Side chain engineering and conjugation enhancement of benzodithiophene and phenanthrenequnioxaline based conjugated polymers for photovoltaic devices

Abstract

A series of donor-acceptor conjugated polymers incorporating benzodithiophene (BDT) as donor unit and phenanthrenequnioxaline as acceptor unit with different side chains have been designed and synthesized. For polymer P1 featuring the BDT unit and alkoxy chains substituted phenanthrenequnioxaline unit in the backbone, serious steric hindrance resulted in quite low molecular weight. The implementation of thiophene ring spacer in polymer P2 greatly suppressed the interannular twisting to extend the effective conjugation length and consequently gave rise to improved absorption property and device performance. In addition, utilizing the alkylthienyl side chains to replace the alkyl side chains at BDT unit in polymer P3 further enhanced the photovoltaic performance due to the increased conjugation length. For polymer P4, translating the alkoxy side chains at the phenanthrenequnioxaline ring into the alkyl side chains at thiophene linker group enhanced molecular planarity and strengthened p2p stacking. Consequently improved absorption property and increased hole mobility were achieved for polymer P4. Our results indicated that side chain engineering not only can influence the solubility of polymer but also can determine the polymer backbone planarity and hence the photovoltaic properties.

Comprehensive study of pyrido[3,4‐b]pyrazine‐based D–π–a copolymer for efficient polymer solar cells

“…The LUMO levels were then calculated from the differences between the HOMO energy level and the optical bandgaps. Figure 3(b) depicts a sketch of the energy levels for PBDT-TBQ, PBDT-TPQ, and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM). PBDT-TPQ exhibits a relatively lowerlying HOMO energy level at 25.24 eV, which is in an ideal range to ensure better air stability and can be anticipated to produce a higher open-circuit voltage (V oc ), in accordance with the known linear correlation of V oc with the difference between the HOMO energy level of a donor and the LUMO energy level of an acceptor.…”

“…It has been recognized that an ideal polymer donor in OPVs should represent broader absorption with high absorption coefficient in the visible and near‐infrared region, high hole mobility, and suitable electronic energy levels matching the fullerene acceptor . In this regard, the combination of alternating electron‐rich donor (D) and electron‐deficient acceptor (A) moieties along the backbone is a powerful strategy in designing narrow bandgap conjugated polymer with broad absorbance . Thus, seeking novel efficient donor and acceptor units to develop well‐performed p‐type conjugated polymers is of great significance in BHJ solar cells.…”

Medium‐Bandgap Conjugated Polymer Donors for Organic Photovoltaics

“…Besides 2,3‐diphenylquinoxaline‐based polymers (like P97 and P98), phenathrene‐quinoxaline based D–A conjugated polymers have also attracted much attention as electron‐accepting building blocks because of the more fused structure and extended conjugation length, leading to higher planarity and better intermolecular packing. Two D–A conjugated polymers P102 and P103, combining a BDT donor unit and alkoxyl chains substituted phenathrenequinoxaline unit, respectively, were synthesized by Sun and co‐workers . Compared to P103, the introduction of alkylthienyl on the BDT unit not only increased the effective conjugated length but also enhanced the photovoltaic performance of the resulting conjugated polymer P102.…”

Engineering the self-assembly of diketopyrrolopyrrole-based molecular semiconductors via an aliphatic linker strategy

“…In contrast, routes for controlling molecular self-assembly by engineering the solubilizing side chains can preserve the electronics of the semiconducting core. 31 This route has been widely investigated for π-conjugated polymers, [32][33][34][35][36][37][38] and to lesser extent for small molecule organic semiconductors. [39][40][41][42] Indeed, since the selfassembly of a typical molecular semiconductor with standard aliphatic solubilizing chains is dominated by π-π interactions, side chain engineering offers limited control.…”