Effects of electric field on thermal and tunneling carrier escape in InAs/GaAs quantum dot solar cells

Dai, Yushuai; Polly, Stephen J.; Hellström, Staffan; Driscoll, Kristina; Forbes, David V.; Hubbard, Seth M.; Roland, Paul J.; Ellingson, Randy J.

doi:10.1117/12.2040153

Cited by 5 publications

(4 citation statements)

References 16 publications

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“…Optically promoted intersubband escape of carriers by absorption of infrared photons may be important at lower temperatures, for which thermal and tunneling escape events become significantly reduced [11]. Tunneling-assisted escape can be dominant in the shallower energy levels for high local electric field intensities (>50 kV cm −1 ) [47], a limiting value very much above the electric field profiles observed in our simulations. Capture and relaxation time constants are determined from experimental data [27], whereas the thermal escape times are calculated from the rate equations, by assuming that the structure reaches a quasi-Fermi equilibrium in the absence of recombination and photogeneration processes [48], leading to the expression…”

Section: Numerical Modelmentioning

confidence: 54%

Dependence of quantum dot photocurrent on the carrier escape nature in InAs/GaAs quantum dot solar cells

Cédola

Cappelluti

Gioannini

2016

Semicond. Sci. Technol.

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This paper presents a theoretical study of the effect of the nature of the carrier escape from quantum dots (QDs) on the performance of InAs/GaAs QD solar cells (QDSCs), based on numerical simulations. Excitonic and non-excitonic dynamics of electrons and holes are considered in the modeling, by assuming identical or separate time constants for the intersubband carrier transfer processes in the ground and excited states. It is shown that the excitonic capture and escape allow us to explain the non-additive characteristic of the QD photocurrent, observed when the total photocurrent of the cell is much lower than the sum of the photocurrents contributed separately by the barrier and the nanostructures. This behavior is practically eliminated in the non-excitonic case. The correlated dynamics under the nonexcitonic scenario is analyzed by calculating the device sensitivity to small changes introduced in the escape time of electrons. It is stated that the non-variation of the QD photocurrent with this parameter could be interpreted as a consequence of either a correlated electron-hole escape from QDs, or a dominant recombination over the other involved processes. The ideality factor of the different QDSCs studied is also calculated from simulations under both concentrated sunlight and dark conditions. The obtained results are in line with experimental measurements published in the literature.

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Section: Numerical Modelmentioning

confidence: 54%

Dependence of quantum dot photocurrent on the carrier escape nature in InAs/GaAs quantum dot solar cells

Cédola

Cappelluti

Gioannini

2016

Semicond. Sci. Technol.

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“…For further understanding of the UV responses and device performances, the tunneling property within the Si-QD layer should be considered. Yushuai et al reported that the tunneling rate decreases when an insufficient electric filed is formed in QD solar cell [24]. Accordingly, to confirm whether a sufficient field is formed during the device operation, we carried out the EQE measurement in the UV region (300-400 nm) by applying an external bias voltage from 0 to −1 V shown in figure 8.…”

Section: Resultsmentioning

confidence: 99%

Ultraviolet responses of a heterojunction Si quantum dot solar cell

et al. 2016

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We investigated the ultraviolet (UV) responses of a heterojunction Si quantum dot (QD) solar cell consisting of p-type Si-QDs fabricated on a n-type crystalline Si (p-Si-QD/n-c-Si HJSC). The UV responses were compared with a conventional n-type crystalline Si solar cell (n-c-Si SC). The external and internal quantum efficiency results of the p-Si-QD/n-c-Si HJSC exhibited a clear enhancement in the UV responses (300-400 nm), which was not observed in the n-c-Si SC. Based on the results of the cell reflectance and bias-dependent responses, we expect that almost all UV responses occur in the p-Si-QD layer, and the generated carriers can be transported via the Si-QD layer due to the formation of a sufficient electric filed. As a result, a high power conversion efficiency of 14.5% was achieved from the p-Si-QD/n-c-Si HJSC. By reducing the thickness of the n-Si substrate from 650 μm to 300 μm, more enhanced power conversion efficiency of 14.8% was obtained which is the highest value among the reported Si-QD based solar cells to date.

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“…The escape of holes, because of their shallow confinement, is essentially thermally-driven, whereas a more complex picture may underlie the electrons escape. In fact, thermal escape is usually dominant for the escape from GS, whereas tunnelling can be significant for the higher energy states under high electric fields, on the order at least of a few tens of kV/cm as reported, for example, in [9,16]. Clearly, the relative strength of thermal-assisted or tunnelling-assisted mechanisms on the escape rate is very dependent on the QD energy levels and device structure as well.…”

Section: Model Overviewmentioning

confidence: 96%

“…However, while a significant amount of experimental and theoretical works has focused on the investigation of carrier dynamics in QD lasers and semiconductor optical amplifiers [6], [7], [8], less effort has been put on studying carrier dynamics in QD solar cells, with emphasis on evaluating carrier lifetime in QD states [4] and carrier escape mechanisms [9]. Capture dynamics and intersubband processes in the cell under forward bias still remain to be investigated.…”

Section: Introductionmentioning

confidence: 99%

Impact of carrier dynamics on the photovoltaic performance of quantum dot solar cells

Gioannini¹,

Cédola

Cappelluti³

2015

IET Optoelectronics

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The paper presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of QD kinetics within a drift-diffusion formalism. Steady-state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs.

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Effects of electric field on thermal and tunneling carrier escape in InAs/GaAs quantum dot solar cells

Cited by 5 publications

References 16 publications

Dependence of quantum dot photocurrent on the carrier escape nature in InAs/GaAs quantum dot solar cells

Dependence of quantum dot photocurrent on the carrier escape nature in InAs/GaAs quantum dot solar cells

Ultraviolet responses of a heterojunction Si quantum dot solar cell

Impact of carrier dynamics on the photovoltaic performance of quantum dot solar cells

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