Vacuum-Induced Degradation of 2D Perovskites

Abstract

Two-dimensional (2D) hybrid organic-inorganic perovskites have recently attracted the attention of the scientific community due to their exciting optical and electronic properties as well as enhanced stability upon exposure to environmental factors. In this work, we investigate 2D perovskite layers with a range of organic cations and report on the Achilles heel of these materials-their significant degradation upon exposure to vacuum. We demonstrate that vacuum exposure induces the formation of a metallic lead species, accompanied by a loss of the organic cation from the perovskite. We investigate the dynamics of this reaction, as well as the influence of other factors, such as X-ray irradiation. Furthermore, we characterize the effect of degradation on the microstructure of the 2D layers. Our study highlights that despite earlier reports, 2D perovskites may exhibit instabilities, the chemistry of which should be identified and investigated in order to develop suitable mitigation strategies.

The Future of Perovskite Photovoltaics—Thermal Evaporation or Solution Processing?

“…Many reports demonstrate the detrimental role of grain boundaries in affecting the stability of perovskite layers, [57,58] suggesting that the typically observed very small grains of thermally evaporated perovskites can be a significant disadvantage for device stability. Moreover, exposure to vacuum has been shown to lead to the degradation of both 3D and 2D perovskites, [133,134] raising questions regarding the potential influence of exposure to vacuum during the deposition of thermally evaporated perovskites. Significantly more research is required to assess the stability of films and devices fabricated by the different deposition methods and develop appropriate strategies for its mitigation, which might differ depending on how the film was deposited.…”

23.7% Efficient inverted perovskite solar cells by dual interfacial modification

“…Despite this class of cations being commonly used for the formation of low-dimensional perovskites (23)(24)(25)(26), in our work, we adopt a different strategy and use a very low concentration to modify both interfaces of inverted perovskite solar cells. We find that this approach does not change the bulk perovskite crystal structure or its dimensionality but rather improves the interfaces by facilitating high-quality film formation on top of the HTL and inducing efficient defect passivation at the perovskite/ETL interface.…”

Organoammonium-Ion-based Perovskites Can Degrade to Pb0 via Amine–Pb(II) Coordination

“…Organic-based lead halide perovskites have been broadly investigated , for photovoltaics, light-emitting diodes, , and lasers and as substrates for fundamental studies of optical and electronic properties. − They display defect tolerance, band-gap tunability, and practicable solution processing, but their long-term stability can be problematic and is clearly a prerequisite for practical device utilization. In particular, forming Pb 0 can be deleterious during fabrication or under operating conditions. − Sterically small alkylammonium cations (such as methylammonium) are commonly found in crystalline “3D” bulk perovskites; larger ones with broader structural variation are used as spacers in “2D” layered or mixed “2 D /3D” species. ,− While it is commonly assumed that an ammonium lead iodide perovskite can degrade to an amine, HI and PbI 2 that subsequently yields I 2 and Pb 0 , ,, an under-appreciated pathway for formation of Pb 0 is based instead on the fundamental chemistry of Pb–N bonding: , Pb II and amine nitrogen are “soft” Lewis acids and bases, respectively, and Pb II -amine coordination is expected to be strong. Here we show that reduction of Pb II to Pb 0 can occur by a “redox” reaction in a Pb II -coordinated amine, both in the model system, PbI 2 , and in a family of 2D perovskites.…”