Abstract
Organic–inorganic halide perovskites (OIHPs) have the typical composition of APbX3, in which A is a cation such as methlyamine (MA) and formamidine (FA) and X is a halide anion such as Cl, Br, or I. The mixture at the A or X site in OIHPs provides greatly improved versatility in their compositions and therefore allows the enhancement of their performance in LEDs and solar cells. In real application circumstances and deformable devices, the mechanical properties of OIHPs are of great importance. In this work, the mechanical properties of three series of mixed OIHP single crystals, MAPbIxBr3−x, MAPbBrxCl3−x, and FAyMA1−yPbBr3, are studied by nanoindentation. The results are summarized according to the composition of these mixtures. With the increase in the FA content at the A site, the average Young’s modulus (E) of FAyMA1−yPbBr3 decreases greatly from 19.2 GPa to 11.5 GPa, which indicates that the influence of organic cations on the mechanical properties of OIHPs is as important as that of Pb-X bonds. The mixture at the A or X site could also increase the hardness (H) and the wear resistance (H/E ratio). The average values of hardness and wear resistance of MAPbI0.1Br2.9 are almost double (0.63 GPa, 0.033) the values for undoped MAPbBr3 (0.32 GPa, 0.017). The dynamic mechanical responses of the OIHP single crystals show reduced creep stress exponents and thus increased strain rate sensitivities in the mixture at the X site, thereby improving the ductility. The nanoindentation sites are characterized using a scanning electron microscope and slip bands are observed, suggesting the plastic deformation mechanism governed by the activation of dislocations.
Highlights
Organic–inorganic halide perovskites (OIHPs) provide an enhanced power-conversion efficiency in solar cells, currently reaching 25.2%.1 The OIHPs have exhibited excellent performances in light-emitting diodes,2 lasers,3 and photodetectors.4–7 The typical compositions of OIHPs can be expressed as ABX3, where A = CH3NH3+ (MA+), CH(NH2)2+ (FA+), or Cs+, B = Pb2+ or Sn2+, and X = I−, Br−, or Cl−
A series of MAPbIxBr3−x (x = 0–3), MAPbBrxCl3−x (x = 0–3), and FAyMA1−yPbBr3 (y = 0–1) single crystals are measured by nanoindentation
The values of x and y are evaluated by x-ray fluorescence (XRF) and nuclear magnetic resonance (NMR), respectively
Summary
Organic–inorganic halide perovskites (OIHPs) provide an enhanced power-conversion efficiency in solar cells, currently reaching 25.2%.1. Compared with the traditional inorganic energy materials, the OIHPs are even more suitable for wearable functional devices with high mechanical flexibility and robustness.. With the development of wearable electronics and perovskite photovoltaic devices, flexible perovskite solar cells have become candidates for mobile power supply to drive the generation of electronic products.. Almost all perovskite solar cell records are achieved with mixed A and/or X site hybrid OIHPs, which have promoted a better long-term stability in an ambient atmosphere, a higher hole mobility, and a longer carrier lifetime.. In order to apply the A-site or X-site mixed OIHPs on real devices and flexible devices, it is necessary to explore in depth their mechanical behaviors. The discrepancy of Young’s modulus (E) between the substrate and the functional thin films could scitation.org/journal/apm cause severe strain concentration and decrease the flexibility of electronic devices.
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