We have developed a charge transport model that explicitly accounts for ion migration. This model has been used to interpret measured current–voltage characteristics that show hysteresis.
Thin
film lead halide perovskite cells, where the perovskite layer is deposited
directly onto a flat titania blocking layer, have reached AM 1.5 efficiencies
of over 15%, showing that the mesoporous
scaffold used in early types of perovskite solar cells is not essential.
We used a variety of techniques to gain a better understanding of
thin film perovskite cells prepared by a solution-based method. Twelve
cells were studied, which showed AM 1.5 efficiencies of ∼11%.
The properties of the cells were investigated using impedance spectroscopy,
intensity-modulated photovoltage spectroscopy (IMVS), intensity-modulated
photocurrent spectroscopy (IMPS), and open-circuit photovoltage decay
(OCVD). Despite the fact that all 12 cells were prepared at the same
time under nominally identical conditions, their behavior fell into
two distinct groups. One half of the cells exhibited ideality factors of m ≈
2.5, and the other half showed ideality factors of m ≈ 5. Impedance spectroscopy carried out under illumination
at open circuit for a range of intensities showed that the cell capacitance
was dominated by the geometric capacitance of the perovskite layer
rather than the chemical or diffusion capacitance due to photogenerated
carriers. The voltage dependence of the recombination resistance gave
ideality factors similar to those derived from the intensity dependence
of the open-circuit voltage. The IMVS time constant was determined
by the product of the geometric capacitance and the recombination
resistance. The two types of cells gave very different OCVD responses.
The cells with m ≈ 2.5 showed a persistent
photovoltage effect that was absent in the case of the cells with
higher ideality factors. The IMPS responses provide evidence of minor
efficiency losses by recombination under short-circuit conditions.
Stainless steel based dye solar cells have been upscaled from small, laboratory size test cells of 0.32 cm2 active area to 6 cm x 6 cm "mini-modules" with active areas ca. 15 cm2. Stainless steel works as the photoelectrode substrate whilst the counter electrode is prepared on indium-doped tin oxide coated polyethyleneterephtalate or polyethylenenaphtalate plastic foil (fluorine-doped tin oxide coated glass as a reference). Additional current collector structures were deposited on the counter electrode substrate with inkjet-printing of silver nanoparticle ink in order to reduce the lateral resistance of the plastic foil. Flexible substrates enable roll-to-roll type industrial manufacturing of the cells and the steel's superior conductivity compared to the typical substrate materials such as glass and plastic makes it possible to prepare even substantially larger modules. The best efficiencies obtained this far with the "mini-module" using a stainless steel photoelectrode are 2.5% with a platinum-sputtered indium-doped tin oxide coated polyethyleneterephtalate counter electrode and 3.4% with a thermally platinized fluorine-doped tin oxide coated glass counter electrode. These efficiencies are on the same level than those measured with small cells prepared with similar methods and materials (3.4%-4.7%, depending on configuration, which are amongst the highest reported for this kind of a dye solar cell). Replacing expensive conducting glass with steel and plastic foils as the substrate materials leads also to economical savings in the cell production.
This paper provides experimental results regarding an emerging physical-layer concept within the field of military communications, viz. the full-duplex 'radio shield', by building on the recently discovered full-duplex technology that allows an individual radio device to simultaneously transmit and receive (STAR) on the same spectrum. Its basic idea is to protect the surroundings of a radio device by broadcasting powerful jamming while successfully receiving tactical transmissions on overlapping frequencies. The jamming creates a protective dome of interference around such a military full-duplex radio (MFDR). The experimental results reported herein prove that the radio shield yields a large SINR advantage against interception, even though a fully practical full-duplex radio prototype with residual self-interference is used. Moreover, we show that the prototype radio shield is capable of preventing the control of improvised explosives or rogue drones while simultaneously receiving tactical signals. Therefore, the full-duplex radio shield can give armed forces a significant technical lead over an enemy by preventing it from using the frequency band for offensive purposes.
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