Next-generation biomedical devices will need to be self-powered and conformable to human skin or other tissue. Such devices would enable the accurate and continuous detection of physiological signals without the need for an external power supply or bulky connecting wires. Self-powering functionality could be provided by flexible photovoltaics that can adhere to moveable and complex three-dimensional biological tissues and skin. Ultra-flexible organic power sources that can be wrapped around an object have proven mechanical and thermal stability in long-term operation, making them potentially useful in human-compatible electronics. However, the integration of these power sources with functional electric devices including sensors has not yet been demonstrated because of their unstable output power under mechanical deformation and angular change. Also, it will be necessary to minimize high-temperature and energy-intensive processes when fabricating an integrated power source and sensor, because such processes can damage the active material of the functional device and deform the few-micrometre-thick polymeric substrates. Here we realize self-powered ultra-flexible electronic devices that can measure biometric signals with very high signal-to-noise ratios when applied to skin or other tissue. We integrated organic electrochemical transistors used as sensors with organic photovoltaic power sources on a one-micrometre-thick ultra-flexible substrate. A high-throughput room-temperature moulding process was used to form nano-grating morphologies (with a periodicity of 760 nanometres) on the charge transporting layers. This substantially increased the efficiency of the organophotovoltaics, giving a high power-conversion efficiency that reached 10.5 per cent and resulted in a high power-per-weight value of 11.46 watts per gram. The organic electrochemical transistors exhibited a transconductance of 0.8 millisiemens and fast responsivity above one kilohertz under physiological conditions, which resulted in a maximum signal-to-noise ratio of 40.02 decibels for cardiac signal detection. Our findings offer a general platform for next-generation self-powered electronics.

Extensive efforts have been devoted during the last decade to organic solar cell research that has led to remarkable progress and achieved power conversion efficiencies (PCEs) in excess of 10%. Among the existing flexible organic solar cells, ultrathin organic solar cells with a total thickness <10 µm have important advantages, including good mechanical bending stabilities and good conformability. These advantages have led to power generation solutions for wearable electronics. In this essay, the progress of flexible and ultrathin organic solar cells, and the future research directions pertaining to these cells are discussed based on the potential applications of textile‐compatible solar cells. Both process engineering and development of the material of ultrathin substrate films have improved the PCE of ultrathin organic solar cells, which in turn have led to the small PCE difference between flexible organic solar cells with substrate thickness >10 µm and ultrathin organic solar cells with substrate thickness ≤10 µm. Key technologies for the further improvement of PCE of flexible/ultrathin organic solar cells are discussed. Strategies to improve the stability and some important aspects, which determine the mechanical robustness of flexible organic solar cells, are also presented and discussed.

A new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials is demonstrated. The nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields a simplified tandem structure fabricated with only four component layers and a high tandem efficiency of 10.8%.

Simultaneously achieving high optical transparency and excellent charge mobility in semiconducting polymers has presented a challenge for the application of these materials in future "flexible" and "transparent" electronics (FTEs). Here, by blending only a small amount (∼15 wt %) of a diketopyrrolopyrrole-based semiconducting polymer (DPP2T) into an inert polystyrene (PS) matrix, we introduce a polymer blend system that demonstrates both high field-effect transistor (FET) mobility and excellent optical transparency that approaches 100%. We discover that in a PS matrix, DPP2T forms a web-like, continuously connected nanonetwork that spreads throughout the thin film and provides highly efficient 2D charge pathways through extended intrachain conjugation. The remarkable physical properties achieved using our approach enable us to develop prototype high-performance FTE devices, including colorless all-polymer FET arrays and fully transparent FET-integrated polymer light-emitting diodes.semiconducting polymer | organic electronics | flexible and transparent device | polymer blend | charge transport O ptically transparent and mechanically flexible circuitries have long been desired for next-generation electronics requiring unprecedented features, such as "see-through" visibility, deformability, and even skin-attachable functionality for health care systems (1-3). This new paradigm for electronic applications has motivated researchers to eagerly pursue new innovative semiconducting materials, and one promising candidate is the class of materials called semiconducting conjugated polymers (4). Their unique benefits, including mechanical flexibility, light weight, and processing advantages based on high-throughput fabrication processes using solution-printing technologies, have accelerated the development of these materials as key building blocks for next-generation ubiquitous systems (2, 5, 6). Nevertheless, these materials still cannot fulfill the ultimate requirements for future "flexible" and "transparent" electronics (FTEs). Together with their inferior charge-carrier mobility because of conformational and energetic disorder (7), their high light absorption in the visible range, which is inherent to this class of materials (absorption coefficient ∼10 5 cm −1 ) (8), makes it difficult to apply these materials in FTEs. Indeed, despite extensive investigations seeking a suitable model system for FTEs by varying the polymer-structure design and the processing techniques used, the simultaneous achievement of optical transparency and high mobility in semiconducting polymers remains a formidable challenge (9, 10).Among the various types of semiconducting polymers, lowbandgap polymers using the donor-acceptor (D-A) copolymerization scheme are promising candidate materials for FTE applications. These semiconducting copolymers usually exhibit much less absorption in the visible range compared with other typical midbandgap polymers because of their red-shifted π-π* absorption spectrum, which exhibits strong absorption in the ne...

Nucleation and growth processes can be effectively controlled in organic semiconductor films through a new concept of template-mediated molecular crystal seeds during the phase transition; the effective control of these processes ensures millimeter-scale crystal domains, as well as the performance of the resulting organic films with intrinsic hole mobility of 18 cm(2) V(-1) s(-1).

Flexible and biocompatible integrated photo‐charging devices consisting of photovoltaic cells and energy storage units can provide an independent power supply for next‐generation wearable electronics or biomedical devices. However, current flexible integrated devices exhibit low total energy conversion and storage efficiency and large device thickness, hindering their applicability towards efficient and stable self‐powered systems. Here, a highly efficient and ultra‐thin photo‐charging device with a total efficiency approaching 6% and a thickness below 50 µm is reported, prepared by integrating 3‐µm‐thick organic photovoltaics on 40 µm‐thick carbon nanotube/polymer‐based supercapacitors. This flexible photo‐charging capacitor delivers much higher performance compared with previous reports by tuning the electrochemical properties of the composite electrodes, which reduce the device thickness to 1/8 while improving the total efficiency by 15%. The devices also exhibit a superior operational stability (over 96% efficiency retention after 100 charge/discharge cycles for one week) and mechanical robustness (94.66% efficiency retention after 5000 times bending at a radius of around 2 mm), providing a high‐power and long‐term operational energy source for flexible and wearable electronics.

Highly efficient P-I-N type perovskite/bulk-heterojunction (BHJ) integrated solar cells (ISCs) with enhanced fill factor (FF) (≈80%) and high near-infrared harvesting (>30%) are demonstrated by optimizing the BHJ morphology with a novel n-type polymer, N2200, and a new solvent-processing additive. This work proves the feasibility of highly efficient ISCs with panchromatic absorption as a new photovoltaic architecture and provides important design rules for optimizing ISCs.

Flexible organic photovoltaics (OPVs) are promising power sources for wearable electronics. However, it is challenging to simultaneously achieve high efficiency as well as good stability under various stresses. Herein, we demonstrate the fabrication of highly efficient (efficiency, 13.2%) and stable OPVs based on nonfullerene blends by a single-step postannealing treatment. The device performance decreases dramatically after annealing at 90 °C and is fully recovered after annealing at 150 °C. Glass-encapsulated annealed OPVs show good environmental stability with 4.8% loss in efficiency after 4,736 h and an estimatedT80lifetime (80% of the initial power conversion efficiency) of over 20,750 h in the dark under ambient condition andT80lifetime of 1,050 h at 85 °C and 30% relative humidity. This environmental stability is enabled by the synergetic effect of the stable morphology of donor/acceptor blends and thermally stabilized interfaces due to doping. Furthermore, the high efficiency and good stability are almost 100% retained in ultraflexible OPVs and minimodules which are mechanically robust and have long-term operation capability and thus are promising for future self-powered and wearable electronics.