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- Aqueous media (1)
- Dispersion of nanomaterials (1)
- Inverted solar cells (1)
- Low band-gap (1)
- Optical modeling (1)
- Organic solar cells (1)
- PCPDTBT (1)
- Protocol development (1)
We compare standard and inverted bulk heterojunction solar cells composed of PCPDTBT:PC70BM
blends. Inverted devices comprising 100 nm thick active layers exhibited short circuit currents of
15 mA/cm², 10% larger than in corresponding standard devices. Modeling of the optical field distribution
in the different device stacks proved that this enhancement originates from an increased absorption of
incident light in the active layer. Internal quantum efficiencies (IQEs) were obtained from the direct
comparison of experimentally derived and modeled currents for different layer thicknesses, yielding IQEs
of ~70% for a layer thickness of 100 nm. Simulations predict a significant increase of the light harvesting
efficiency upon increasing the layer thickness to 270 nm. However, a continuous deterioration of the
photovoltaic properties with layer thickness was measured for both device architectures, attributed to
incomplete charge extraction. On the other hand, our optical modeling suggests that inverted devices
based on PCPDTBT should be able to deliver high power conversion efficiencies (PCEs) of more than
7% provided that recombination losses can be reduced.
The sonication process is commonly used for de-agglomerating and dispersing nanomaterials in aqueous based media, necessary to improve homogeneity and stability of the suspension. In this study, a systematic step-wise approach is carried out to identify optimal sonication conditions in order to achieve a stable dispersion. This approach has been adopted and shown to be suitable for several nanomaterials (cerium oxide, zinc oxide, and carbon nanotubes) dispersed in deionized (DI) water. However, with any change in either the nanomaterial type or dispersing medium, there needs to be optimization of the basic protocol by adjusting various factors such as sonication time, power, and sonicator type as well as temperature rise during the process. The approach records the dispersion process in detail. This is necessary to identify the time Points as well as other above-mentioned conditions during the sonication process in which there may be undesirable changes, such as damage to the particle surface thus affecting surface properties. Our goal is to offer a harmonized approach that can control the Quality of the final, produced dispersion. Such a guideline is instrumental in ensuring dispersion quality repeatability in the nanoscience community, particularly in the field of nanotoxicology.