Toward High Efficiency Polymer Solar Cells: Rearranging the Backbone Units into a Readily Accessible Random Tetrapolymer

Abstract

Two donor–acceptor (D–A) conjugated polymers composed of the same ratio of 5‐fluorobenzothiadiazole and thiophene subunits are synthesized through different routes, providing a precisely regioregular (2TRR) and a random (2TRA) polymer structures. Detailed structural analyses indicate that the backbone of regioregular 2TRR has only one donor segment of bithiophene, while the backbone of random 2TRA consists of three different donor segments: thiophene, bithiophene, and terthiophene (in a ratio of 0.16:0.68:0.16). Synergetic contributions from these segments allow the “tetrapolymer” 2TRA to achieve more favorable film morphology and a higher hole‐mobility relative to 2TRR. Consequently, the random polymer 2TRA achieves a substantially higher power conversion efficiency (8.8%) than the regioregular polymer 2TRR (5.1%). Notably, the “tetrapolymer” 2TRA is readily synthesized from two monomers, rather than through complex conventional preparation required for similar multipolymers. These findings provide a novel route toward the design and synthesis of multipolymeric materials and demonstrate their potential advantages in high‐performance organic electronic applications.

Unraveling the Effect of Conformational and Electronic Disorder in the Charge Transport Processes of Semiconducting Polymers

“…Although our theoretical model has currently only been resolved for P3HT, future work will expand the model to encompass donor–acceptor (D–A) materials, enabling the effect of polaron localization in donor–acceptor materials to be studied. Combining our polaron studies with previous work studying charge transport in D–A materials will allow us to determine if these materials are limited by the same mechanisms as P3HT as shown in this work, and if P3HT can truly act as a representative model system. Our work thus demonstrates that an understanding of the fundamental processes that control charge transport in conjugated polymers is crucial in selecting the appropriate characterization techniques needed to connect microstructure to transport.…”

Chlorination strategy on polymer donors toward efficient solar conversions

“…Benzothiadiazole (BT) as an electron-deficient unit is perhaps the most popular acceptor moiety for D − A -type copolymers used in polymer solar cells. Here, the chlorinated strategy is also an effective method to finely tune the HOMO energy levels in BT unit involved polymer solar cells [75] . In 2017, the chlorinated benzothiadiazole had been copolymerized with benzo[1,2b :4, b ]dithiophene (BDT) by our group, to obtain four chlorinated polymers with the different alkyl chains, namely, PBDTHD-ClBTDD, PBDTBO -ClBTDD, PBDTHD-ClBTEH and PBDTBO -ClBTEH ( Chart 1 ).…”

Influence of Regioregularity on the Optoelectronic Properties of Conjugated Diketopyrrolopyrrole Polymers Comprising Asymmetric Monomers

“… 25 − 35 However, a recent comparison between regiorandom and regioregular 5-fluoro-2,1,3-benzothiadiazole (FBT) polymers questions the superior design of regioregular polymers since the regiorandom polymer in these studies had a higher hole mobility 36 , 37 and significantly improved performance in polymer solar cells. 37 Another class of asymmetric D–A polymers for which regioregularity control of the backbone is important are based on thieno[3,4- b ]thiophene (TT). By synthesizing a regioregular PBDTTT-C-T polymer based on alternating benzo[1,2- b :4,5- b ′]dithiophene (BDT) with perfectly controlled TT orientation, Lee et al 38 showed that the regioregular polymer has a higher degree of crystallinity, a higher charge carrier mobility, and improved photovoltaic performance compared to the regiorandom isomer.…”