The Renaissance of Oligothiophene‐Based Donor–Acceptor Polymers in Organic Solar Cells

Abstract

The power conversion efficiencies (PCEs) of OSCs have reached 19% as the innovation of state-of-the-art nonfullerene acceptors. [2] On the contrary, the development of polymer donors lags much behind. Up to date, the polymer donors are limited to a handful of polymers and, more specifically, thiophene-substituted benzo [1,2-b:4,5-b']dithiophene (BDTT) polymers. [3] The side-chain conjugated substituents on BDTT could extend backbone conjugation and electron delocalization, enhance interchain π-π interaction, and improve charge transport of the polymers. Moreover, the absorption spectra, energy levels, and crystallinity of BDTTbased polymer donors can be finely tuned by both main-chain and side-chain engineering. [4] As a result, these kinds of polymers, such as PM6 and D18 (Figure 1a), [5] perform well in both fullerene and nonfullerene OSCs. [3a,4] However, BDTT-based polymers usually suffer from lengthy synthesis and tedious purification processes, which inevitably result in a high production cost and bring difficulties for the large scale synthesis. [6] Therefore, high-performance polymer donors with simple structure and facile synthesis are urgently needed to drive the further development of OSCs. [7] Among various polymer donors, poly(3-hexylthiophene) (P3HT) is one of the most extensively studied polymers due to its simple structure, low production cost, good self-assembly property, and high charge transport ability. [8] However, the PCEs of P3HT-based OSCs were restrained at about 10% due to the high-lying HOMO level of P3HT and excessively mixed active layer morphology. [9] An alternative strategy is incorporating electron-deficient units into the polymer main chain to form oligothiophene-based donor-acceptor polymers. This kind of polymer employs oligothiophene as a donor unit and thus the properties of the polymers can be adjusted by both the oligothiophene unit and acceptor unit. Moreover, these kinds of polymers can be synthesized more easily than BDTTbased donor-acceptor polymers. [10] A few state-of-the-art oligothiophene-based polymer donors such as PffBT4T-2OD and PNTT [11] (Figure 1a) have been developed, which exhibited good crystallinity and high hole mobility. Moreover, this kind of polymers usually exhibits temperature-dependent aggregation properties, which have provided valuable opportunities to regulate The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have increased rapidly owing to the development of non-fullerene acceptors (NFAs). However, the development of polymer donors lags behind significantly. Currently, the polymer donors are dominated by a handful of thiophenesubstituted benzo[1,2-b:4,5-b']dithiophene (BDTT) polymers, which suffer from lengthy synthesis and high production cost. Compared with BDTT-based polymers, oligothiophene-based donor-acceptor polymers feature much easier synthesis, which were the prevailing polymer donors in fullerene-based OSCs, but almost disappeared in non-fullerene OSCs. Herein, two oligothiophene-based donor-acceptor pol...

The Key Role of Subtle Substitution for a High‐Performance Ester‐Modified Oligothiophene‐Based Polymer Used in Photovoltaic Cells

“…[ 10‐11,15‐17 ] Moreover, reducing the synthetic complexity of donor polymer is essential for future mass production. [ 18‐22 ] Therefore, the molecular design of donor polymers with both well‐matched properties and simple synthetic routes is of critical importance but remains a challenging task in fullerene‐free OSCs.…”

A structurally simple linear conjugated polymer toward practical application of organic solar cells

“…1b), based on thiazolothiazole (TzTz) and terthiophene has been demonstrated, which can afford comparable short circuit current density ( J sc ) and fill factor (FF) with state-of-the-art BDTT-based conjugated polymers. 44 The major drawback of PTTz-3HD is the shallow highest occupied molecular orbital (HOMO) energy level (−5.36 eV), which resulted in a low open circuit voltage ( V oc ) in OSCs. Herein, we report a new linear conjugated polymer PTTzF (Fig.…”

Three Isomeric Non-Fullerene Acceptors Comprising a Mono-Brominated End-Group for Efficient Organic Solar Cells

“…Therefore, this work provides a facile and unique method (one reaction and one column chromatography) to achieve all three NFA isomers with a mono-halogenated IC end-group. Low-cost photovoltaic materials, particularly for the polymer donors ,− and NFAs, ,, are in great demand due to the commercialization of OSCs, and polymer donors with a thiophene-dominated backbone are prominent . Herein, benzodithiophene (BDT)-free PFBT4T-T20 (Figure S3) was selected as the easily accessible and low-cost polymer donor to evaluate the photovoltaic performances of three isomeric NFAs.…”

“…The best efficiency of 16.00% achieved with isomer BTzIC-2Br-γ is among the highest ones for binary OSCs based on BDT-free low-cost donors (Table S1). ,, …”