1,184 research outputs found
Exceeding the Shockley-Queisser limit within the detailed balance framework
The Shockley-Queisser limit is one of the most fundamental results in the
field of photovoltaics. Based on the principle of detailed balance, it defines
an upper limit for a single junction solar cell that uses an absorber material
with a specific band gap. Although methods exist that allow a solar cell to
exceed the Shockley-Queisser limit, here we show that it is possible to exceed
the Shockley-Queisser limit without considering any of these additions. Merely
by introducing an absorptivity that does not assume that every photon with an
energy above the band gap is absorbed, efficiencies above the Shockley-Queisser
limit are obtained. This is related to the fact that assuming optimal
absorption properties also maximizes the recombination current within the
detailed balance approach. We conclude that considering a finite thickness for
the absorber layer allows the efficiency to exceed the Shockley-Queisser limit,
and that this is more likely to occur for materials with small band gaps.Comment: 6 pages, 3 figure
High-efficiency GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy
We report the initial results of GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy (MBE) technique. For GaAs single-junction solar cell, with the application of AlInP as the window layer and GaInP as the back surface field layer, the photovoltaic conversion efficiency of 26% at one sun concentration and air mass 1.5 global (AM1.5G) is realized. The efficiency of 16.4% is also reached for GaInP solar cell. Our results demonstrate that the MBE-grown phosphide-contained III-V compound semiconductor solar cell can be quite comparable to the metal-organic-chemical-vapor-deposition-grown high-efficiency solar cell
Tuning up the performance of GaAs-based solar cells by inelastic scattering on quantum dots and doping of AlyGa1-ySb type-II dots and AlxGa1-xAs spacers between dots
We used AlGaSb/AlGaAs material system for a theoretical study of photovoltaic
performance of the proposed GaAs-based solar cell in which the type-II quantum
dot (QDs) absorber is spatially separated from the depletion region. Due to
inelastic scattering of photoelectrons on QDs and proper doping of both QDs and
their spacers, concentrated sunlight is predicted to quench recombination
through QDs. Our calculation shows that 500-sun concentration can increase the
Shockley-Queisser limit from 35% to 40% for GaAs single-junction solar cells.Comment: 8 pages, 7 figures; Contributed paper to SPIE Photonics West, San
Francisco, CA, USA, February 201
Wide-band-gap InAlAs solar cell for an alternative multijunction approach
We have fabricated an In_(0.52)Al_(0.48)As solar cell lattice-matched to InP with efficiency higher than 14% and maximum external quantum efficiency equal to 81%. High quality, dislocation-free In_xAl_(1−x)As alloyed layers were used to fabricate the single junction solar cell. Photoluminescence of In_xAl_(1−x)As showed good material quality and lifetime of over 200 ps. A high band gap In_(0.35)Al_(0.65)As window was used to increase light absorption within the p-n absorber layer and improve cell efficiency, despite strain. The InAlAs top cell reported here is a key building block for an InP-based three junction high efficiency solar cell consisting of InAlAs/InGaAsP/InGaAs lattice-matched to the substrate
Theoretical Limits of Photovoltaics Efficiency and Possible Improvements by Intuitive Approaches Learned from Photosynthesis and Quantum Coherence
In this review, we present and discussed the main trends in photovoltaics
with emphasize on the conversion efficiency limits. The theoretical limits of
various photovoltaics device concepts are presented and analyzed using a
flexible detailed balance model where more discussion emphasize is toward the
losses. Also, few lessons from nature and other fields to improve the
conversion efficiency in photovoltaics are presented and discussed as well.
From photosynthesis, the perfect exciton transport in photosynthetic complexes
can be utilized for PVs. Also, we present some lessons learned from other
fields like recombination suppression by quantum coherence. For example, the
coupling in photosynthetic reaction centers is used to suppress recombination
in photocells.Comment: 47 pages, 22 figures. arXiv admin note: text overlap with
arXiv:1307.5093, arXiv:1105.4189 by other author
Ideal Bandgap in a 2D Ruddlesden-Popper Perovskite Chalcogenide for Single-junction Solar Cells
Transition metal perovskite chalcogenides (TMPCs) are explored as stable,
environmentally friendly semiconductors for solar energy conversion. They can
be viewed as the inorganic alternatives to hybrid halide perovskites, and
chalcogenide counterparts of perovskite oxides with desirable optoelectronic
properties in the visible and infrared part of the electromagnetic spectrum.
Past theoretical studies have predicted large absorption coefficient, desirable
defect characteristics, and bulk photovoltaic effect in TMPCs. Despite recent
progresses in polycrystalline synthesis and measurements of their optical
properties, it is necessary to grow these materials in high crystalline quality
to develop a fundamental understanding of their optical properties and evaluate
their suitability for photovoltaic application. Here, we report the growth of
single crystals of a two-dimensional (2D) perovskite chalcogenide, Ba3Zr2S7,
with a natural superlattice-like structure of alternating double-layer
perovskite blocks and single-layer rock salt structure. The material
demonstrated a bright photoluminescence peak at 1.28 eV with a large external
luminescence efficiency of up to 0.15%. We performed time-resolved
photoluminescence spectroscopy on these crystals and obtained an effective
recombination time of ~65 ns. These results clearly show that 2D
Ruddlesden-Popper phases of perovskite chalcogenides are promising materials to
achieve single-junction solar cells.Comment: 4 Figure
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