The increasing energy demand for diverse applications requires new types of devices and materials. Multifunctional materials that can fulfill different roles are of high interest as they can allow fabricating devices that can both convert and store energy. Herein, organic donor-acceptor redox polymers that can function as charge storage materials in batteries and as donor materials in bulk heterojunction (BHJ) photovoltaic devices are investigated. Based on its reversible redox chemistry, phenothiazine is used as the main building block in the conjugated copolymer design and combined with diketopyrrolopyrrol and benzothiadiazole as electron-poor comonomers to shift the optical absorption into the visible region. The resulting polymers show excellent cycling stability as positive electrode materials in lithium-organic batteries at discharge potentials of 3.6-3.7 V versus Li/Li+ as well as good performances in BHJ solar cells with up to 1.9% power conversion efficiency. This study shows that the design of such multifunctional materials is possible, however, that it also faces challenges, as essential properties for good device function can lead to diametrically opposite requirements in materials design.

Organic electrode materials are considered to bepromising candidates for alternative and greener energy storagesolutions. Due to their intrinsic low conductivity, however, usuallylarge amounts of conductive additives are required for electrodefabrication. Herein, we investigate electrodes with a 90 wt % activematerial ratio and high mass loadings of up to 4.3 mg cm-2, whichshow good cycling performance because of the conjugatedcopolymer structure chosen for the phenothiazine-based activematerial. By furthermore reducing the inactive weight within thepolymer through structural modification and raising the potentialrange during constant current measurements we increased thedischarge capacity for the whole composite by a factor of 12 to0.169 mAh cm-2compared to a previous study. This studydemonstrates that conjugated organic copolymers are attractive electrode materials due to their intrinsic conductivity combined withthe presence of defined redox centers.

Azine-based polymers as cathode-active materials with a two-electron redox process show a high specific capacity of up to 133 mA h g−1 in Li–organic batteries at potentials of 2.9 and 3.3 V vs. Li/Li+ paired with a high rate performance up to 100C.

In recent years, organic battery cathode materials have emerged as an attractive alternative to metal oxide–based cathodes. Organic redox polymers that can be reversibly oxidized are particularly promising. A drawback, however, often is their limited cycling stability and rate performance in a high voltage range of more than 3.4 V versus Li/Li + . Herein, a conjugated copolymer design with phenothiazine as a redox‐active group and a bithiophene co‐monomer is presented, enabling ultra‐high rate capability and cycling stability. After 30 000 cycles at a 100C rate, >97% of the initial capacity is retained. The composite electrodes feature defined discharge potentials at 3.6 V versus Li/Li + due to the presence of separated phenothiazine redox centers. The semiconducting nature of the polymer allows for fast charge transport in the composite electrode at a high mass loading of 60 wt%. A comparison with three structurally related polymers demonstrates that changing the size, amount, or nature of the side groups leads to a reduced cell performance. This conjugated copolymer design can be used in the development of advanced redox polymers for batteries.