Hybrid perovskite films approaching the radiative limit with over 90% photoluminescence quantum efficiency

Braly, Ian L.; deQuilettes, Dane W.; Pazos-Outón, Luis M.; Burke, Sven; Ziffer, Mark E.; Ginger, David S.; Hillhouse, Hugh W.

doi:10.1038/s41566-018-0154-z

Cited by 446 publications

(473 citation statements)

References 56 publications

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“…This indicates that the metal sample holder that carries the substrate (2.5 × 2.5 cm 2 ) acts as a heat sink and it is sufficient to dissipate efficiently the heat produced by the rather small illumination spot of ≈3 × 3 mm 2 . Furthermore, from the PL spectra taken at different illumination conditions, it is possible to calculate the local temperature of the emissive volume, as presented in Figure S2C (Supporting Information). These data lack evidence for an appreciable increase in temperature when increasing the illumination intensity from 0.1 to 10 suns during the short illumination time (≈1 s).…”

Section: Resultsmentioning

confidence: 99%

“…The underlying reason for this rapid success is rooted in their high absorption coefficient, panchromatic absorption of light, long carrier diffusion length and shallow trap energy levels . The combination of these properties allows for a high photocurrent and low nonradiative recombination with exceptionally high (external) photoluminescence yields (>20%) . In principle, this would allow open‐circuit voltages ( V OC ) very close to the radiative limit (≈1.3 V for a bandgap of 1.6 eV) using already existing perovskites.…”

Section: Introductionmentioning

confidence: 99%

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On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

Caprioglio

Stolterfoht

Wolff

et al. 2019

Advanced Energy Materials

320

364

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photoluminescence yields (>20%). [5] In principle, this would allow open-circuit voltages (V OC ) very close to the radiative limit (≈1.3 V for a bandgap of 1.6 eV) using already existing perovskites. However, despite the tremendous effort devoted by the scientific community on the improvement of this solar cell technology, the experimental efficiencies are still far from the Shockely-Queisser (S.Q.) theoretical predictions of power conversion efficiency (PCE) up to 30%. [6] Specifically, in order to further improve the PCE, the effort must be focused on increasing the V OC and the fill factor (FF) through the reduction of nonradiative recombination losses. Moreover, a better understanding on the predominant energy loss mechanisms in the working device has to be accomplished.Perovskite solar cells generally consist of a 300-500 nm layer of photoactive absorber, sandwiched between two charge transporting layers that have the function of selectively transporting the photogenerated electrons (holes) to the cathode (anode). In an ideal solar cell, all photons are absorbed in the perovskite films, generating electrons and holes with unity efficiency, and-under open-circuit conditions-the only recombination channel is the radiative recombination of free electrons and holes in the same layer where they are generated. Commonly, reported values for V OC are much lower due to unwanted nonradiative recombination. During the past years, many studies have evaluated recombination in perovskites layers and suggested that defects at the perovskite surface or at grain boundaries as possible reasons Today's perovskite solar cells (PSCs) are limited mainly by their open-circuit voltage (V OC ) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity-dependent measurements of the quasi-Fermi level splitting (QFLS) and of the V OC on the very same devices, including pin-type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the V OC is generally lower than the QFLS, violating one main assumption of the Shockley-Queisser theory. This has far-reaching implications for the applicability of some well-established techniques, which use the V OC as a measure of the carrier densities in the absorber. By performing drift-diffusion simulations, the intensity dependence of the QFLS, the QFLS-V OC offset and the ideality factor are consistently explained by trap-assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the V OC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the V OC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS-V OC relation is of great importance.       J J qV n k T radiative recombination current J rad...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

Caprioglio

Stolterfoht

Wolff

et al. 2019

Advanced Energy Materials

320

364

View full text Add to dashboard Cite

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“…[50] The reported external quantum yields are as high as 60-88%. [63] Yamada et al have verified η IN = 0.85 is sufficient for intensive photon recycling. Here, the external PL QY (η EX ) of our 2D lead halide perovskite crystal is measured to be 23. is close to the value acquired from lifetime by Equation (6).…”

Section: Discussionmentioning

confidence: 99%

The Dominant Energy Transport Pathway in Halide Perovskites: Photon Recycling or Carrier Diffusion?

Gan

Wen

Chen

et al. 2019

Advanced Energy Materials

116

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applications, such as solar cells, [1][2][3][4][5][6][7] lightemitting devices (LEDs), [8][9][10] photodetectors, [11][12][13] and lasers. [14][15][16][17] Regarding the solar cells, the diffusion of photogenerated carriers and photon recycling are the two possible energy transport pathways that could affect the internal carrier dynamics and device performances. [18][19][20][21] Both processes may cause a similar influence in the external emission wavelength. Whereas, their influences on carrier lifetime, external photoluminescence (PL) quantum yield (QY), as well as opencircuit voltage (V OC ) and efficiency of the solar cells are different. [18,19] Photon recycling refers to the regeneration of an excitation via the self-reabsorption of emission from recombining photogenerated charge pairs. [18] For solar cells, generally, the performance can be boosted by a highly efficient photon recycling process. [18][19][20][21] As demonstrated previously, photon recycling will boost an additional open-cir-) according to, [20] ln 1 1where k is the Boltzmann constant, q is the elementary charge of an electron, T C is the cell temperature, η IN is the internal quantum efficiency, and p r is the probability of photon recycling. On the other hand, for LEDs, strong photon recycling implies a low outcoupling probability (η esc ), which is detrimental for external efficiency. For example, an internal PL QY lower than 95% can result in an external PL QY lower than 50%. [18] Moreover, the photophysics behind photon recycling and carrier diffusion are different. The high photon recycling efficiency generally requires a large overlapping of its PL spectrum with the absorption spectrum, a strong photon confinement, and a high-internal PL quantum yield. [18][19][20] While long carrier diffusion length is ensured by long carrier lifetime, high carrier mobility, and low defect density. [22][23][24][25][26][27] These two energy transport pathways imply different applications, therefore, it is crucial to evaluate the contributions of photon recycling and carrier diffusion in lead halide perovskites.In perovskites, very long diffusion lengths exceeding 1 µm in solution-fabricated films and hundreds of micrometers in single crystals have been reported, [22][23][24][25][26][27] enabling the radiative recombination of charge carriers at positions far away from the excitation spot. On the other hand, due to the highly efficient band-to-band transitions, large absorption coefficients, Photon recycling and carrier diffusion are the two plausible processes that primarily affect the carrier dynamics in halide perovskites, and therefore the evaluation of the performance of their photovoltaic and photonic devices. However, it is still challenging to isolate their individual contributions because both processes result in a similar emission redshift. Herein, it is confirmed that photon recycling is the dominant effect responsible for the observed redshifted emission. By applying one-and two-photon confocal emission microscopy on Ruddlesden-Popper type ...

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“…Therefore, to determine Δ μ F = 950 ± 50 mV, we fit the high‐energy side of the PL emission spectrum, as shown in the inset of Figure a . Because of potential complications with such analysis, we verified linear fit results using different excitation powers and sample irradiation time . Δ μ F is significantly higher than V OC = 880 mV in record‐efficiency solar cells, which indicates that with this absorber a higher V OC should be possible.…”

mentioning

confidence: 90%

“…Next, we determine quasi‐Fermi‐level splitting, Δ μ F . Emission at <1.35 eV precludes analysis of the full spectrum with more detailed models . Therefore, to determine Δ μ F = 950 ± 50 mV, we fit the high‐energy side of the PL emission spectrum, as shown in the inset of Figure a .…”

mentioning

confidence: 99%

Radiative Efficiency and Charge‐Carrier Lifetimes and Diffusion Length in Polycrystalline CdSeTe Heterostructures

Kuciauskas

Moseley

Ščajev

et al. 2019

Physica Rapid Research Ltrs

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CdTe‐based photovoltaics is a rapidly developing energy technology with one of the lowest levelized costs of electricity. But nonradiative Shockley–Read–Hall (SRH) recombination limits the efficiency of CdTe solar cells. Partial mitigation of bulk and grain‐boundary SRH recombination was achieved by alloying CdTe with Se, and CdSexTe1−x absorbers are used in high‐efficiency solar cells. Recently, interface recombination was significantly reduced with alumina passivation, but other properties of Al2O3/CdSexTe1−x/Al2O3 heterostructures have not yet been investigated. Herein, further progress in understanding and developing polycrystalline heterostructures with x = 0.2 is reported. It is shown that external photoluminescence quantum yield is increased to 0.2%, quasi‐Fermi‐level splitting to 950 mV, minority carrier lifetimes to 750 ns, and mobility to 100 cm2 Vs−1. Such polycrystalline CdSexTe1−x electronic characteristics match or exceed CdTe single‐crystal properties. The resulting charge‐carrier diffusion length of ≈14 μm is several times greater than the absorber thickness in test structures and in typical CdTe solar cells. Herein, with passivation and absorbers, polycrystalline CdSeTe solar cell open‐circuit voltage is increased from the current 76% of the Shockley–Queisser limit to 82%, or close to 1 V is reported.

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Hybrid perovskite films approaching the radiative limit with over 90% photoluminescence quantum efficiency

Cited by 446 publications

References 56 publications

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells

The Dominant Energy Transport Pathway in Halide Perovskites: Photon Recycling or Carrier Diffusion?

Radiative Efficiency and Charge‐Carrier Lifetimes and Diffusion Length in Polycrystalline CdSeTe Heterostructures

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