Design of Random and Semi‐Random Conjugated Polymers for Organic Solar Cells

Abstract

Significant effort has been devoted to the improvement of organic solar cell performance via the optimization of polymer structure. The expanding scope of conjugated polymer design extends from novel monomers to side‐chain and backbone engineering. These efforts target desired properties for optimal organic photovoltaic performance, including electronic aspects such as optical band gaps, frontier orbital levels, and charge carrier mobilities, as well as physical aspects such as surface energy. Perfectly alternating, donor‐acceptor copolymers represent the state‐of‐the‐art, having low band gaps and demonstrating record efficiencies. However, recent reports indicate significant potential by introducing some degree of randomization to donor‐acceptor copolymers. Specifically, semi‐random copolymers have demonstrated promising photovoltaic performance through incorporation of small ratios of acceptor monomers into a donor‐dominant polymer backbone. Semi‐random polymers have also been found uniquely suited to the optimization of ternary blend solar cells, which benefit from highly tunable randomized structures by means of energy level matching, complementary optical absorption, and directed polymer‐polymer miscibility via surface energy tuning. In this trend article the scope of random and semi‐random polymers, many based on poly(3‐hexyl thiophene), is explored, primarily in the context of solar cell applications. Distinctions between regimes of random copolymers are also defined and discussed.

Sequence-Controlled Electron Transport in Conjugated Copolymers

“…In the 2000s, conjugated homopolymers such as P3HT and MEH-PPV were surpassed in many applications by the introduction of alternating “donor–acceptor” (DA) copolymers, enabling polymers with lower band gaps and improved electronic mobilities. , These leaps in performance were followed by the exploration of other DA copolymer architectures including large fused π-systems, , as well as fully conjugated rod–rod block copolymers . Within the past decade, numerous sequence design strategies have been developed involving statistical copolymerization − and gradient − architectures, facilitating a broad range of optoelectronic properties and new schemes for tailoring conjugated copolymer functions. These synthetic advances motivate the need for a theoretical framework capable of guiding sequence design in conjugated copolymers via rapid electronic property predictions that account for sequence correlations spanning the full-chain contour length.…”

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Conjugated Polymers for Nonfullerene Organic Solar Cells

“…Being a facile method of tuning optoelectronic properties, random polymerization has emerged as an important approach for synthesizing new polymeric materials as donors and acceptor materials in the application of OSCs. [69][70][71][72] The chemical structures of TPD-based random conjugated polymers are illustrated in Figure 4 and the photovoltaic properties are summarized in Table 4. Kim et al synthesized a set of random polymers with different feed ratios.…”

Effect of Third Component on Efficiency and Stability in Ternary Organic Solar Cells: More than a Simple Superposition

“…As first proposed by Thompson and co‐workers, the alloy model requires that the third components and one of the host materials are electronically coupled to form a new independent charge carrier transport network with new HOMO and LUMO energy levels. [ 85 ] Unlike the parallel‐linkage model, in the alloy model, the third component is required to be extremely miscible with the host materials to form an alloy state. As shown in Figure 8d, in the device with a D 1 /D 2 /A structure, the alloy with D 1 and D 2 adopts a new energy level depending on the mixing ratio of the two donors.…”