Great improvements in the development of organic photovoltaic (OPV) devices have been reported over the years; however, the overall efficiency and operational lifetimes of the devices must be improved.
Hybrid
perovskites form an extremely attractive class of materials
for large scale, low-cost photovoltaic applications. Fullerene-based
charge extraction layers have emerged as a viable n-type charge collection
layer, and in “inverted” p–i–n device
architectures the solar cells are approaching efficiencies of 20%.
However, the regular n–i–p devices employing fullerenes
still lag behind in performance. Here, we show that partial solubility
of fullerene derivatives in the aprotic solvents used for the perovskites
makes it challenging to retain integral films in multilayer solution
processing. To overcome this issue we introduce cross-linkable fullerene
derivatives as charge collection layers in n–i–p planar
junction perovskite solar cells. The cross-linked fullerene layers
are insolubilized and deliver improved performance in solar cells
enabled by a controllable film thickness.
Understanding the degradation mechanisms in organic photovoltaics is crucial in order to develop stable organic semiconductors and robust device architectures. The rapid loss of efficiency, referred to as burn-in, is a major issue to be addressed. This study reports on the influence of the electron transport layer (ETLs) and UV light on the drop of open-circuit voltage (V) for P3HT:PCBM-based devices. The results show that V loss is induced by the UV and, more importantly, that the ETL can amplify it, with TiO yielding a stronger drop than ZnO. Using impedance spectroscopy (IS) and X-ray photoelectron spectroscopy (XPS), different degradation mechanisms were identified according to whether the ETL is TiO or ZnO. For TiO-based devices, the formation of an interface dipole was identified, resulting in a loss of the flat-band potential (V) and, thus, of the V. For ZnO-based devices, chemical modifications of the metal oxide and active layer at the interface were detected, resulting in a doping of the active layer which impacts the V. This study highlights the role of the architecture and, more specifically, of the ETL in the severity of burn-in and degradation pathways.
In this work, nanoimprint lithography combined with standard anodization etching is used to make perfectly organised triangular arrays of vertical cylindrical alumina nanopores onto standard <100>−oriented silicon wafers. Both the pore diameter and the period of alumina porous array are well controlled and can be tuned: the periods vary from 80 to 460 nm, and the diameters vary from 15 nm to any required diameter. These porous thin layers are then successfully used as templates for the guided epitaxial growth of organised mono-crystalline silicon nanowire arrays in a chemical vapour deposition chamber. We report the densities of silicon nanowires up to 9 × 109 cm−2 organised in highly regular arrays with excellent diameter distribution. All process steps are demonstrated on surfaces up to 2 × 2 cm2. Specific emphasis was made to select techniques compatible with microelectronic fabrication standards, adaptable to large surface samples and with a reasonable cost. Achievements made in the quality of the porous alumina array, therefore on the silicon nanowire array, widen the number of potential applications for this technology, such as optical detectors or biological sensors.
We synthesized a novel bis-azide
low-band gap cross-linkable molecule
N
3
-[CPDT(FBTTh
2
)
2
] with wide absorption.
This compound is of interest as an additive in polymer/fullerene bulk
heterojunction solar cells. In addition to providing efficient thermal
stabilization of the morphology, the additive can harvest additional
solar light compared with pristine poly(3-hexyl thiophene) to improve
the power-conversion efficiency (PCE). The additional donor material
was visualized from the appearance of additional external quantum
efficiency contributions between 650 and 800 nm. An open-circuit voltage
increase of ∼2% compensates the decrease in the short-circuit
current of ∼2% to achieve a fully thermally stabilized PCE
of 3.5% after 24 h of annealing at 150 °C.
The production and characterization of ultradense, planarized, and organized silicon nanowire arrays with good crystalline and optical properties are reported. First, alumina templates are used to grow silicon nanowires whose height, diameter, and density are easily controlled by adjusting the structural parameters of the template. Then, post-processing using standard microelectronic techniques enables the production of high-density silicon nanowire matrices featuring a remarkably flat overall surface. Different geometries are then possible for various applications. Structural analysis using synchrotron X-ray diffraction reveals the good crystallinity of the nanowires and their long-range periodicity resulting from their high-density organization. Transmission electron microscopy also shows that the nanowires can grow on nonpreferential substrate, enabling the use of this technique with universal substrates. The good geometry control of the array also results in a strong optical absorption which is interesting for their use in nanowire-based optical sensors or similar devices.
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