In situ investigation of the formation and metastability of formamidinium lead tri-iodide perovskite solar cells

Aguiar, J. Albino; Wozny, Sarah; Holesinger, T. G.; Aoki, Toshihiro; Patel, Maulik; Yang, Mengjin; Berry, Joseph J.; Al‐Jassim, Mowafak; Zhou, Weilie; Zhu, Kai

doi:10.1039/c6ee01079b

Cited by 89 publications

(71 citation statements)

References 48 publications

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“…To understand the role of DRCN5T in perovskite formation and crystal growth, X‐ray diffraction (XRD) patterns of the control film and the 7.5 Vol.% film were monitored upon different annealing temperatures: room temperature (RT), 50, 70, and 100 °C. A set of strong peaks at 14.1°, 28.5°, and 31.84° could be assigned to (110), (220), and (310) lattice planes of the standard crystal structure, indicating an orthorhombic crystal structure of halide perovskite with good crystallinity . Interestingly, the diffraction peak of the δ‐FAPbI 3 can be clearly observed at 11.7° for control film, but this δ‐phase is effectively suppressed in the 7.5 Vol.% film by the DRCN5T incorporation.…”

Section: Resultsmentioning

confidence: 93%

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

et al. 2019

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The additive engineering to hybrid organic‐inorganic perovskite precursors is an effective technique toward highly efficient stable photovoltaic devices, however, there is still a deficiency in fundamental understanding on how these additives affect the perovskite film and device performance as well. Herein is introduced a small organic molecule, DRCN5T, into a double‐cation perovskite precursor and the function on device performance is systematically investigated. An appropriate amount of DRCN5T into the precursor can promote the crystallization of film with successful suppression of δ‐FAPbI3 phase, reduce grain boundaries and adequately passivate the native defect sites. In addition, the incorporation of DRCN5T also regulates the energy level alignment of the perovskite to charge transport layer suitably. This leads to the promotion of charge transport, reduction in non‐radiative recombination, and boosts the efficiency to a value of 20.60% with greatly reduced hysteresis in the device. Moreover, the treatment by DRCN5T also significantly increases the stability of the devices in ambient environment. These findings open the gate to produce highly crystallized perovskite/organic‐molecule active layers toward commercialization of perovskite solar cells.

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Section: Resultsmentioning

confidence: 93%

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

et al. 2019

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“…16 In addition, combined scanning TEM and energy loss spectroscopy detected the presence of OH − ions at the FAPI grain boundaries, a sign of reacted water. 15 With these premises, the above observations 1) − 4) become clear. The superior stability, even in humid air, of α−FAPI in loose powder with respect to the compacted form is explained with the fact that the powder has few grain boundaries, if any, whereas in the compacted powder, as in films, each grain is circumscribed by grain boundaries acting as water condensation centers.…”

Section: Introductionmentioning

confidence: 80%

Stability of Cubic FAPbI₃ from X-ray Diffraction, Anelastic, and Dielectric Measurements

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Craciun

Trequattrini

et al. 2019

J. Phys. Chem. Lett.

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Among the hybrid metal-organic perovskites for photovoltaic applications FAPbI 3 (FAPI) has the best performance regarding efficiency and the worst regarding stability, even though the reports on its stability are highly contradictory. In particular, since at room temperature the cubic α phase, black and with high photovoltaic efficiency, is metastable against the yellow hexagonal δ phase, it is believed that α−FAPI spontaneously transform into δ−FAPI within a relatively short time. We performed X-ray diffraction and thermogravimetric measurements on loose powder of FAPI, and present the first complete dielectric and anelastic spectra of compacted FAPI samples under various conditions. We found that α−FAPI is perfectly stable for at least 100 days, the duration of the experiments, unless extrinsic factors induce its degradation. In our tests, degradation was detected after exposure to humidity, strongly accelerated by grain boundaries and the presence of δ phase, but it was not noticeable on the loose powder kept in air under normal laboratory illumination. These findings have strong implications on the strategies for improving the stability of FAPI without diminishing its photovoltaic efficiency through modifications of its composition. Graphical TOC Entry1 arXiv:1905.02992v1 [cond-mat.mtrl-sci] 8 May 2019Although MAPbI 3 (MAPI, MA = methylammonium CH 3 NH 3 ) is the most studied hybrid metal-organic perovskite for photovoltaic applications, 1 better performance in terms of photovoltaic efficiency are found in FAPbI 3 (FAPI, FA = formamidinium CH(NH 2 ) 2 ). This is due both to a smaller bandgap of FAPI and to the fact that the FA + ion, in spite of a smaller electric dipole with respect to MA + , has a much larger quadrupole and faster reorientation dynamics that better screen the photoexcited carriers, enhancing their lifetime. 2 FAPI also has a better stability than MAPI at high temperature but its major flaw is that the black cubic α phase, which has the high photovoltaic efficiency, is metastable at room temperature, where instead the stable phase, and the one obtained by standard chemical methods, is the yellow hexagonal δ phase. For these reasons, major efforts are directed now at trying to stabilize the cubic α phase of FAPI through partial substitutions of FA with MA, Cs, etc. or I with Br, although this approach increases the bandgap. 3,4 It has been discussed, based on neutron diffraction measurements and simulations, that the α → δ transformation is complex and occurs through various intermediate stages, requiring to overcome a free energy barrier estimated in the order of hundreds of milli-electron volt. 5 This explains why the α phase of FAPI is kinetically trapped, resulting in a large thermal hysteresis between the δ → α transition at T h δα = 350 K and the α → δ at T c δα = 290 K. 5 Actually, the barrier for the α → δ transition has not been measured, and there is complete uncertainty on the kinetics of this transition. Indeed, also the reported temperatures for the δ → α transition during heati...

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“…In situ X-ray diffraction (XRD) offers such insights, as evidenced by studies2122232425 performed on methylammonium-based perovskites. However, to the best of our knowledge, there is only one publication on in situ diffraction of FAPbI 3 based perovskites by Aguiar et al 26. where they found 175 °C as the optimum processing temperature for FAPbI 3 .…”

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confidence: 99%

Thermal engineering of FAPbI3 perovskite material via radiative thermal annealing and in situ XRD

et al. 2017

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Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space of FAPbI3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI3 annealing time, 10 min at 170 °C, can be significantly reduced to 40 s at 170 °C without affecting the photovoltaic performance. The Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI3 into PbI2.

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In situ investigation of the formation and metastability of formamidinium lead tri-iodide perovskite solar cells

Abstract: Organic–inorganic perovskites have emerged as an important class of next generation solar cells due to their remarkable low cost, band gap, and sub-900 nm absorption onset.

Cited by 89 publications

References 48 publications

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

Stability of Cubic FAPbI₃ from X-ray Diffraction, Anelastic, and Dielectric Measurements

Thermal engineering of FAPbI3 perovskite material via radiative thermal annealing and in situ XRD

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In situ investigation of the formation and metastability of formamidinium lead tri-iodide perovskite solar cells

Abstract: Organic–inorganic perovskites have emerged as an important class of next generation solar cells due to their remarkable low cost, band gap, and sub-900 nm absorption onset.

Cited by 89 publications

References 48 publications

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

The Positive Function of Incorporation of Small Molecules into Perovskite Materials for High‐Efficient Stable Solar Cells

Stability of Cubic FAPbI3 from X-ray Diffraction, Anelastic, and Dielectric Measurements

Thermal engineering of FAPbI3 perovskite material via radiative thermal annealing and in situ XRD

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Stability of Cubic FAPbI₃ from X-ray Diffraction, Anelastic, and Dielectric Measurements