11,618 research outputs found
Perovskite-perovskite tandem photovoltaics with optimized bandgaps
We demonstrate four and two-terminal perovskite-perovskite tandem solar cells
with ideally matched bandgaps. We develop an infrared absorbing 1.2eV bandgap
perovskite, , that can deliver 14.8 %
efficiency. By combining this material with a wider bandgap
material, we reach monolithic two
terminal tandem efficiencies of 17.0 % with over 1.65 volts open-circuit
voltage. We also make mechanically stacked four terminal tandem cells and
obtain 20.3 % efficiency. Crucially, we find that our infrared absorbing
perovskite cells exhibit excellent thermal and atmospheric stability,
unprecedented for Sn based perovskites. This device architecture and materials
set will enable 'all perovskite' thin film solar cells to reach the highest
efficiencies in the long term at the lowest costs
Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells
Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are
prepared by electrospinning, and their properties assessed by scanning
electron, atomic and lateral force, tunnelling, and confocal microscopy, as
well as by attenuated total reflection Fourier transform-infrared spectroscopy,
photoluminescence quantum yield and spatially-resolved fluorescence.
Highlighted features include ribbon-shape of the realized fibers, and the
persistence of a network serving as a template for heterogeneous active layers
in solar cell devices. A set of favorable characteristics is evidenced in this
way in terms of homogeneous charge transport behavior and formation of
effective interfaces for diffusion and dissociation of photogenerated excitons.
The interaction of the organic filaments with light, exhibiting specific
light-scattering properties of the nanofibrous mat, might also contribute to
spreading incident radiation across the active layers, thus potentially
enhancing photovoltaic performance. This method might be applied to other
electron donor-electron acceptor material systems for the fabrication of solar
cell devices enhanced by nanofibrillar morphologies embedding conjugated
polymers and fullerene compounds.Comment: 35 pages, 9 figure
Perovskite-polymer composite cross-linker approach for highly-stable and efficient perovskite solar cells.
Manipulation of grain boundaries in polycrystalline perovskite is an essential consideration for both the optoelectronic properties and environmental stability of solar cells as the solution-processing of perovskite films inevitably introduces many defects at grain boundaries. Though small molecule-based additives have proven to be effective defect passivating agents, their high volatility and diffusivity cannot render perovskite films robust enough against harsh environments. Here we suggest design rules for effective molecules by considering their molecular structure. From these, we introduce a strategy to form macromolecular intermediate phases using long chain polymers, which leads to the formation of a polymer-perovskite composite cross-linker. The cross-linker functions to bridge the perovskite grains, minimizing grain-to-grain electrical decoupling and yielding excellent environmental stability against moisture, light, and heat, which has not been attainable with small molecule defect passivating agents. Consequently, all photovoltaic parameters are significantly enhanced in the solar cells and the devices also show excellent stability
What is moving in hybrid halide perovskite solar cells?
Organic-inorganic semiconductors, which adopt the perovskite crystal
structure, have perturbed the landscape of contemporary photovoltaics research.
In this Account, we discuss the internal motion of methylammonium lead iodide
(CHNHPbI) and formamidinium lead iodide ([CH(NH)]PbI),
covering: (i) molecular rotation-libration in the cuboctahedral cavity; (ii)
drift and diffusion of large electron and hole polarons; (iii) transport of
charged ionic defects. These processes give rise to a range of properties that
are unconventional for photovoltaic materials, including frequency-dependent
permittivity, low electron-hole recombination rates, and current-voltage
hysteresis. Multi-scale simulations - drawing from electronic structure, ab
initio molecular dynamic and Monte Carlo techniques - have been combined with
neutron scattering and ultra-fast vibrational spectroscopy to qualify the
nature and timescales of the motions. Recent experimental evidence and
theoretical models for simultaneous electron transport and ion transport in
these materials has been presented, suggesting they are mixed-mode conductors
with similarities to metal oxide perovskites developed for battery and fuel
cell applications. We expound on the implications of these effects for the
photovoltaic action. The temporal behaviour found in hybrid perovskites
introduces a sensitivity in materials characterisation to the time and length
scale of the measurement, as well as the history of each sample. It also poses
significant challenges for accurate materials and device simulations. Herein,
we critically discuss the atomistic origin of the dynamic processes.Comment: 29 pages, 3 figure
Correlated electron-hole plasma in organometal perovskites
Organic-inorganic perovskites are a class of solution-processed semiconductors holding promise for the realization of low-cost efficient solar cells and on-chip lasers. Despite the recent attention they have attracted, fundamental aspects of the photophysics underlying device operation still remain elusive. Here we use photoluminescence and transmission spectroscopy to show that photoexcitations give rise to a conducting plasma of unbound but Coulomb-correlated electron-hole pairs at all excitations of interest for light-energy conversion and stimulated optical amplification. The conductive nature of the photoexcited plasma has crucial consequences for perovskite-based devices: in solar cells, it ensures efficient charge separation and ambipolar transport while, concerning lasing, it provides a low threshold for light amplification and justifies a favourable outlook for the demonstration of an electrically driven laser. We find a significant trap density, whose cross-section for carrier capture is however low, yielding a minor impact on device performance
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