D‐A Polymer with a Donor Backbone ‐ Acceptor‐side‐chain Structure for Organic Solar Cells

Abstract

We report the design, synthesis, and properties of a novel type of donor (D)‐acceptor (A) polymer, poly(3‐(([2,2′:5′,2′′‐terthiophen]‐3‐yl‐5,5“‐diyl)methylene)‐1‐(2‐octyldodecyl)indolin‐2‐one) (PTIBT), with a donor backbone and acceptor side chains (Type II D‐A polymer) as donor for organic solar cells (OSCs) as opposed to the conventional D‐A polymers having both donor and acceptor units on backbone (Type I D‐A polymers). PTIBT having a backbone consisting of thiophene donor units and side chains containing indolin‐2‐one acceptor units was synthesized very conveniently in three steps. This polymer has a high dielectric constant of 7.70, which is beneficial for the exciton diffusion and dissociation in the active blend layer in an OSC. In addition, PTIBT was found to have a low‐lying HOMO energy level of −5.41 eV and a wide band gap of 1.80 eV in comparison to its counterpart Type I D‐A polymer. In organic thin film transistors (OTFTs), PTIBT showed typical p‐type semiconductor performance with hole mobilities of up to 1.81×10−2 cm2 V−1 s−1. When PTIBT and ITIC were used as donor and acceptor to form a blend active layer, the best OSC device showed a JSC of 15.19 mAcm−2, a VOC of 0.66 V, and a fill factor of 0.57, resulting in a power conversion efficiency (PCE) of up to 5.72%.

Wide Bandgap Polymer Donor with Acrylate Side Chains for Non‐Fullerene Acceptor‐Based Organic Solar Cells

“…2,5-Dibromothiophene-3-carbaldehyde (1) [20] and 2,5dibromothiophene-3-carboxylic acid (4) [34] were prepared according to literature procedures. 2,6-Bis(trimethytin)-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (6) was purchased from 1-Material.…”

“…[23] Therefore, much effort has been made to develop high dielectric organic semiconductors in order to extend the PCE limit of OSCs. [20,26,[30][31][32] Alkyl thiophene-3-carboxylate (TC), which can be easily prepared from thiophene-3-carboxylic acid by esterification, is a weak electron acceptor building block used for some high performance polymer donors. [22,[33][34][35][36] For example, Hou et al developed a polythiophene consisting of a dimer of 2-butyloctyl-thiophene-3-carboxylate, PDCBT, which achieved a high PCE of 10.16% when paired with ITIC.…”

“…[ 15 ] Another important factor, the synthesis cost of polymer donors, becomes more and more important when considering the commercialization of OSCs. [ 16–22 ]…”

Wide bandgap polymer donors for high efficiency non-fullerene acceptor based organic solar cells

“…Combined with lower recombination and higher exciton dissociation and charge collection efficiencies, devices based on PX1:ITIC showed largely improved PCE of up to 10.16% compared to the PCE of 1.25% for P3HT:ITIC, demonstrating the potential of polythiophenes for achieving high photovoltaic performance. Another strategy to improve the photovoltaic performance of polythiophenes is to design novel D-A polymer donors with conjugated D and A units located at backbone and side chains, respectively, which was demonstrated by He et al 165 with a polymer PX2 (PTIBT) that has an electron-rich polythiophene backbone and electron-accepting indolin-2-one side chains. The polymer with the so-called donor-backboneacceptor-side-chain structure showed a very high dielectric constant of 7.70 due to the largely separated donor and acceptor units, which is beneficial for the exciton diffusion to the donor:acceptor interface and subsequent dissociation into free electrons and holes.…”

Derivatives of diphenylamine and benzothiadiazole in optoelectronic applications: a review

“…Understanding the relationship between the structure and optoelectronic properties of organic semiconductors is essential when designing the architecture of the above-mentioned devices in order to achieve their optimal parameters, including high efficiency [17]. The most advantageous solution in optoelectronics design strategies is a "donor-acceptor" (D-A) or "push-pull" structural motif in organic semiconductors, due to the ability to control the band gap width [18][19][20]. So far, various groups of donors, acceptors, and π bridges have been combined in the research, e.g.…”