24 research outputs found
Effect of Blend Composition and Additives on the Morphology of PCPDTBT:PC71BM Thin Films for Organic Photovoltaics.
The use of solvent additives in the fabrication of bulk heterojunction polymer:fullerene solar cells allows to boost efficiencies in several low bandgap polymeric systems. It is known that solvent additives tune the nanometer scale morphology of the bulk heterojunction. The full mechanism of efficiency improvement is, however, not completely understood. In this work, we investigate the influences of blend composition and the addition of 3 vol % 1,8-octanedithiol (ODT) as solvent additive on polymer crystallization and both, vertical and lateral morphologies of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCPDTBT:PC71BM) blend thin films processed from chlorobenzene-based solutions. The nanoscale morphology is probed with grazing incidence small- and wide-angle X-ray scattering as well as X-ray reflectivity and complemented with UV/vis spectroscopy. In PCPDTBT:PC71BM films the use of ODT is found to lower the solubility of fullerene in the polymer matrix and to promote polymer crystallization, both vertical and lateral microphase separation with morphological coarsening, and formation of a fullerene-rich topping layer. The enhanced photovoltaic performance is explained by these findings
Ландшафтное проектирование (городские объекты) : учеб.-метод. пособие
Spray coating, a cost-effective and scalable technique, has been employed for fabricating titania films for solid-state dye-sensitized solar cells (ssDSSCs). The spray deposition of films is inherently based on kinetic processes with great complexity, which poses great challenges in its understanding. In the present work, the kinetics of the structure evolution of deposited films are investigated by in situ grazing-incidence small-angle x-ray scattering during spray deposition. The spray-solution is prepared via a polystyrene-block-polyethylene oxide (PS-b-PEO) template assisted sol-gel synthesis. It is turned into nanostructured titania/PS-b-PEO composite films via spray deposition. The information about nanostructure length scales of the composite film is obtained in real-time and in situ, revealing the morphological evolution during the spray deposition. The resulting mesoporous titania films serve as photoanodes of ssDSSCs, which couple with the solution-cast hole transport layer to form the active layers. The well working ssDSSCs demonstrate the successful use of spray deposition as a large-scale manufacturing process for photoanodes
Structure of Organometal Halide Perovskite Films as Determined with Grazing-Incidence X-Ray Scattering Methods
Grazing-incidence X-ray scattering (GIXS) methods have proven to be a valuable asset for investigating the morphology of thin films at different length scales. Consequently, GIXS has been applied to the fast-progressing field of organometal halide perovskites. This exciting class of materials has propelled research in the areas of cheap and sustainable photovoltaics, light emitting devices, and optoelectronics in general. Especially, perovskite solar cells (PSC) have seen a remarkable rise in power conversion efficiencies, crossing the 20% mark after only five years of research. This research news outlines GIXS studies focusing on the most challenging research topics in the perovskite field today: Current–voltage hysteresis, device reproducibility, and long-term stability of PSC are inherently linked to perovskite film morphology. On the other hand, film formation depends on the choice of precursors and processing parameters; understanding their interdependence opens possibilities to tailor film morphologies. Owing to their tunability and moisture resistance, 2D perovskites have recently attracted attention. Examples of GIXS studies with different measurement and data analysis techniques are presented, highlighting especially in-situ investigations on the many kinetic processes involved. Thus, an overview on the toolbox of GIXS techniques is linked to the specific needs of research into organometal halide perovskite optoelectronics
Light‐Induced and Oxygen‐Mediated Degradation Processes in Photoactive Layers Based on PTB7‐Th
Low-bandgap polymers are sensitive to various degradation processes, which strongly decrease their lifetime. The chemical and physical changes occurring in the low-bandgap polymer with benzodithiophene units poly[4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and its blend with the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are followed during irradiation-induced aging by combination of various characterization methods. The active layer morphology is investigated using atomic force microscopy (AFM) as well as in-operando grazing incidence small angle X-ray scattering (GISAXS), indicating morphological alterations and material loss due to chemical modifications. Optical spectroscopy gives insights into these chemical processes which lead to significant absorption losses under ambient conditions. Independent of the energy of the absorbed photons, but only in combination with oxygen, the excitation of the polymer leads to a fatal increase in oxidation probability. Fourier transform infrared (FTIR) data highlight the sensitivity of the conjugated polymer backbone to oxidation, a result of lost conjugation and therefore absorption capability. With combined AFM height and infrared (IR) mapping, the chemical degradation and material loss is confirmed on a nanoscale. Although the chemical structure is seriously damaged, the blend morphology is not undergoing major changes
In Situ Monitoring the Uptake of Moisture into Hybrid Perovskite Thin Films
Solution-processed
hybrid perovskites are of great interest for
use in photovoltaics. However, polycrystalline perovskite thin films
show strong degradation in humid atmospheres, which poses an important
challenge for large-scale market introduction. With in situ grazing
incidence neutron scattering (GISANS) we analyzed water content, degradation
products, and morphological changes during prolonged exposure to several
humidity levels. In high humidity, the formation of metastable hydrate
phases is accompanied by domain swelling, which transforms the faceted
crystals to a round-washed, pebble-like form. The films incorporate
much more water than is integrated into the hydrates, with smaller
crystals being more affected, making the degradation strongly dependent
on film morphology. Even at low humidity, water is adsorbed on the
crystal surfaces without the formation of crystalline degradation
products. Thus, although production in an ambient atmosphere is of
interest for industrial production it might lead to long-term degradation
without appropriate countermeasures like postproduction drying below
30% RH
In Situ Monitoring the Uptake of Moisture into Hybrid Perovskite Thin Films
Solution-processed
hybrid perovskites are of great interest for
use in photovoltaics. However, polycrystalline perovskite thin films
show strong degradation in humid atmospheres, which poses an important
challenge for large-scale market introduction. With in situ grazing
incidence neutron scattering (GISANS) we analyzed water content, degradation
products, and morphological changes during prolonged exposure to several
humidity levels. In high humidity, the formation of metastable hydrate
phases is accompanied by domain swelling, which transforms the faceted
crystals to a round-washed, pebble-like form. The films incorporate
much more water than is integrated into the hydrates, with smaller
crystals being more affected, making the degradation strongly dependent
on film morphology. Even at low humidity, water is adsorbed on the
crystal surfaces without the formation of crystalline degradation
products. Thus, although production in an ambient atmosphere is of
interest for industrial production it might lead to long-term degradation
without appropriate countermeasures like postproduction drying below
30% RH
Effect of Blend Composition and Additives on the Morphology of PCPDTBT:PC<sub>71</sub>BM Thin Films for Organic Photovoltaics
The use of solvent additives in the
fabrication of bulk heterojunction polymer:fullerene solar cells allows
to boost efficiencies in several low bandgap polymeric systems. It
is known that solvent additives tune the nanometer scale morphology
of the bulk heterojunction. The full mechanism of efficiency improvement
is, however, not completely understood. In this work, we investigate
the influences of blend composition and the addition of 3 vol % 1,8-octanedithiol
(ODT) as solvent additive on polymer crystallization and both, vertical
and lateral morphologies of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta
[2,1-b;3,4-b′]dithiophene)-<i>alt</i>-4,7(2,1,3-benzothiadiazole)]
and [6,6]-phenyl C<sub>71</sub>-butyric acid methyl ester (PCPDTBT:PC<sub>71</sub>BM) blend thin films processed from chlorobenzene-based solutions.
The nanoscale morphology is probed with grazing incidence small- and
wide-angle X-ray scattering as well as X-ray reflectivity and complemented
with UV/vis spectroscopy. In PCPDTBT:PC<sub>71</sub>BM films the use
of ODT is found to lower the solubility of fullerene in the polymer
matrix and to promote polymer crystallization, both vertical and lateral
microphase separation with morphological coarsening, and formation
of a fullerene-rich topping layer. The enhanced photovoltaic performance
is explained by these findings