Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells

Stolterfoht, Martin; Wolff, Christian; Marquez, J.A.; Zhang, Shanshan; Hages, Charles J.; Rothhardt, Daniel; Albrecht, Steve; Burn, Paul L.; Meredith, Paul; Unold, Thomas; Neher, Dieter

doi:10.1038/s41560-018-0219-8

Cited by 837 publications

(927 citation statements)

References 51 publications

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“…[33] Radiative recombination happens in a very short time, and normally appears as a power-law decay in the TRPL measurement, whereas the non-radiative recombination by monomolecular shows a monoexponential decay in the TRPL measurement. The second role played by ESM/HSM has been confirmed by Stolterfoht et al [34] who compared a range of ESMs and HSMs using the TRPL and absolute PL spectra measurement. [30] When the perovskite film is deposited adjacent to an ESM or HSM, the interpretation of TRPL data can be more complicated.…”

Section: Device Characterizationmentioning

confidence: 79%

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Rationalizing the Molecular Design of Hole‐Selective Contacts to Improve Charge Extraction in Perovskite Solar Cells

Wang

Mosconi

Wolff

et al. 2019

Advanced Energy Materials

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Two new hole selective materials (HSMs) based on dangling methylsulfanyl groups connected to the C‐9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro‐OMeTAD molecule, these HSMs (referred as FS and DFS) share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency (up to 18.6%) is achieved by using the new HSMs in suitable perovskite solar cells. Time‐resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM/perovskite interface with respect to Spiro‐OMeTAD, which is reflected in higher photocurrents exhibited by DFS/FS‐integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS/FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro‐OMeTAD. Importantly, the low‐cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cells.

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Section: Device Characterizationmentioning

confidence: 79%

“…The more efficient in charge extraction, the more efficient in quenching of PL intensity. [34,35] The second role played by ESM/HSM has been confirmed by Stolterfoht et al [34] who compared a range of ESMs and HSMs using the TRPL and absolute PL spectra measurement.…”

Section: Device Characterizationmentioning

confidence: 86%

Rationalizing the Molecular Design of Hole‐Selective Contacts to Improve Charge Extraction in Perovskite Solar Cells

Wang

Mosconi

Wolff

et al. 2019

Advanced Energy Materials

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“…While the absolute locations of E F,e and E F,h are generally not accessible, the QFLS can be determined directly by means of absolute PL measurements . This methodology has been proven to be an efficient approach for quantifying recombination losses in the neat perovskite, multilayer assemblies or even complete perovskite solar cells …”

Section: Theorymentioning

confidence: 99%

“…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 for nonradiative recombination in neat perovskite layers . More recently, several studies have additionally highlighted the thorny problematic of the interfaces between the perovskite and charge transport layers in the actual device, due to the fast nonradiative recombination of carriers at or across these interfaces . Therefore, a detailed understanding of the losses and the underlying physical processes is essential in order to exploit the full potential of these materials in solar cells.…”

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

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349

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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“…The increase in J sc can be attributed to the decrease in the series resistance as well as increase in the absorption at the active layer due to the near‐field enhancement and LSPR effect of the metal NPs . The recombination in the active layer and at the interface causes a loss in V oc . Moreover, reduced shunt resistance caused a decrease in the V oc .…”

Section: Resultsmentioning

confidence: 99%

Effect of Plasmonic Ag Nanoparticles on the Performance of Inverted Perovskite Solar Cells

et al. 2019

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Recently, perovskite solar cells (PSCs) have attracted phenomenal research interest due to their potential as the next‐generation photovoltaics. Despite rapid development in this field, further increasing their power conversion efficiency (PCE) remains a critical issue for the commercialization of PSCs. Herein, the application of Ag nanoparticle (NP) layers via vapor‐phase deposition onto perovskite active layers is investigated. The formation of unique, crescent‐shaped Ag NPs is confirmed by scanning electron microscopy (SEM), which shows that the NPs self‐assemble along the grain boundaries of perovskite, leading to their unique shape. The PCE for devices incorporating an optimized size of Ag NPs of 79 ± 6 nm increase from 11.63% to 13.46% with an improvement factor of 15.74%. The increase in PCE is can be attributed to an increase in short‐circuit current density (Jsc) that is assigned to an increase in optical path length and absorption. NPs exhibit the ability to increase the optical path length of photons in the device due to the near‐field and far‐field enhancement (plasmonic scattering) and consequently may act to improve the photon‐to‐electron conversion efficiency (ΔIPCE) and PCE of PSCs. Moreover, ultraviolet photoelectron spectroscopy reveals a decrease in hole injection barrier (ϕh), which also contributes to enhanced performance.

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Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells

Cited by 837 publications

References 51 publications

Rationalizing the Molecular Design of Hole‐Selective Contacts to Improve Charge Extraction in Perovskite Solar Cells

Rationalizing the Molecular Design of Hole‐Selective Contacts to Improve Charge Extraction in Perovskite Solar Cells

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

Effect of Plasmonic Ag Nanoparticles on the Performance of Inverted Perovskite Solar Cells

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