to the face-on orientation or amorphous like film structure. This difference can be qualitatively explained by the different alkyl placement; all the neighboring alkyl groups are in the anti arrangement in the NDT3-based polymers, whereas the arrangement is a mixture of anti and syn in the NDT4-based polymers, which likely causes steric impact on the backbone. These observations make us better understood how the alkylation affect the ordering structures, which would be an important guideline for the design of superior semiconducting polymers.

Dependence of Crystallite Formation and Preferential Backbone Orientations on the Side Chain Pattern in PBDTTPD Polymers

“…While preferential "edge-on" orientations may favor in-plane carrier transport in thin-film FETs, 8 predominantly "face-on" polymer orientations have been suggested to promote BHJ solar cell efficiency. 1,7,17,29,30 Our results further emphasize the need to select the proper combination of side chains when several types of substituents are appended along the polymer backbone. Although branched alkyl substituents have been widely used to induce the solution-processability of π-conjugated polymers, motifs bearing linear side chains may also prove critical to the development of structural order in other systems analogous to PBDTTPD.…”

“…Although the material design principles at the origin of preferential backbone orientation in thin films, independent of processing conditions and substrate effects, remain under debate, our results shed light on the critical role and concurrent effects of the combination of side chains appended to the polymer main chain (Figure 1, R 1 and R 2 ) in the development of oriented crystallites. It is worth noting that the presence of oriented crystallites in polymer FETs 25−28 and across the active layer of BHJ solar cells 1,7,17,29,30 is often thought to contribute to improved carrier transport and device efficiency. Along these lines, the ability to mediate π−π aggregation and polymer crystallite orientation in thin films through material design can be expected to help improve material performance in both FETs and BHJ solar cells.…”

Benzothiadiazole and its π-extended, heteroannulated derivatives: useful acceptor building blocks for high-performance donor–acceptor polymers in organic electronics

“…In order to realize p-type and/or n-type unipolar polymers, our next approach was the simple, yet effective, heteroatom substitution on the BBT core. e For PDI-BDTT and PDI-BDTO, the solar cells were fabricated with a conventional device configuration using PC 71 BM as the electron acceptor materials; for BDTI-1 and BDTI-2, the solar cells were fabricated with an inverted OPV device architecture using PC 71 BM as the electron acceptor materials. The effects of the heteroatom substitution was clearly observed on the energy levels of these polymers, determined from cyclic voltammetry (CV) measurements.…”

“…Second, by 35 varying the substitution positions and density of the alkyl chains, P5 and P6 were synthesized to improve the solubility. 68,71,72,74 polymers M n (kg mol -1 ) Taking this result into account, P6 with a pair of 2- Table 4 NTz-based polymer structures, molecular weights, optical absorption, energy levels, OPV and OFET properties.…”

Naphthodithiophenes: Emerging Building Blocks for Organic Electronics

“…For example, PCEs higher than 5% were reported for the P15 and P19 PC 71 BM‐based OPVs by Li and co‐workers. Although the alkyl‐substituted NDT3 unit has not yet been fully exploited as the D unit in semiconducting polymers, P20 consisting of the 5,10‐dialkylated NDT3 and NTz units can afford OPVs with impressively high PCEs of up to 8.2% with PC 71 BM and 7.5% with PC 61 BM, which are among the highest for OPVs based on recently developed new semiconducting polymers . The characteristic feature of these OPVs is that the active BHJ layer has a relatively high crystallinity, which, in combination with the favorable face‐on polymer orientation, facilitates transport of generated charges, resulting in higher PCEs (Figure ).…”