The authors report an enhanced infrared spectral response of GaAs-based solar cells that incorporate type II GaSb quantum dots ͑QDs͒ formed using interfacial misfit array growth mode. The material and devices, grown by molecular beam epitaxy, are characterized by current-voltage and spectral response characteristics. From 0.9 to 1.36 m, these solar cells show significantly more infrared response compared to reference GaAs cells and previously reported InAs QD solar cells. The short circuit current density and open circuit voltages of solar cells with and without dots measured under identical conditions are 1.29 mA/ cm 2 , 0.37 V and 1.17 mA/ cm 2 , 0.6 V, respectively.
We report optical, electrical, and spectral response characteristics of three-stack InAs∕GaAs quantum dot solar cells with and without GaP strain compensation (SC) layers. The short circuit current density, open circuit voltage, and external quantum efficiency of these cells under air mass 1.5G at 290mW∕cm2 illumination are presented and compared with a GaAs control cell. The cells with SC layers show superior device quality, confirmed by I-V and spectral response measurements. The quantum dot solar cells show an extended photoresponse compared to the GaAs control cell. The effect of the SC layer thickness on device performance is also presented.
In this work, we study hybrid solar cells based on poly(3-hexylthiophene)-coated GaAs nanopillars grown on a patterned GaAs substrate using selective-area metal organic chemical vapor deposition. The hybrid solar cells show extremely low leakage currents (I≅45 nA @−1V) under dark conditions and an open circuit voltage, short circuit current density, and fill factor of 0.2 V, 8.7 mA/cm2, and 32%, respectively, giving a power conversion efficiency of η=0.6% under AM 1.5 G illumination. Surface passivation of the GaAs results in further improvement, yielding η=1.44% under AM 1.5 G illumination. External quantum efficiency measurements of these polymer/inorganic solar cells are also presented.
There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm2. In addition, the cells on GaAs substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.
Interfacial
charge transfer is ubiquitous in many chemical and
physical processes and can occur on ultrafast time scales of femtoseconds
to picoseconds. Probing dynamics on such time scales necessitates
the use of ultrafast laser spectroscopies, but signatures of interfacial
charge transfer can be overwhelmed by the signal from bulk materials.
This problem may be alleviated in second-harmonic generation, which
can be specifically sensitive to interfacial charge transfer if other
bulk and interfacial contributions to the measured second-harmonic
signal can be resolved. We report the development of a femtosecond
spectral interferometry technique for second-harmonic generation with
time, energy, and phase resolution. Using the model systems of a passivated
GaAs(100) surface and copper phthalocyanine/GaAs(100) interface, we
demonstrate the application of this technique in unveiling the rich
dynamics of band renormalization, charge carrier motion, and interfacial
charge transfer, all induced by across-bandgap optical excitation
of the semiconductor.
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