Open circuit voltage recovery in quantum dot solar cells: a numerical study on the impact of wetting layer and doping

Cappelluti, Federica; Khalili, Arastoo; Gioannini, Mariangela

doi:10.1049/iet-opt.2016.0069

Cited by 6 publications

(7 citation statements)

References 21 publications

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“…Several issues need to be overcome in QDSCs, such as to avoid an important reduction of the open-circuit voltage (V OC ) that leads to a drop in the efficiency in comparison to their single junction GaAs SC counterparts [3,12]. It is said that the key prerequisite for improvement of the output voltage is the suppression of photoelectron capture from the conduction band into QD states which mainly occurs through the extended wetting layer (WL) state [13,14]. Certainly, it is demonstrated that the large phase volume of WL plays a major role in this V OC reduction [15], so QD properties can be radically altered if WL states are non-existent.…”

Section: Introductionmentioning

confidence: 99%

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

et al. 2022

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Recently, thin AlAs capping layers (CLs) on InAs quantum dot solar cells (QDSCs) have been shown to yield better photovoltaic efficiency compared to traditional QDSCs. Although it has been proposed that this improvement is due to the suppression of the capture of photogenerated carriers through the wetting layer (WL) states by a de-wetting process, the mechanisms that operate during this process are not clear. In this work, a structural analysis of the WL characteristics in the AlAs/InAs QD system with different CL-thickness has been made by scanning transmission electron microscopy techniques. First, an exponential decline of the amount of InAs in the WL with the CL thickness increase has been found, far from a complete elimination of the WL. Instead, this reduction is linked to a higher shield effect against QD decomposition. Second, there is no compositional separation between the WL and CL, but rather single layer with a variable content of InAlGaAs. Both effects, the high intermixing and WL reduction cause a drastic change in electronic levels, with the CL making up of 1–2 monolayers being the most effective configuration to reduce the radiative-recombination and minimize the potential barriers for carrier transport.

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Section: Introductionmentioning

confidence: 99%

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

et al. 2022

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“…The electron and hole confinement energy in the QD levels (e.g., for the GS level, ∆E e GS and ∆E h GS in Fig. 2) is estimated by assuming that 80% of the difference between the GaAs band gap (E g,B = 1.424 eV) and the QD level energy gap is allocated to the conduction band [40,39]. Since the thermally-dominated escape rate depends on the confinement energy, this implies that holes have a markedly faster dynamics than electrons.…”

Section: Electrical Modelmentioning

confidence: 99%

“…Thus, escape time constants are derived from capture and relaxation scattering times based on the argument of detailed balance at thermal equilibrium [21]. This modeling approach allows to single out the impact on the cell photovoltaic behavior of different and interplaying physical mechanisms, such as QD kinetics [23,38,39], non radiative recombination [21], and photon losses (by proper coupling with a suitable optical model) and thus it is very well suited for the interpretation of experimental results and the investigation of novel design solutions.…”

Section: Electrical Modelmentioning

confidence: 99%

Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off

Cappelluti

Kim

Eerden³

et al. 2018

Solar Energy Materials and Solar Cells

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We report thin-film InAs/GaAs quantum dot (QD) solar cells with n − i − p + deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-inch wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavelength range, the ELO QD cell perfectly preserves the current collection efficiency of the baseline single-junction ELO cell. We demonstrate by full-wave optical simulations that integrating a micro-patterned diffraction grating in the ELO cell rearside provides more than tenfold enhancement of the near-infrared light harvesting by QDs. Experimental results are thoroughly discussed with the help of physics-based simulations to single out the impact of QD dynamics and defects on the cell photovoltaic behavior. It is demonstrated that non radiative recombination in the QD stack is the bottleneck for the open circuit voltage (V oc ) of the reported devices. More important, our theoretical calculations demonstrate that the V oc offest of 0.3 V from the QD ground state identified by Tanabe et al., 2012, from a collection of experimental data of high quality III-V QD solar cells is a reliable -albeit conservative -metric to gauge the attainable V oc and to quantify the scope for improvement by reducing non radiative recombination. Provided that material quality issues are solved, we demonstrate -by transport and rigorous electromagnetic simulations -that light-trapping enhanced thin-film cells with twenty InAs/GaAs QD layers reach efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible.

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“…[25]), making the QD carrier lifetime largely dominated by the QD radiative lifetime. Moreover, the open-circuit voltage (V oc ) penalty in thermally limited QDSCs is dominated by the ratio between carrier lifetime in the barrier and carrier lifetime in QDs [27], the last one being the net result of the competing processes of capture/relaxation/recombination through the QDs-from the one hand-and escape from the QD bound states and electric-field-driven sweep out through the extended states-from the other hand. Thus, at least in In(Ga)As/GaAs QDs and under nonconcentration operation, capture/relaxation times can be reasonably treated as constant parameters, neglecting their carrier density dependence and the possible electric-field dependence due to tunneling mechanisms.…”

Section: Modelmentioning

confidence: 99%

Physics-Based Modeling and Experimental Study of Si-Doped InAs/GaAs Quantum Dot Solar Cells

Cédola¹,

Kim

Tibaldi

et al. 2018

International Journal of Photoenergy

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This paper presents an experimental and theoretical study on the impact of doping and recombination mechanisms on quantum dot solar cells based on the InAs/GaAs system. Numerical simulations are built on a hybrid approach that includes the quantum features of the charge transfer processes between the nanostructured material and the bulk host material in a classical transport model of the macroscopic continuum. This allows gaining a detailed understanding of the several physical mechanisms affecting the photovoltaic conversion efficiency and provides a quantitatively accurate picture of real devices at a reasonable computational cost. Experimental results demonstrate that QD doping provides a remarkable increase of the solar cell open-circuit voltage, which is explained by the numerical simulations as the result of reduced recombination loss through quantum dots and defects.

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Open circuit voltage recovery in quantum dot solar cells: a numerical study on the impact of wetting layer and doping

Cited by 6 publications

References 21 publications

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off

Physics-Based Modeling and Experimental Study of Si-Doped InAs/GaAs Quantum Dot Solar Cells

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