Recent interest in flexible electronics has led to a paradigm shift in consumer electronics, and the emergent development of stretchable and wearable electronics is opening a new spectrum of ubiquitous applications for electronics. Organic electronic materials, such as π-conjugated small molecules and polymers, are highly suitable for use in low-cost wearable electronic devices, and their charge-carrier mobilities have now exceeded that of amorphous silicon. However, their commercialization is minimal, mainly because of weaknesses in terms of operational stability, long-term stability under ambient conditions, and chemical stability related to fabrication processes. Recently, however, many attempts have been made to overcome such instabilities of organic electronic materials. Here, an overview is provided of the strategies developed for environmentally robust organic electronics to overcome the detrimental effects of various critical factors such as oxygen, water, chemicals, heat, and light. Additionally, molecular design approaches to π-conjugated small molecules and polymers that are highly stable under ambient and harsh conditions are explored; such materials will circumvent the need for encapsulation and provide a greater degree of freedom using simple solution-based device-fabrication techniques. Applications that are made possible through these strategies are highlighted.

1wileyonlinelibrary.com more than 1 cm 2 V −1 s −1 . [ 1,2 ] Furthermore, several recent papers have reported that mobility values surpassing 3 cm 2 V −1 s −1 can be obtained in state-of-the-art donoracceptor (D-A) polymers based on diketopyrrolopyrrole (DPP). The DPP motif not only contributes to tight π−π spacing but also enhances the charge delocalization through its high level of co-planarity and quinoidal structure, being highly benefi cial to charge-carrier transport through intermolecular hopping. [ 2a , 3 ] Even though their stability in ambient electrochemical oxidative processes is necessary for the broadbased, high-value applications mentioned above, solution-processable polymeric semiconductors performing beyond the current levels-reliably exceeding 10 cm 2 V −1 swith an on/off ratio ( I on / I off ) of at least 10 6 -are the most compelling requirement for the progress of organic electronics.Recently, we and other groups suggested the effectiveness of controlling the branching point of the side chain from the polymer backbone for tuning intermolecular self-assembly and charge-carrier mobility. [ 3a-c,4 ] Therefore, side-chain engineering can be as important as manipulating the conjugated building blocks in the backbones when designing high-performance conjugated polymers. [ 5 ] In this work, we report the substantially enhanced charge-transport characteristics of a series of DPP-based polymers showing vastly superior FET performance (hole mobilities ( µ h ) of 12.25 cm 2 V −1 s −1 and I on / I off ≥ 10 6 together with electron mobilities ( µ e ) larger than 2 cm 2 V −1 s −1 ). These have been achieved by simply modulating the side-chain branching position (i.e., replacing the commonly used 2-octyldodecyl solubilizing group as the β -branched chain of the DPPbased polymers with the 5-octylpentadecyl chain ( ε -branched chain)). We also demonstrate the structure−property relationships regarding the interplay of the molecular packing and macroscopic charge-transport effi cacy. Results and Discussion Synthesis and CharacterizationBriefl y, 5-octyl-1-pentadecyliodide as the key ε -branched side chain ( ε -C 8 C 15 ) was obtained from commercially available ) with an on/off ratio ( I on / I off ) of at least 10 6 are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.

Conspectus Bioelectronics for healthcare that monitor the health information on users in real time have stepped into the limelight as crucial electronic devices for the future due to the increased demand for “point-of-care” testing, which is defined as medical diagnostic testing at the time and place of patient care. In contrast to traditional diagnostic testing, which is generally conducted at medical institutions with diagnostic instruments and requires a long time for specimen analysis, point-of-care testing can be accomplished personally at the bedside, and health information on users can be monitored in real time. Advances in materials science and device technology have enabled next-generation electronics, including flexible, stretchable, and biocompatible electronic devices, bringing the commercialization of personalized healthcare devices increasingly within reach, e.g., wearable bioelectronics attached to the body that monitor the health information on users in real time. Additionally, the monitoring of harmful factors in the environment surrounding the user, such as air pollutants, chemicals, and ultraviolet light, is also important for health maintenance because such factors can have short- and long-term detrimental effects on the human body. The precise detection of chemical species from both the human body and the surrounding environment is crucial for personal health care because of the abundant information that such factors can provide when determining a person’s health condition. In this respect, sensor applications based on an organic-transistor platform have various advantages, including signal amplification, molecular design capability, low cost, and mechanical robustness (e.g., flexibility and stretchability). This Account covers recent progress in organic transistor-based chemical sensors that detect various chemical species in the human body or the surrounding environment, which will be the core elements of wearable electronic devices. There has been considerable effort to develop high-performance chemical sensors based on organic-transistor platforms through material design and device engineering. Various experimental approaches have been adopted to develop chemical sensors with high sensitivity, selectivity, and stability, including the synthesis of new materials, structural engineering, surface functionalization, and device engineering. In this Account, we first provide a brief introduction to the operating principles of transistor-based chemical sensors. Then we summarize the progress in the fabrication of transistor-based chemical sensors that detect chemical species from the human body (e.g., molecules in sweat, saliva, urine, tears, etc.). We then highlight examples of chemical sensors for detecting harmful chemicals in the environment surrounding the user (e.g., nitrogen oxides, sulfur dioxide, volatile organic compounds, liquid-phase organic solvents, and heavy metal ions). Finally, we conclude this Account with a perspective on the wearable bioelectronics, especially focusing on org...

Two acceptor-acceptor (A-A) type copolymers (PIIG-BT and PIIG-TPD) with backbones composed exclusively of electron-deficient units are designed and synthesized. Both copolymers show unipolar n-type operations. In particular, PIIG-BT shows electron mobility of up to 0.22 cm(2) V(-1) s(-1). This is a record value for n-type copolymers based on lactam cores.