Electrocaloric cooling technologies, enabled by the discovery of the giant electrocaloric effect in dielectrics more than a decade ago, represents a zero-globalwarming-potential, environment-benign cooling alternative. Benefited from its nature as an electricity-driven capacitor, the electrocaloric working body renders the great advantages in the energy efficiency and the device integration. The decade-long efforts on advancing the technology revealed many promising material candidates with matured manufacturing protocols, as well as intriguing device prototypes for applications beyond the traditional vapor compression based cooling. This article presents the recent advances in electrocaloric cooling technologies, from material improvements to device demonstrations. The environmental impact and the energy efficiency of the technology were evaluated by the total effective warming impact and the material COP, respectively. In addition to the current progresses achieved by the decade-long research effort, the existing challenges and potential opportunities brought by the electrocaloric refrigeration will be discussed.

Fluorescent carbon dots (CDs) are compelling optical emitters to construct white light‐emitting diodes (WLEDs). However, it remains a challenge to achieve large‐scale and highly efficient single‐component white‐light‐emissive CDs suitable for WLED applications. Herein, a low cost, fast processable, environmentally friendly, and one‐step synthetic approach is developed for the preparation of gram‐scale and highly efficient single‐component white‐light‐emissive carbonized polymer dots (SW‐CPDs). It is revealed that hybrid fluorescence/phosphorescence components cooperatively contribute to the emergence of white light emission. The SW‐CPDs exhibit a record quantum yield (QY) of ≈41% for the white light emission observed in solid‐state CD systems, while the QY of the phosphorescence is ≈23% under ambient conditions. Heavy doping of N and P elements as well as presence of covalently cross‐linked polymer frameworks is suggested to account for the emergence of hybrid fluorescence/phosphorescence, which is supported by the experimental results and theoretical calculations. A WLED is fabricated by applying the SW‐CPDs on an UV‐LED chip, showing favorable white‐light‐emitting characteristics with a high luminous efficacy of 18.7 lm W−1 that is comparable to that of state‐of‐the‐art WLEDs reported before.

Rapid advances in sensing technologies are leading to the development of integrated wearable electronics for biomedical applications. Piezoelectric materials have great potential for implantable devices because of their self-powered sensing capacities. The soft and highly deformable surfaces of most tissues in the human body, however, restrict the wide use of piezoelectric materials, which feature low stretchability. Flexible piezoelectric polyvinylidene fluoride films that could conformably integrate with human bodies would have advantages in health monitoring. Here, a Kirigami technique with linear cut patterns has been employed to design a stretchable piezoelectric sensor with enhanced piezoelectricity. A parametric Finite Element Analysis study is first performed to investigate its mechanical behaviour, followed by experiments. An inter-segment electrode connection approach is proposed to further enhance the piezoelectric performance of the sensor. The voltage output shows superior performance with 2.6 times improvement compared to conventionally continuous electrodes. Dynamic tests with a range of frequencies and strains are performed to validate the sensor design. With its high performance in large strain measurements, the Kirigami-based sensing system shows promise in stretchable electronics for biomedical devices.

No abstract