Charge Carrier Dynamics upon Sub-bandgap Excitation in Methylammonium Lead Iodide Thin Films: Effects of Urbach Tail, Deep Defects, and Two-Photon Absorption

Caselli, Valentina M.; Wei, Zimu; Ackermans, M.M.; Hutter, Eline M.; Ehrler, Bruno; Savenije, Tom J.

doi:10.1021/acsenergylett.0c02067

Cited by 52 publications

(45 citation statements)

References 39 publications

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“…In general, a smaller Urbach energy implies a lower defect density. [ 78,79 ] As shown in Figure 5d, the Urbach energy calculated from EQE spectra is 16.94 eV for the solar cell with the QD treatment and 17.45 eV for the control one, indicating notably reduced defect density in QD treated film. Additionally, the junction quality of the devices was also examined by the dark J – V measurements as shown in Figure 5e.…”

Section: Resultsmentioning

confidence: 96%

Quantum Dot Passivation of Halide Perovskite Films with Reduced Defects, Suppressed Phase Segregation, and Enhanced Stability

Duan

Yao

et al. 2021

Advanced Science

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Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr3 QDs are deposited on four types of halide perovskite films (CsPbBr3, CsPbIBr2, CsPbBrI2, and MAPbI3) and the interactions are triggered by annealing. The ions in the CsPbBr3 QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self‐assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD‐treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light‐induced phase segregation and degradation in mixed‐halide perovskite films are suppressed, and the efficiency of mixed‐halide CsPbIBr2 solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high‐quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications.

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Section: Resultsmentioning

confidence: 96%

Quantum Dot Passivation of Halide Perovskite Films with Reduced Defects, Suppressed Phase Segregation, and Enhanced Stability

Duan

Yao

et al. 2021

Advanced Science

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“… 30 Absorption and fluorescence spectra of MAPI are provided in the SI, Figure S2 and correspond to previously reported spectra. 31 …”

Section: Resultsmentioning

confidence: 99%

“…In contrast, we reported previously for MAPI/SO bilayers an enhancement in charge-carrier lifetimes, which was attributed to the fact that after charge transfer the charges are physically separated. 31 , 32 To obtain more insight into the recombination processes, we fitted the bilayers using the kinetic model of Scheme 1 completed by an additional charge transfer process to the transport layer with rate constant k h and recombination of a hole in SO with a conduction band electron with rate k e as indicated in green and blue, respectively. The TRMC traces and corresponding fits are provided in the SI, Figure S11 , for a range of intensities.…”

Section: Resultsmentioning

confidence: 99%

How Deep Hole Traps Affect the Charge Dynamics and Collection in Bare and Bilayers of Methylammonium Lead Bromide

Zhao

Caselli

Bus

et al. 2021

ACS Appl. Mater. Interfaces

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Wide-band-gap perovskites such as methylammonium lead bromide (MAPB) are promising materials for tandem solar cells because of their potentially high open-circuit voltage, which is yet still far below the maximum limit. The relatively short charge-carrier lifetimes deduced from time-resolved photoluminescence (TRPL) measurements seem in strong contrast with the long lifetimes observed with time-resolved photoconductance measurements. This is explained by a large amount of hole defect states, N T > 10 16 cm –3 , in spin-coated layers of MAPB residing at or near the grain boundaries. The introduction of hypophosphorous acid (HPA) increases the average grain size by a factor of 3 and reduces the total concentration of the trap states by a factor of 10. The introduction of HPA also increases the fraction of initially generated holes that undergo charge transfer to the selective contact, Spiro-OMeTAD (SO), by an order of magnitude. In contrast to methylammonium lead iodide (MAPI)/SO bilayers, a reduction of the carrier lifetime is observed in MAPB/SO bilayers, which is attributed to the fact that injected holes undergo interfacial recombination via these trap states. Our findings provide valuable insight into the optoelectronic properties of bromide-containing lead halide perovskites essential for designing efficient tandem solar cells.

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“…The baseline upshift reveals artificial beam scattering due to the capping layer. Furthermore, the Urbach energies corresponding to the elongated absorption tails could be obtained based on previous reports [14,23,24] and additional derivations (see Figure S3, Supplementary Note S1, and Table S1). In summary, both an increase in temperature and PbSO 4 -oleate coverage on the PQDs led to an increase in the Urbach energies.…”

Section: Effect Of Pbso 4 -Oleate Capping On Photophysical and Materials Properties Of Cspbx 3 Pqdsmentioning

confidence: 99%

Effect of PbSO4-Oleate Coverage on Cesium Lead Halide Perovskite Quantum Dots to Control Halide Exchange Kinetics

2021

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The selective control of halide ion exchange in metal halide perovskite quantum dots (PQDs) plays an important role in determining their band gap and composition. In this study, CsPbX3 (X = Cl−, Br−, and I−) PQDs were self-assembled with PbSO4-oleate to form a peapod-like morphology to selectively control halide ion exchange. Considering the distinct absorption and bright luminescence characteristics of these PQDs, in situ UV-Vis. absorption and fluorescence spectroscopies were employed to monitor the time-dependent band gap and compositional changes of the PQDs. We determined that the halide exchange in the capped PQDs is hindered—unlike the rapid anion exchange in noncapped PQDs—by a reduction in the halide exchange kinetic rate depending on the extent of coverage of the PQDs. Thus, we tracked the halide ion exchange kinetics between CsPbBr3 and CsPbI3 PQDs, depending on the coverage, using in situ UV-Vis. absorption/photoluminescence spectroscopy. We regulated the halide exchange reaction rate by varying the capping reaction temperature of the PQDs. The capping hindered the halide exchange kinetics and increased the activation energy. These results will enable the development of white LEDs, photovoltaic cells, and photocatalysts with alternative structural designs based on the divalent composition of CsPbX3 PQDs.

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Charge Carrier Dynamics upon Sub-bandgap Excitation in Methylammonium Lead Iodide Thin Films: Effects of Urbach Tail, Deep Defects, and Two-Photon Absorption

Cited by 52 publications

References 39 publications

Quantum Dot Passivation of Halide Perovskite Films with Reduced Defects, Suppressed Phase Segregation, and Enhanced Stability

Quantum Dot Passivation of Halide Perovskite Films with Reduced Defects, Suppressed Phase Segregation, and Enhanced Stability

How Deep Hole Traps Affect the Charge Dynamics and Collection in Bare and Bilayers of Methylammonium Lead Bromide

Effect of PbSO4-Oleate Coverage on Cesium Lead Halide Perovskite Quantum Dots to Control Halide Exchange Kinetics

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