Theoretical insight on PTB7:PC71BM, PTB7-th:PC71BM and Si-PCPDTBT:PC71BM interactions governing blend nanoscale morphology for efficient solar cells

The nanoscale morphology of solution processed bulk heterojunctions is governed by miscibility of donor and acceptor in the selected solvent and drying of the layer during processing. Ternary blends are of great interest for high efficiency polymer solar cells, but prediction of their morphology is highly complex. Here we perform atomistic simulations to study the miscibility of three different polymers of interest for ternary organic photovoltaics (the small band gap polymers PTB7 and PTB7-th, and the sensitizer Si-PCPDTBT) with the fullerene acceptor PC71BM. The free energy of mixing of fullerenes with polymers is calculated as a function of the relative concentration. The blend density is also varied to simulate out-of-equilibrium conditions occurring during layer processing. By analyzing the results within the Flory–Huggins theory we find that, for a specific range of fullerene weight ratios and densely packed blends the sensitizer is most likely located in the host polymer phase due to its low miscibility with the fullerene. This configuration is the preferred one for the solar cell in order to deactivate hole traps typically formed in the binary blends and reduce recombination. Notably, we find that these results can be different qualitatively at lower density and in out-of-equilibrium blends. This work shows that weight ratios and density can be in principle chosen to select specific morphologies in ternary organic blends

UV-enhanced Ozone Sensing Response of Al-doped Zinc Oxide Nanocrystals at Room Temperature

International audienceIn this work, we focus on ozone (O3) detection at room temperature in the main objective to be well suited for most of flexible substrates. Aluminum doped zinc oxide (AZO) nanoparticles were deposited in thin films to be used as ozone gas sensors. It was demonstrated that the nanoparticles had good sensitivity to O3 at low temperature ( 125°C) when the sensor was exposed to UV illumination. This study provides an easy and efficient way to obtain O3 gas sensors at temperature from 25°C up to 125°C by a simple and versatile solution-process. Electrical resistance measurements at 25°C under UV irradiation showed that AZO thin films were sensitive even at a low ozone concentration (35 ppb)

UV-enhanced Ozone Sensing Response of Al-doped Zinc Oxide Nanocrystals at Room Temperature

International audienceIn this work, we focus on ozone (O3) detection at room temperature in the main objective to be well suited for most of flexible substrates. Aluminum doped zinc oxide (AZO) nanoparticles were deposited in thin films to be used as ozone gas sensors. It was demonstrated that the nanoparticles had good sensitivity to O3 at low temperature ( 125°C) when the sensor was exposed to UV illumination. This study provides an easy and efficient way to obtain O3 gas sensors at temperature from 25°C up to 125°C by a simple and versatile solution-process. Electrical resistance measurements at 25°C under UV irradiation showed that AZO thin films were sensitive even at a low ozone concentration (35 ppb)

Liquid Crystal α,ω-Hexyl-Distyryl-Bithiophene: Morphology and Charge Tranport Properties in Organic Thin Film Transistors

International audienc

A New Active Organic Component for Flexible Ammonia Gas Sensors

The objective of this study was to realize flexible gas sensors using low cost solution processing such as drop casting. As active sensor material, a p-type organic semiconductor, αα-ωω-hexyl-distyrylbithiophene (DH-DS2T), was used. DH-DS2T based transistors exhibit high mobility together with a good air stability. As a chemical compound, DH- DS2T presents a good solubility in common organic solvent, which means thin films could also processed by solution fabrication. Sensor responses were studied by measuring the current through the semiconductor organic film as an ammonia gas concentration function (NH3: 25, 50, and 100 ppm). We demonstrate here that DH-DS2T has efficient sensor responses and leads to an efficient fully solution processed gas sensor on flexible substrate