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1.
J Phys Chem Lett ; 12(18): 4362-4367, 2021 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-33938752

RESUMO

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

2.
J Phys Chem Lett ; 11(16): 6772-6778, 2020 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-32689804

RESUMO

Hybrid perovskite solar cells attract a great deal of attention due to the feasibility of their low-cost production and their demonstration of impressive power conversion efficiencies (PCEs) exceeding 25%. However, the insufficient intrinsic stability of lead halides under light soaking and thermal stress impedes practical implementation of this technology. Herein, we show that the photothermal aging of a widely used perovskite light absorber such as MAPbI3 can be suppressed significantly by using polyvinylcarbazole (PVC) as a stabilizing agent. By applying a few complementary methods, we reveal that the PVC additive leads to passivation of defects in the absorber material. Introducing an optimal content of PVC into MAPbI3 delivers a PCE of 18.7% in combination with a significantly improved solar cell operational lifetime: devices retained ∼70% of the initial efficiency after light soaking for 1500 h, whereas the control samples without PVC degraded almost completely under the same conditions.

3.
ACS Appl Mater Interfaces ; 12(16): 19161-19173, 2020 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-32233360

RESUMO

We investigated the impact of a series of hole transport layer (HTL) materials such as Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), NiOx, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), and polytriarylamine (PTA) on photostability of thin films and solar cells based on MAPbI3, Cs0.15FA0.85PbI3, Cs0.1MA0.15FA0.75PbI3, Cs0.1MA0.15FA0.75Pb(Br0.15I0.85)3, and Cs0.15FA0.85Pb(Br0.15I0.85)3 complex lead halides. Mixed halide perovskites showed reduced photostability in comparison with similar iodide-only compositions. In particular, we observed light-induced recrystallization of all perovskite films except MAPbI3 with the strongest effects revealed for Br-containing systems. Moreover, halide and ß FAPbI3 phase segregations were also observed mostly in mixed-halide systems. Interestingly, coating perovskite films with the PCBM layer spectacularly suppressed light-induced growth of crystalline domains as well as segregation of Br-rich and I-rich phases or ß FAPbI3. We strongly believe that all three effects are promoted by the light-induced formation of surface defects, which are healed by adjacent PCBM coating. While comparing different hole-transport materials, we found that NiOx and PEDOT:PSS are the least suitable HTLs because of their interfacial (photo)chemical interactions with perovskite absorbers. On the contrary, polyarylamine-type HTLs PTA and PTAA form rather stable interfaces, which makes them the best candidates for durable p-i-n perovskite solar cells. Indeed, multilayered ITO/PTA(A)/MAPbI3/PCBM stacks revealed no aging effects within 1000 h of continuous light soaking and delivered stable and high power conversion efficiencies in solar cells. The obtained results suggest that using polyarylamine-type HTLs and simple single-phase perovskite compositions pave a way for designing stable and efficient perovskite solar cells.

4.
J Phys Chem A ; 124(1): 135-140, 2020 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-31820980

RESUMO

Thermal effects in organo-metal halide perovskites are studied by ab initio molecular dynamics (MD) simulations performed at effective temperatures of 293 and 383 K and by X-ray photoelectron spectroscopy (XPS). We find that the cause of thermal instability in this class of perovskites is the rotation of the methylammonium (MA) groups that destroy the rigid lattice of pure compounds (MAPbI3 and MAPbBr3). When the Pb-I lattice is initially distorted by partial replacement of the I with Cl or Br, this not only prevents formation of PbI2 seeds but also improves lattice flexibility and stability against the temperature-induced motion and rotation of MA groups.

5.
J Phys Chem Lett ; 11(1): 333-339, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31838849

RESUMO

We report the first systematic assessment of intrinsic photothermal stability of a large panel of complex lead halides APbX3 incorporating different univalent cations (A = CH3NH3+, [NH2CHNH2]+, Cs+) and halogen anions (X = Br, I) using a series of analytical techniques such as UV-vis and X-ray photoelectron spectroscopy, X-ray diffraction, EDX analysis, atomic force and scanning electron microscopy, ESR spectroscopy, and mass spectrometry. We show that heat stress and light soaking induce a severe degradation of perovskite films even in the absence of oxygen and moisture. The stability of complex lead halides increases in the order MAPbBr3 < MAPbI3 < FAPbI3 < FAPbBr3 < CsPbI3 < CsPbBr3, thus featuring all-inorganic perovskites as the most promising absorbers for stable perovskite solar cells. An important correlation was found between the stability of the complex lead halides and the volatility of univalent cation halides incorporated in their structure. The established relationship provides useful guidelines for designing new complex metal halides with immensely improved stability.

6.
J Phys Condens Matter ; 32(9): 095501, 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-31722319

RESUMO

In this study, we investigate the photo-/thermal degradation mechanism of hybrid perovskites by using x-ray photoelectron (XPS) valence band (VB) spectra coupling with density functional theory (DFT) calculations. Herein, CH3NH3PbI3 is respectively subjected to irradiation with visible light and annealing at an exposure of 0-1000 h. It is found from XPS survey spectra that, in both cases (irradiation and annealing), a decrease in the I:Pb ratio is observed with aging time, which unambiguously indicates the formation of PbI2 as the product of photo/thermal degradation. The comparison of the XPS VB spectra of irradiated and annealed perovskites with the DFT calculations of CH3NH3PbI3 and PbI2 compounds have showed a systematic decrease in the contribution of I-5p states, which allows us to determine the respective threshold for degradation, which is 500 h for light irradiation and 200 h for annealing. This discrepancy might be due to the fact that the relaxation of thermal excitations of the system is carried out only by the phonons (which are non-radiative physical processes) while the radiative processes occurred during the photoexcitation will elastically or inelastically divert part of the external energy from the system to reduce its impact on perovskite degradation.

7.
J Phys Chem Lett ; 10(4): 813-818, 2019 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-30621392

RESUMO

We report on the impact of γ radiation (0-500 Gy) on triple-cation Cs0.15MA0.10FA0.75Pb(Br0.17I0.83)3 perovskite solar cells. A set of experiments was designed to reveal the individual contributions of the hole-collecting bottom electrode, perovskite absorber, and electron transport layer (ETL) to the overall solar cell degradation under radiation exposure. We show that the glass/ITO/PEDOT:PSS hole-collecting electrode withstands a 500 Gy dose without any losses in the solar cell performance. In contrast, the perovskite absorber films and PC61BM ETL are very sensitive to γ rays, as can be concluded from the radiation-induced decay of the solar cell efficiency by ∼32-41%. Red shift of the perovskite emission bands and strong enhancement of the photoluminescence suggest that γ rays induce phase segregation of iodine-rich and bromine-rich domains, which represents the first reported example of the radiation-induced halide phase separation in perovskite films. The degradation pathway revealed here emphasizes the need for developing a new generation of metal halide absorbers and ETL materials with improved radiation stability to enable potential space applications of perovskite photovoltaics.

8.
ACS Appl Mater Interfaces ; 9(39): 33478-33483, 2017 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-28481102

RESUMO

We report reversible and irreversible strain effects and interfacial atomic mixing in MAPbI3/ITO under influence of external electric bias and photoillumination. Using conductive-probe atomic force microscopy, we locally applied a bias voltage between the MAPbI3/ITO and the conductive tip and observed local dynamic strain effects and current under conditions of forward bias. We found that the reversible part of the strain is associated with a current spike at the current onset stage and can therefore be related to an electrochemical process accompanied by local molar volume change. Similar partly reversible surface deformation was observed when the tip-sample contact was illuminated by light. Time-of-flight secondary ion mass spectrometry of electrically biased regions revealed massive atomic mixing at the buried MAPbI3/ITO interface, while the top MAPbI3 surface, subjected to strong morphological damage at the tip-surface contact, revealed less significant chemical decomposition.

9.
J Phys Chem Lett ; 8(6): 1211-1218, 2017 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-28220700

RESUMO

We report a careful and systematic study of thermal and photochemical degradation of a series of complex haloplumbates APbX3 (X = I, Br) with hybrid organic (A+ = CH3NH3) and inorganic (A+ = Cs+) cations under anoxic conditions (i.e., without exposure to oxygen and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI3) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the cesium-based all-inorganic complex lead halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks.

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