Detailed-balance power conversion limits of nanocrystal-quantum-dot solar cells in the presence of carrier multiplication

Klimov, Victor I.

doi:10.1063/1.2356314

Cited by 197 publications

(164 citation statements)

References 14 publications

(22 reference statements)

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“…[12][13][14][15][16][17] In view of these recent developments in nonequilibrium thermodynamics as well as in nanotechnologies, we propose in this paper to investigate the performance of a single nanosized photoelectric device. The discrete nature of its energy levels is essential to provide strong coupling and, thus, high efficiencies.…”

Section: ͑1͒mentioning

confidence: 99%

“…[7][8][9][10][11] A similar tendency toward the development of nanostructured materials and even single nanosized devices also occurred in photovoltaic applications. [12][13][14][15][16][17] In view of these recent developments in nonequilibrium thermodynamics as well as in nanotechnologies, we propose in this paper to investigate the performance of a single nanosized photoelectric device. The discrete nature of its energy levels is essential to provide strong coupling and, thus, high efficiencies.…”

Section: ͑1͒mentioning

confidence: 99%

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Reaching optimal efficiencies using nanosized photoelectric devices

2009

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We study the thermodynamic efficiency of a nanosized photoelectric device and show that at maximum power output, the efficiency is bounded from above by a result closely related to the Curzon-Ahlborn efficiency. We find that this upper bound can be attained in nanosized devices displaying strong coupling between the generated electron flux and the incoming photon flux from the sun. DOI: 10.1103/PhysRevB.80.235122 PACS number͑s͒: 05.70.Ln, 05.30.Ϫd, 73.50.Pz Understanding and controlling the mechanisms that determine the efficiency of photoelectric devices is of fundamental importance in the quest for efficient and clean sources of energy. Thermodynamically speaking, these devices are driven by the temperature difference between a hot reservoir ͑sun, temperature T s ͒ and a cold reservoir ͑earth, ambient temperature T͒. Therefore, like any heat engine, the efficiency at which the conversion of radiation into electrical energy takes place has a universal upper bound given by the Carnot efficiency ͑1͒Although this result has fundamental theoretical implications, it is of poor practical use since it is only reached when the device is operating under reversible conditions. Hence the generated power, defined as the output energy divided by the ͑infinite͒ operation time, goes to zero. In realistic circumstances of finite power output, the efficiency will necessarily be below the Carnot limit due to irreversible processes taking place in the device. Another source of possible efficiency decrease are energy losses within the device for example due to nonradiative recombination of charge carriers. Since the operational parameters of the device are mostly determined in such a way that a maximum power output is obtained, Curzon and Ahlborn examined in 1975 the efficiency of a Carnot cycle with a finite cycling time and, using the endoreversible approximation, found an efficiency at maximum2 This result is remarkable since it does not depend on the specific details of the system, and thus the question of universality naturally arises. Recent works [3][4][5][6][7] have indeed demonstrated that in the linear regime ͑small temperature differences, c Ӷ 1͒ the Curzon-Ahlborn efficiency is universal for so-called strongly coupled systems, where the heat and work producing fluxes are proportional. In these systems internal energy losses are absent, implying that the resulting efficiency is exclusively determined by the ͑unavoidable͒ irreversible processes occurring at finite power. Hence, at least in the linear regime, the CurzonAhlborn efficiency is indeed a universal upper bound, with a similar status as the Carnot efficiency. In the nonlinear regime, the efficiency at maximum power becomes device dependent but is again found to be highest for strongly coupled systems. Remarkably, it remains closely related to the Curzon-Ahlborn result. 6,7 While energy losses are almost unavoidable in the macroscopic world, new technological developments at the nanoscale open up the road to highly efficient devices. In thermoelectric researc...

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Section: ͑1͒mentioning

confidence: 99%

Section: ͑1͒mentioning

confidence: 99%

Reaching optimal efficiencies using nanosized photoelectric devices

2009

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“…Detailed balance limit calculations for solar cell efficiency with multiple carrier excitation have been carried out [75][76][77]. For example, the efficiency limit for single-junction cells generating up to 8 electron-hole pairs from one photon was estimated as 58% under a 1,000-sun illumination (39% for 1 sun) relative to 38% (31% for 1 sun) without multiple carrier excitation with their optimized energy bandgaps assuming E CM ~ 2E g ( Figure 13) [77].…”

Section: Utilization Of Higher Energy Photonsmentioning

confidence: 99%

A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures

Tanabe

2009

Energies

156

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Solar cells are a promising renewable, carbon-free electric energy resource to address the fossil fuel shortage and global warming. Energy conversion efficiencies around 40% have been recently achieved in laboratories using III-V semiconductor compounds as photovoltaic materials. This article reviews the efforts and accomplishments made for higher efficiency III-V semiconductor compound solar cells, specifically with multijunction tandem, lower-dimensional, photonic up/down conversion, and plasmonic metallic structures. Technological strategies for further performance improvement from the most efficient (Al)InGaP/(In)GaAs/Ge triple-junction cells including the search for 1.0 eV bandgap semiconductors are discussed. Lower-dimensional systems such as quantum well and dot structures are being intensively studied to realize multiple exciton generation and multiple photon absorption to break the conventional efficiency limit. Implementation of plasmonic metallic nanostructures manipulating photonic energy flow directions to enhance sunlight absorption in thin photovoltaic semiconductor materials is also emerging.

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“…[1][2][3][4][5][6][7][8][9] This finding is important because CM can potentially provide increased power conversion efficiency in low-cost, singlejunction photovoltaics via an enhanced photocurrent. 10,11 To obtain optimum photovoltaic power conversion efficiency using a single semiconductor material with energy gap E g , it is desirable that the CM onset energy is minimal and that the CM efficiency above the onset is as large as is allowed by energy conservation.…”

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confidence: 99%

Carrier Multiplication in InAs Nanocrystal Quantum Dots with an Onset Defined by the Energy Conservation Limit

2007

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Carrier multiplication (CM) is a process in which absorption of a single photon produces not just one but multiple electron−hole pairs (excitons). This effect is a potential enabler of next-generation, high-efficiency photovoltaic and photocatalytic systems. On the basis of energy conservation, the minimal photon energy required to activate CM is two energy gaps (2E g ). Here, we analyze CM onsets for nanocrystal quantum dots (NQDs) based upon combined requirements imposed by optical selection rules and energy conservation and conclude that materials with a significant difference between electron and hole effective masses such as III−V semiconductors should exhibit a CM threshold near the apparent 2E g limit. Further, we discuss the possibility of achieving sub-2E g CM thresholds through strong exciton−exciton attraction, which is feasible in NQDs. We report experimental studies of exciton dynamics (Auger recombination, intraband relaxation, radiative recombination, multiexciton generation, and biexciton shift) in InAs NQDs and show that they exhibit a CM threshold near 2E g .Carrier Multiplication Thresholds in Bulk and Nanocrystalline Semiconductors. It has recently been established that carrier multiplication (CM), the production of multiple excitons following absorption of a single photon of sufficient energy, is efficient within the range of solar photon energies in semiconductor nanocrystal quantum dots (NQDs). [1][2][3][4][5][6][7][8][9] This finding is important because CM can potentially provide increased power conversion efficiency in low-cost, singlejunction photovoltaics via an enhanced photocurrent. 10,11 To obtain optimum photovoltaic power conversion efficiency using a single semiconductor material with energy gap E g , it is desirable that the CM onset energy is minimal and that the CM efficiency above the onset is as large as is allowed by energy conservation.According to energy conservation, the apparent minimal photon energy that is required to activate CM (pω CM ) is simply 2E g . However, the CM thresholds observed in bulk materials are significantly larger than this value. 12,13 In bulk semiconductors, the generally accepted mechanism for multiexciton generation is impact ionization in which a highenergy electron (or a hole) transfers its energy to a valenceband electron that is excited across the energy gap. 14 The CM threshold in this case is determined not only by conservation of energy but also by conservation of translational momentum, which increases the threshold above 2E g . For example, using a free-particle approximation 15,16 and applying both energy and momentum conservation laws, one can obtain that the CM threshold is approximately 4E g (Figure 1a).In NQDs, translational momentum conservation is relaxed. Therefore, one might expect that the CM threshold could reach the 2E g limit as defined by energy conservation. However, available experimental data indicate that pω CM is still greater than twice the energy gap in such materials. For example, in PbSe and PbS NQDs, it ...

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Detailed-balance power conversion limits of nanocrystal-quantum-dot solar cells in the presence of carrier multiplication

Cited by 197 publications

References 14 publications

Reaching optimal efficiencies using nanosized photoelectric devices

Reaching optimal efficiencies using nanosized photoelectric devices

A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures

Carrier Multiplication in InAs Nanocrystal Quantum Dots with an Onset Defined by the Energy Conservation Limit

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