Suppression of thermal carrier escape and efficient photo-carrier generation by two-step photon absorption in InAs quantum dot intermediate-band solar cells using a dot-in-well structure

Asahi, Shigeo; Teranishi, Haruyuki; Kasamatsu, Naofumi; Kada, Tomoyuki; Kaizu, Toshiyuki

doi:10.1063/1.4892826

Cited by 31 publications

(33 citation statements)

References 15 publications

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“…In this wavelength region, the EQE signal also shows a gradual decrease with increasing wavelength because the optical absorption coefficient becomes small with increasing wavelength. In the near-IR wavelength region below the bandgap of GaAs, the EQE signal decreases drastically and shows a small structure at 912 nm that can be attributed to thermally excited carriers from the deep quantized states of the InAs wetting layer2140.…”

Section: Resultsmentioning

confidence: 99%

“…According to ideal theoretical predictions, the IBSC is expected to exhibit extremely high conversion efficiency, >60%, under the maximum concentration and 48.2% under one-sun irradiation5. Substantial progress has been made in this field101112131415161718192021222324252627 since Luque and Martí have proposed this concept of IBSC in 1997 (ref. 5).…”

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confidence: 99%

“…Obviously, carriers in the IB that have long lifetimes have a greater capacity to improve the TPU efficiency because the absorption coefficient between the CB and IB is proportional to the electron density in the initial state of the intraband transition. However, the application of an additional infrared (IR) light corresponding to 40 suns has been observed to improve the external quantum efficiency (EQE) by <0.5% (refs 21, 22). The further enhancement of TPU is essential to accomplish high conversion efficiency above 50% under sunlight concentration.…”

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confidence: 99%

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Two-step photon up-conversion solar cells

et al. 2017

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Reducing the transmission loss for below-gap photons is a straightforward way to break the limit of the energy-conversion efficiency of solar cells (SCs). The up-conversion of below-gap photons is very promising for generating additional photocurrent. Here we propose a two-step photon up-conversion SC with a hetero-interface comprising different bandgaps of Al0.3Ga0.7As and GaAs. The below-gap photons for Al0.3Ga0.7As excite GaAs and generate electrons at the hetero-interface. The accumulated electrons at the hetero-interface are pumped upwards into the Al0.3Ga0.7As barrier by below-gap photons for GaAs. Efficient two-step photon up-conversion is achieved by introducing InAs quantum dots at the hetero-interface. We observe not only a dramatic increase in the additional photocurrent, which exceeds the reported values by approximately two orders of magnitude, but also an increase in the photovoltage. These results suggest that the two-step photon up-conversion SC has a high potential for implementation in the next-generation high-efficiency SCs.

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Section: Resultsmentioning

confidence: 99%

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Two-step photon up-conversion solar cells

et al. 2017

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“…6 To enable quasi-Fermi level splitting between IB and CB, thermal escape should be suppressed. Therefore, although experimental observation of the second photon absorption has been observed at both low temperature [9][10][11] and room temperature, [12][13][14] the voltage preservation so far has only been shown at low temperature. 15,16 To increase the a) Now at Finisar Corporation.…”

Section: Introductionmentioning

confidence: 99%

Effect of electric field on carrier escape mechanisms in quantum dot intermediate band solar cells

Polly

Hellstroem

Slocum

et al. 2017

Journal of Applied Physics

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Carrier escape and recombination from quantum dot (QD) states reduce the probability of two-step photon absorption (TSPA) by decreasing the available carrier population in the intermediate band (IB). In order to optimize the second photon absorption for future designs of quantum dot embedded intermediate band solar cells, the presented study combined the results of simulations and experiments to quantify the effect of electric field on the barrier height and the carrier escape from the QDs in InAs/GaAs quantum dot solar cells with five-layer QD superlattices. The electric field dependent effective barrier heights for ground state electrons were calculated using eight band kÁp theory at short circuit conditions. With an increase in electric field surrounding the QDs from 5 kV/cm to 50 kV/cm, the effective barrier height of the ground state electrons was reduced from 147 meV to 136 meV, respectively. Thus, the increasing electric field not only exponentially enhances the ground state electron tunneling rate (effectively zero at 5 kV/cm and 7.9 Â 10 6 s À1 at 50 kV/cm) but also doubles the thermal escape rate (2.2 Â 10 11 s À1 at 5 kV/cm and 4.1 Â 10 11 s À1 at 50 kV/cm). Temperature-dependent external quantum efficiency measurements were performed to verify that the increasing electric field decreases the effective barrier height. Additionally, the electric field dependent radiative lifetimes of the ground state were characterized with time-resolved photoluminescence experiments. This study showed that the increasing electric field extended the radiative recombination lifetime in the ground state of the QDs as a consequence of the reduced wave-function overlap between the electrons and holes. The balance of carrier escape and recombination determines the probability of TSPA. Published by AIP Publishing.

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“…EQE spectra below the edge of DWELL-IBSC (solid line) and QD-IBSC (broken line). The horizontal axis indicates the energy difference from the band edge 8). ΔEQE (IR on − IR off ) a) EQE spectra below the band edge of Al 0.3 Ga 0.7 As with and without the IR laser.…”

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Analyses of Saturable Behavior of Two-Step Photoexcitation in InAs/GaAs/Al<sub>0.3</sub>Ga<sub>0.7</sub>As Intermediate-Band Solar Cells

重雄¹,

陽之²,

直史³

et al. 2015

J. Soc. Mat. Sci., Japan

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We systematically studied two-step photocurrent generation as functions of the excitation intensities for the interband and inter-subband transitions in an InAs/GaAs/Al 0.3 Ga 0.7 As dot-in-well (DWELL) intermediate-band solar cell. The two-step photoexcitation current shows saturation as the inter-band excitation intensity becomes strong, and we found that the inter-band excitation intensity showing the current saturation strongly depends on the inter-subband excitation intensity. To interpret the current-saturation behavior, we proposed a model and carried out theoretical simulation. Simulated results excellently reproduce the experimental observations. It has been claried that the photocurrent saturation is caused by lling the intermediate states with electrons. Furthermore, the recombination lifetime in DWELL was pointed out to be extremely long. Our results suggest that this carrier lifetime is an important key to realize strong enhancement of two-step photoexcitation.

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Suppression of thermal carrier escape and efficient photo-carrier generation by two-step photon absorption in InAs quantum dot intermediate-band solar cells using a dot-in-well structure

Cited by 31 publications

References 15 publications

Two-step photon up-conversion solar cells

Two-step photon up-conversion solar cells

Effect of electric field on carrier escape mechanisms in quantum dot intermediate band solar cells

Analyses of Saturable Behavior of Two-Step Photoexcitation in InAs/GaAs/Al<sub>0.3</sub>Ga<sub>0.7</sub>As Intermediate-Band Solar Cells

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