Fine Control of Side Chains in Random π‐Conjugated Terpolymers for Organic Photovoltaics

Abstract

Rational molecular design of π‐conjugated donor polymers is critical for developing high‐performance organic solar cells. Random copolymerization strategy is a facile method of synergistic fine‐tuning the light absorption, HOMO/LUMO energy levels, charge mobility, and solubility of donor (D)–acceptor (A) copolymers. Terpolymers PF8TBT which composed of three components, i.e., electron‐rich 9,9‐dioctylfluorene (F8), electron‐deficient benzothiadiazole (BT), and π‐bridge thiophene (T) moieties, are designed in such a way that only F8 unit possesses soluble side‐chains. This strategy enables a facile and precise control of the influences of side chains on solubility, energy levels, molecular packing, and fullerene (PCBM) intercalation of PF8TBT. The optimal terpolymer PF8TBT21 (F8:T:BT = 0.67:1:0.33 mol%) maximally balances the solubility and the PL quenching efficiency with PCBM while exhibiting notable π–π stacking. The resulting additive‐free inverted photovoltaic cell based on the PF8TBT21:PCBM blend shows a power conversion efficiency of 3.88% with an impressive open‐circuit voltage close to 1 V.

Synthesis and photovoltaic device studies of azo‐linked low‐bandgap polymers

“…The fluorene‐based polymers have been reported for their processability, high hole mobility and PL efficiency . The miscibility and film morphology of polymers with C71‐PCBM are usually characterized by the PL quenching efficiency ( ϕ q ) as calculated by ϕ q = ( I 0 − I )/ I 0 , where I 0 is the PL intensity of polymer film and I is the PL intensity of polymer:C71‐PCBM blend film . We therefore investigated the ϕ q value of P5 :C71‐PCBM and find that it is 16% higher than that of P6 :C71‐PCBM blend, which shows good intermixing of P5 polymer with C71‐PCBM.…”

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.…”

Enhancing the Performance of Polymer Solar Cells by Using Donor Polymers Carrying Discretely Distributed Side Chains

“…For most donor–acceptor-type conjugated polymers, the flexible side chains are homogeneously located at the polymer main chain. − The design and synthesis of terpolymers for some systems was proven to be efficient in challenging the balance of solubility and photovoltaic properties . In addition, synthetic workload of this type of polymers will be reduced rapidly, and favorable properties arise . By the introduction of a third component, the side chains will be discretely distributed in the polymer main chain, which will be expected to enhance the “cross-talking” between polymer chains, leading to improved hole-transport ability and device performance.…”

“…37 In addition, synthetic workload of this type of polymers will be reduced rapidly, and favorable properties arise. 38 By the introduction of a third component, the side chains will be discretely distributed in the polymer main chain, 39 which will be expected to enhance the "cross-talking" between polymer chains, leading to improved hole-transport ability and device performance. To verify the feasibility of this idea, we synthesized a kind of three-component conjugated polymers consisting of thiophene, 5-fluoro-6-alkyloxybenzothiadiazole, and 5,6-difluorobenzothiadiazole.…”