Based on the WKB approximation of the tunneling model, we calculate the J–V characteristics of organic light-emitting devices (OLEDs) having buffer layers of different thickness. The results show how the insertion of a buffer layer with proper thickness lowers the OLED turn-on voltage. Further calculation suggests some parameters, such as the resistivity ratio and the position of the conduction band minimum of the buffer layer relative to the lowest unoccupied molecular orbital of the organic layer, are important in selecting a buffer material. A quantitative estimation of the optimal buffer layer thickness is also presented to serve as a guide to device design. The model is validated by comparison of its predictions to experimental results.

Small-molecule organic solar cells with a structure of indium tin oxide (ITO)\tris-8-hydroxy-quinolinato aluminum (Alq3) (2nm)\fullerene (C60) (40nm)\copper phthalocyanine (CuPc) (32nm)\Au (40nm) were fabricated. The shelf lifetime of unencapsulated devices was over 1500h, and the power conversion efficiency reached 0.76% under AM1.5G (air mass 1.5 global) 75mW∕cm2. The long lifetime was attributed to the inverted structure compared to the conventional ITO\CuPc\C60\buffer\Al structure since the former could effectively protect C60 from the diffusion of oxygen and modify interfacial electrical properties. The introduction of a 2nm Alq3 layer into the cells enhanced the power conversion efficiency by more than 20 times. The presence of the thin Alq3 film on the ITO substrate lowered the substrate work function and hence increased the electric field in the organic layers, which was beneficial to the collection of free carriers. The reasons for the degradation of such kind of organic solar cells are analyzed in detail.

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Materials that undergo a reversible change of crystal structure through martensitic transformation (MT) possess unusual functionalities including shape memory, superelasticity and low/negative thermal expansion. These properties have many advanced applications, such as actuators, sensors and energy conversion, but are limited typically in a narrow temperature range of tens of Kelvin.Here we report that, by creating a nano-scale concentration modulation via phase separation, the MT can be rendered continuous by an in-situ elastic confinement mechanism. Through a model titanium alloy, we demonstrate that the elastically confined continuous MT has unprecedented properties, © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 such as superelasticity from below 4.2 K to 500 K, fully tunable and stable thermal expansion, from positive, through zero, to negative, from below 4.2 K to 573 K, and high strength-to-modulus ratio across a wide temperature range. The elastic tuning on the MT, together with a significant extension of the crystal stability limit, provides new opportunities to explore advanced materials.