Effect of annealing on photovoltaic properties and microstructure of conventional and inverted organic solar cells using active bilayer based on liquid-crystal semiconducting polymer and fullerene

Abstract

SUMMARY Conventional and inverted organic solar cells of poly[9,9‐dioctyl‐fluorene‐co‐bithiophene] (F8T2) as liquid‐crystal semiconducting polymer and fullerene as electron acceptor were fabricated and characterized. An effect of thermal treatment of the films on annealing condition near glass transition was investigated for tuning optimization and improving the photovoltaic and optical properties. Annealing treatment below the glass transition improved the photovoltaic performance and carrier diffusion in crystal growth of active layer. The X‐ray diffraction patterns indicate a crystalline structure with molecular order of F8T2 in crystal index, 100 as a layer distance between sheets of F8T2 chains. The photovoltaic properties were based on molecular interactions with molecular ordering in active layer at crystal state. As the photovoltaic mechanisms, the F8T2 thin film as p‐type semiconducting polymer worked for electron‐donor layer to support light‐induced generation, carrier diffusion and charge transfer near interface in active layer. Copyright © 2014 John Wiley & Sons, Ltd.

Flexible Narrowband Ultraviolet Photodetectors with Photomultiplication Based on Wide Band Gap Conjugated Polymer and Inorganic Nanoparticles

“…This can be explained by the increased molecular disorder of F8T2 upon blending with ZnO NPs. Both pure F8T2 and blend F8T2/ZnO films were annealed at 80 °C for 10 min, which is below the glass transition temperature of F8T2. , The strong absorption peak at 485 nm would be originated in polarizing crystal growth of F8T2 in the film. The addition of ∼10 nm ZnO NPs disrupts the F8T2 crystalline structure, resulting in the observed decrease and blue shift of the 485 nm peak due to isotropic behavior in the amorphous phase .…”

“…Both pure F8T2 and blend F8T2/ZnO films were annealed at 80 °C for 10 min, which is below the glass transition temperature of F8T2. , The strong absorption peak at 485 nm would be originated in polarizing crystal growth of F8T2 in the film. The addition of ∼10 nm ZnO NPs disrupts the F8T2 crystalline structure, resulting in the observed decrease and blue shift of the 485 nm peak due to isotropic behavior in the amorphous phase . A slight quenching in photoluminescence and a lower 550 nm peak are observed for the blend film compared to pure F8T2 (Figure S1), indicating that charge separation occurs at F8T2/ZnO junctions. , The topographic atomic force microscopy (AFM) image of the blend film (Figure d) shows a smooth surface with a root mean square roughness of 2.5 nm.…”

J-Aggregate Behavior of Poly[(9,9- dioctyluorenyl-2,7-diyl)-alt-co-(bithiophene)] (F8T2) in Crystal and Liquid Crystal Phases

“…23,26 Manipulation of molecular order and crystallinity could cause F8T2 transformation in aggregate microstructure and morphology and greatly influence the device performances. 27,28 Alignment of F8T2 chains could be achieved via directional induction. 26,29,30 Solution processing could result in the self-assembly of the F8T2 chains into highly ordered nanostructures.…”

Organic Ultraviolet Photodetectors Exhibiting Photomultiplication, Low Dark Current, and High Stability

“…F8T2 has also been blended with PC 61 BM and used in photodetectors with the structure ITO/F8T2:PCBM/Au that showed rectifying characteristics and photocurrent densities around 2 mA cm −2 under 460 nm illumination and a −1 V bias . As a liquid crystalline polymer, F8T2 has several different phase regions and transitions, leading to variations in microstructure and morphology that can affect device performance through charge dynamics and energy levels . In fact, the band gap of F8T2, which is well‐suited for UV absorption, can vary between 2 and 3 eV depending on its phase, which is controlled by film annealing temperature and can vary between amorphous, mesophase, and ordered liquid‐crystal …”