Lalat Indu Giri

Exciton quenching by diffusion of 2,3,5,6-tetrafluoro-7,7',8,8'-tetra cyano quino dimethane and its consequences on joule heating and lifetime of organic light-emitting diodes.

In this Letter, the effect of F(4)-TCNQ insertion at the anode/hole transport layer (HTL) interface was studied on joule heating and the lifetime of organic light-emitting diodes (OLEDs). Joule heating was found to reduce significantly (pixel temperature decrease by about 10 K at a current density of 40 mA/cm(2)) by this insertion. However, the lifetime was found to reduce significantly with a 1 nm thick F(4)-TCNQ layer, and it improved by increasing the thickness of this layer. Thermal diffusion of F(4)-TCNQ into HTL leads to F(4)-TCNQ ionization by charge transfer, and drift of these molecules into the emissive layer caused faster degradation of the OLEDs. This drift was found to reduce with an increase in the thickness of F(4)-TCNQ.

Elucidation on Joule heating and its consequences on the performance of organic light emitting diodes

Current work presents a quantitative analysis of Joule heating by temperature measurements using infrared thermography and heat estimation of organic light emitting diodes (OLEDs) and their correlation with device life time. These temperature measurements were performed at 10, 20, 30, 40, and 50 mA/cm2 current densities and studied with operational time. The temperature rise of the device has increased from 9.8 to 16.6 °C within 168 h at an operating current density of 40 mA/cm2. This has been ascribed as due to the external contamination by water, oxygen, and dust particles as well as by internal heat generation. Encapsulation of the device avoids external degradation of OLEDs by preventing the destruction caused by these external contaminations. In this way, encapsulation has led to the decreased temperature rise of 12.4 °C within the duration of 168 h, which reflects the improved stability of the device. The temperature measured has been used to calculate the heat generated inside the device by solving...

Conductive cooling in white organic light emitting diode for enhanced efficiency and life time

We demonstrate white organic light emitting diodes with enhanced efficiency (26.8 lm/W) and life time (∼11 000 h) by improved heat dissipation through encapsulation composed of a metal (Cu, Mo, and Al) and mica sheet joined using thermally conducting epoxy. Finite element simulation is used to find effectiveness of these encapsulations for heat transfer. Device temperature is reduced by about 50% with the encapsulation. This, consequently, has improved efficiency and life time by about 30% and 60%, respectively, with respect to glass encapsulation. Conductive cooling of device is suggested as the possible cause for this enhancement.

Thermal diffusivity estimation of templated nanocomposite using frequency modulated infrared imaging

Thermal diffusivity of anodic alumina (AAO) templated bismuth telluride nanowires has been measured using recently proposed frequency modulated thermal wave imaging (FMTWI). The technique provides a fast and efficient non-contact approach for in-plane thermal characterization of nanomaterials. An intensity modulated up-chirp signal is applied as photothermal excitation and the thermal response is monitored using an infrared (IR) thermography based temperature sensing system. Thermal diffusivity of the sample is experimentally assessed using the multiple phase information extracted from a single run of the experiment. This feature considerably reduces the operational time of the experiment as compared to similar lock-in thermography based approaches. This unique approach of solely using the phase information for thermal diffusivity measurements, allows the experiment to be more immune to the local variations in surface temperature and emissivity of the radiating surface. The experimental details of the technique are discussed, with practical measurement of thermal diffusivity of Bi2Te3/AAO nanocomposite in direction perpendicular to the nanochannel axis.