Probing surface recombination velocities in semiconductors using two-photon microscopy

Gaury, Benoit; Haney, Paul M.

doi:10.1063/1.4944597

Cited by 21 publications

(8 citation statements)

References 21 publications

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“…[ 14–16 ] When carrier diffusion length exceeds dimensions of the focused laser beam, carrier dynamics can also be impacted by the lateral drift and diffusion. [ 17–20 ] As a result, currently there are no accepted analytical methods for microscopic carrier lifetime analysis in solar cells. [ 19 ] Here, we apply spectroscopic and microscopic measurements to the same samples and establish conditions when microscopic and spectroscopic characterization can produce comparable results, thus validating microscopic carrier lifetime analysis for thin‐film solar cells.…”

Section: Introductionmentioning

confidence: 99%

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

2021

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Due to the lowest‐cost and best reliability, CdTe solar cells are the leading thin‐film photovoltaic technology. Increasing open‐circuit voltage by reducing recombination represents the most promising path toward further improvements. Analysis is needed to identify limitations that cause efficiency losses. To achieve this goal for Cu‐doped CdSe/CdTe solar cells, time‐resolved spectroscopy and microscopy are developed and applied. Recombination lifetimes and radiative efficiency identify that defect‐mediated recombination is the dominant voltage loss mechanism. When carrier lifetimes are averaged over many crystalline grains, they increase from 180 to 430 ns when Al2O3 is applied to the back contact. The quasi‐Fermi‐level splitting correspondingly increases from 880–905 to 906–931 mV, indicating a pathway to overcome the long‐standing 900 mV voltage limitation. However, the dominant recombination losses are attributed to the absorber bulk. From microscopic carrier lifetime measurements, it is identified that space charge fields due to charged grain boundaries (GBs) lead to recombination in the CdTe absorber bulk. At high injection, GB space charge fields are screened, but that occurs above 1 Sun excitation conditions. Alloying with selenium in the near‐interface CdSeTe absorber region reduces GB losses and is identified as one of the factors leading to high radiative and power conversion efficiency.

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Section: Introductionmentioning

confidence: 99%

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

2021

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“…Indeed, the diffusion phenomenon is visible at high frequency and limits the recombination rate at the surface and so the corner frequency. From [18] and [19] we have the following equations :…”

Section: Iii3 With Srvmentioning

confidence: 99%

Analytical model of the modulated photoluminescence in semiconductor materials

Moron¹,

Bérenguier²,

Alvarez³

et al. 2021

J. Phys. D: Appl. Phys.

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Modulated photoluminescence (MPL) is an optoelectronic characterization technique of semiconductor materials. Going to high frequencies enables one to characterize fast phenomena, and so materials with a short lifetime such as chalcogenides or III–V absorbers. Some typical signatures have already been experimentally observed. However, physical mechanisms and quantitative analyses are not well understood yet. Here, using both an analytical approach and a full numerical modeling, we study how the energy position of a defect level, its electron and hole capture cross sections, its density, influence the frequency dependence of the MPL phase. We show that quantitative information can be extracted. We also study the effect of additional surface recombination, and of non homogeneities created by carrier generation profiles or asymmetric top surface and bottom surface recombination velocities, where diffusion of the carriers plays a role and can be limiting at high frequency. Finally we apply our model to an experimental result to extract defect parameters of the sample. Our analysis highlights the usefulness of MPL and the importance of having a proper modeling of the experiment.

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“…We analyze how the carrier recombination and diffusion away from the generation/collection region affect the PL intensity. We compare these results to the limiting case of a point source whose PL decay reads [8]…”

Section: Measurementsmentioning

confidence: 99%

“…As a result, experimentally, in the long time limit a mono-exponential fit should suffice to determine the bulk lifetime τ . Comparisons with experimental data can be found in [8].…”

Section: Measurementsmentioning

confidence: 99%

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Minority-carrier dynamics in semiconductors probed by two-photon microscopy

Gaury

Haney

2016

2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC)

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Abstract-Two-photon time-resolved photoluminescence has been recently applied to various semiconductor devices to determine carrier lifetime and surface recombination velocities. So far the theoretical modeling activity has been mainly limited to the commonly used one-photon counterpart of the technique. Here we provide the analytical solution to a 3D diffusion equation that describes two-photon microscopy in the low-injection regime. We focus on a system with a single buried interface with enhanced recombination, and analyze how transport, bulk and surface recombinations influence photoluminescence decays. We find that bulk measurements are dominated by diffusion at short times and by bulk recombination at long times. Surface recombination modifies bulk signals when the optical spot is less than a diffusion length away from the probed interface. In addition, the resolution is increased as the spot size is reduced, which however makes the signal more sensitive to diffusion.Index Terms-Two-photon microscopy, carrier lifetime, surface recombination velocity.

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Probing surface recombination velocities in semiconductors using two-photon microscopy

Cited by 21 publications

References 21 publications

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

Identification of Recombination Losses in CdSe/CdTe Solar Cells from Spectroscopic and Microscopic Time‐Resolved Photoluminescence

Analytical model of the modulated photoluminescence in semiconductor materials

Minority-carrier dynamics in semiconductors probed by two-photon microscopy

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