Flexoelectric materials and their related applications: A focused review

Flexoelectricity refers to the mechanical-electro coupling between strain gradient and electric polarization, and conversely, the electro-mechanical coupling between electric field gradient and mechanical stress. This unique effect shows a promising size effect which is usually large as the material dimension is shrunk down. Moreover, it could break the limitation of centrosymmetry, and has been found in numerous kinds of materials which cover insulators, liquid crystals, biological materials, and semiconductors. In this review, we will give a brief report about the recent discoveries in flexoelectricity, focusing on the flexoelectric materials and their applications. The theoretical developments in this field are also addressed. In the end, the perspective of flexoelectricity and some open questions which still remain unsolved are commented upon.

Pulsed laser deposition of amorphous InGaZnO_(4)as an electron transport layer for perovskite solar cells

Hybrid perovskite solar cells(PSCs)have been intensively studied in recent years because of their high efficiency and low costs.For PSCs,the electron transport layer(ETL)is a key for its photoelectric conversion efficiency.Here we demonstrate the application of amorphous InGaZnO_(4)thin films as ETL for efficient PSCs by pulsed laser deposition(PLD).The PSC device using such InGaZnO_(4)amorphous film as ETL has achieved an efficiency of 15.1%.The outstanding performance is attributed to the excellent properties of amorphous InGaZnO_(4)oxide thin films,including high electron mobility and high transparency,what is more,the electronic properties of the films can be controlled by changing the partial pressure of oxygen in the deposition chamber and post-deposition annealing process.Our result will be helpful for preparation of large area PSCs and other opto-electric devices at low temperature by physical vapor deposition method.

Compositional modulation in ZnGa_(2)0_(4) via Zn^(2+)/Ge^(4+)co-doping to simultaneously lower sintering temperature and improve microwave dielectric properties

AB_(2)O_(4)-type spinels with low relative permittivity(ε_(τ))and high quality factor(Q×f)are crucial to high-speed signal propagation systems.In this work,Zn^(2+)/Ge^(4+) co-doping to substitute Ga in ZnGa_(2)O_(4) was designed to lower the sintering temperature and adjust the thermal stability of resonance frequency simultaneously.Zn_(1+2)Ga_(2-2x)Ge_(x)O_(4)(0.1≤x≤0.5)ceramics were synthesised by the conventional solid state method.Zn^(2+)/Ge^(4+) co-substitution induced minimal variation in the macroscopical spinel structure,which effectively lowered the sintering temperature from 1385 to 1250℃.All compositions crystallized in a normal spinel structure and exhibited dense microstructures and excellent microwave dielectric properties.The compositional dependent quality factor was related to the microstructural variation,being confirmed by Raman features.A composition with x=0.3 shows the best dielectric properties with ε_(τ) ≈10.09,Q×f≈112,700 THz,and ε_(τ) ≈-75.6 ppm/℃.The negative τf value was further adjusted to be near-zero through the formation of composite ceramics with TiO_(2).