2 research outputs found
Transfer Printed P3HT/PCBM Photoactive Layers: From Material Intermixing to Device Characteristics
The fabrication of organic electronic
devices involving complex stacks of solution-processable functional
materials has proven challenging. Significant material intermixing
often occurs as a result of cross-solubility and postdeposition treatments,
rendering the realization of even the simplest bilayer architectures
rather cumbersome. In this study we investigate the feasibility of
a dry transfer printing process for producing abrupt bilayer organic
photodiodes (OPDs) and the effect of thermal annealing on the integrity
of the bilayer. The process involves the transfer of readily deposited
thin films of polyÂ(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl
C61 butyric acid methyl ester (PCBM) using a polydimethylsiloxane
(PDMS) stamp. Fabricated structures are characterized by means of
cross-sectional scanning electron microscopy (SEM), UV/vis absorption
spectroscopy, and time-of-flight secondary ion mass spectrometry (TOF-SIMS).
Joint consideration of all results unveils abrupt interfaces with
no thermal treatment applied and significant material intermixing
for samples annealed above 100 °C. The role of the thermally
assisted intermixing in determining the performance of complete devices
is evaluated through the comparison of <i>J</i>–<i>V</i> characteristics and external quantum efficiencies (EQEs)
of identical photodiodes subject to different annealing conditions.
It is shown that the performance of such devices approaches the one
of bulk heterojunction photodiodes upon thermal annealing at 140 °C
for 5 min. Our results demonstrate that transfer printing is a reliable
and simple process for the realization of functional multilayers,
paving the way for organic electronic devices incorporating complex
stacks. It further contributes to a fundamental understanding of material
composition within photoactive layers by elucidating the process of
thermally assisted intermixing
Fully-Sprayed and Flexible Organic Photodiodes with Transparent Carbon Nanotube Electrodes
In
this study, we demonstrate the feasibility of TCO-free, fully
sprayed organic photodiodes on flexible polyethylene terephthalate
(PET) substrates. Transparent conducting films of single-wall carbon
nanotubes are spray deposited from aqueous solutions. Low roughness
is achieved, and films with sheet resistance values of 160 Ω/sq
at 84% in transmittance are fabricated. Process issues related to
the wetting of CNTs are then examined and solved, enabling successive
spray depositions of a polyÂ(3,4-ethylenedioxythiophene):polyÂ(styrenesulfonate)
(PEDOT:PSS) layer and a blend of regioregular polyÂ(3-hexylthiophene-2,5-diyl)
and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The active
layer is then optimized, achieving a process yield above 90% and dark
currents as low as 10<sup>–4</sup> mA/cm<sup>2</sup>. An external
quantum efficiency of 65% and high reproducibility in the performance
of the devices are obtained. Finally, the impact of the characteristics
of the transparent electrode (transmittance and sheet resistance)
on the performances of the device are investigated and validated through
a theoretical model and experimental data