Phenothiazine‐Based Donor–Acceptor Polymers as Multifunctional Materials for Charge Storage and Solar Energy Conversion

Abstract

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.

From Squaric Acid Amides (SQAs) to Quinoxaline-Based SQAs─Evolution of a Redox-Active Cathode Material for Organic Polymer Batteries

“… − Embedding small redox active molecules into polymeric frameworks disfavors migration processes between the electrodes and enables an easier material processing . Among the most prominent and thoroughly investigated ROMs are polymeric nitroxide radicals such as poly­(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA) − or poly­(galvinoxyl-styrene). , However, other ROMs have also been successfully turned into polymer cathode materials such as phenazines, − phenothiazines/oxazines, − dimethoxybenzenes, and cyclopropenium salts …”

Conjugated Nanohoop Polymers based on Antiaromatic Dibenzopentalenes for Charge Storage in Organic Batteries

“…To synthesize nanohoop‐based polymers, we chose three electronically diverse comonomer units: a dithienyldiketo(pyrrolopyrrol) (DTDPP) (electron‐poor), a fluorene (electronically “neutral”) and a carbazole (electron‐rich). These were employed in the form of their respective bis(boronic esters) 6 , 7 and 8 in order to perform Suzuki–Miyaura polycondensation reactions [40,41] . These polymerizations successfully furnished the nanohoop polymers P1 , P2 , and P3 in good yields of 46–51 %.…”

“…These were employed in the form of their respective bis(boronic esters) 6, 7 and 8 in order to perform Suzuki-Miyaura polycondensation reactions. [40,41] These polymerizations successfully furnished the nanohoop polymers P1, P2, and P3 in good yields of 46-51 %. Analysis by analytical gel-permeation chromatography confirmed the formation of polymers with average molecular weights of M w = 6,570-19,600 g mol À 1 and with low polydispersity indexes (see exact values in the table in Scheme 1).…”

Unlocking twofold oxidation in phenothiazine polymers for application in symmetric all-organic anionic batteries

“…2,3 In contrast, batteries in which the electrode materials are organic in nature do not rely on critical resources, while also being easier to recycle, which makes them a much more environmentally friendly alternative. Even more importantly, organic batteries offer unique advantages in terms of their ability to have their properties fine-tuned by structural design to achieve superior features such as fast charging rate performance, 4 adaptability to special applications 5,6 or to tailor their redox potentials. 7,8 The latter cannot only be exploited to develop a large variety of either positive or negative electrode materials, but careful selection of the organic moieties in the active material(s) has also enabled researchers to establish battery cells based on two organic electrodes, so-called 'all-organic' full-cells.…”

“…It features a stable and reversible oxidation, a high voltage vs. Li/Li + and high specific capacity (3.5 V vs. Li/Li + and 125.7 mAh g −1 per electron, for N-methyl phenothiazine), which is accompanied by the synthetic possibility to incorporate PT into different motifs. 4,5,24,[32][33][34][35][36][37] Furthermore, PT is generally capable of two singleelectron oxidations from its neutral form to a radical cation and further to a dication (Figure 1). The two processes are observed at high potentials of 3.5 V 38,39 and 4.2 V vs. Li/Li + (approximation based on the redox potential of the second oxidation of N-ethylphenothiazine (0.93 V vs. Fc/Fc + ) 37 and the potential of Fc/Fc + (3.25 vs. Li/Li + ) 40 ), making PT an attractive candidate for positive electrode materials.…”