Beyond Bulk Lifetimes: Insights into Lead Halide Perovskite Films from Time-Resolved Photoluminescence

Staub, Florian; Hempel, Hannes; Hebig, Jan-Christoph; Mock, J. B.; Paetzold, Ulrich W.; Rau, Uwe; Unold, Thomas; Kirchartz, Thomas

doi:10.1103/physrevapplied.6.044017

Cited by 213 publications

(261 citation statements)

References 65 publications

(91 reference statements)

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“…It is well established that the QFLS of state‐of‐the‐art perovskite solar cells still lies well below the QFLS rad . According to Equation , this is due to nonradiative losses, e.g., nonradiative recombination in the bulk and at interfaces and/or parasitic absorption . A possible way to look at the nature of these losses is to study the ideality factor .…”

Section: Resultsmentioning

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

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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%

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

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307

364

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“…This behavior rules out radiative and Auger recombination limits for Δn(t), where τ varies as a function of Δn. [3,44] Additionally, Shockley-Read-Hall (SRH) recombination is expected to be dependent upon the injection level, with the decay time τ ≈ τ n0 in low injection and τ ≈ τ n0 + τ p0 in high injection, [1,26] where τ n0 and τ p0 are the SRH minority and majority carrier lifetimes, respectively; an intensity-independent decay time would only be expected for τ p0 ≪ τ n0 . Intensity-dependent minority carrier lifetimes consistent with SRH recombination have been reported for CIGSe.…”

Section: Intensity-dependent and Spectrally Resolved Trplmentioning

confidence: 99%

Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials

Hages

Redinger

Levcenko

et al. 2017

Advanced Energy Materials

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Time‐resolved photoluminescence (TRPL) is a powerful characterization technique to study carrier dynamics and quantify absorber quality in semiconductors. The minority carrier lifetime, which is critically important for high‐performance solar cells, is often derived from TRPL analysis. However, here it is shown that various nonideal absorber properties can dominate the TRPL signal making reliable extraction of the minority carrier lifetime not possible. Through high‐resolution intensity‐, temperature‐, voltage‐dependent, and spectrally resolved TRPL measurements on absorbers and devices it is shown that photoluminescence (PL) decay times for kesterite materials are dominated by minority carrier detrapping. Therefore, PL decay times do not correspond to the minority carrier lifetime for these materials. The lifetimes measured here are on the order of hundreds of picoseconds in contrast to the nanosecond lifetimes suggested by the decay curves. These results are supported with additional measurements, device simulation, and comparison with recombination limited PL decays measured on Cu(In,Ga)Se2. The kesterite material system is used as a case study to demonstrate the general analysis of TRPL data in the limit of various measurement conditions and nonideal absorber properties. The data indicate that the current bottleneck for kesterite solar cells is the minority carrier lifetime.

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“…when is reduced. The approach proposed here will be useful both for computational materials screening in photovoltaics but also for experimental materials screening where properties of absorber layers are used to determine the efficiency potential of a certain material class [20,56,57].…”

Section: Figure 1: the Sq-limit Is Derived Using An Approximation Thamentioning

confidence: 99%

“…The internal luminescence quantum efficiency is a complex interplay between energy levels in the material, defects, and kinetics in the device. It is therefore very challenging to determine computationally but it might be possible to determine it experimentally without having to fabricate devices [57]. Approaches for first-principles calculations of non-radiative recombination rates due to point defects are emerging [67][68][69] and could provide in the future at least an estimate of the upper limit of under idealized situations.…”

Section: Recipe To Calculate Efficiency Limitsmentioning

confidence: 99%

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

et al. 2017

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The success of recently discovered absorber materials for photovoltaic applications has been generating an increasing interest in systematic materials screening over the last years. However, the key for a successful materials screening is a suitable selection metric that goes beyond the Shockley-Queisser theory that determines the thermodynamic efficiency limit of an absorber material solely by its band gap energy. In this work, we develop a selection metric to quantify the potential photovoltaic efficiency of a material. Our approach is compatible with detailed balance and applicable in computational and experimental materials screening. We use the complex refractive index to calculate radiative and nonrradiative efficiency limits and the respective optimal thickness in the high mobility limit. We compare our model to the widely applied selection metric by Yu and Zunger [Phys Rev Lett 108, 068701 (2012)] with respect to their dependency on thickness, internal luminescence quantum efficiency and refractive index. Finally the model is applied to complex refractive indices calculated via electronic structure theory.2

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Beyond Bulk Lifetimes: Insights into Lead Halide Perovskite Films from Time-Resolved Photoluminescence

Cited by 213 publications

References 65 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

Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

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