AVS 65th International Symposium & Exhibition
    2D Materials Focus Topic Tuesday Sessions
       Session 2D+EM+MI+NS-TuM

Paper 2D+EM+MI+NS-TuM2
Out-of-Plane Mechanical Properties of 2D Hybrid Organic-Inorganic Perovskites by Nanoindentation

Tuesday, October 23, 2018, 8:20 am, Room 201B

Session: Properties of 2D Materials including Electronic, Magnetic, Mechanical, Optical, and Thermal Properties
Presenter: Qing Tu, Northwestern University
Authors: Q. Tu, Northwestern University
I. Spanopoulos, Northwestern University
S. Hao, Northwestern University
C. Wolverton, Northwestern University
M. Kanatzidis, Northwestern University
G. Shekhawat, Northwestern University
V. Dravid, Northwestern University
Correspondent: Click to Email
2D layered hybrid organic-inorganic perovskites (HOIPs) have demonstrated improved stability and promising photovoltaic performance. The mechanical properties of such functional materials are both fundamentally and practically important to achieve both high performance and mechanically stable (flexible) devices. Here we report the static, out-of-plane mechanical properties of a series of 2D layered lead iodide HOIPs with a general formula of (R-NH3)2(CH3NH3)n-1PbnI3n+1, and investigate the role of structural sub-units (e.g., the length of theorganic spacer molecules -R and the number of inorganic layer -n) on the mechanical properties by nanoindentation. We find that the 2D HOIPs are softer than their 3D counterparts due to the replacement of the strong inorganic layer and ionic bonds by the soft organic layers and the weak Van der Waals interactions. As n increases from 1 to 5, the relative amount of these weak factors in the crystals are decreasing and both the out-of-plane Young’s modulus E and hardness H increase, approaching to the reported values of corresponding 3D crystals. DFT simulations showed a similar trend to the experimental results. Furthermore, we show that increasing the alkyl chain spacer molecule -R from -C4H9 to -C12H25, E first decreases and eventually plateaus while no clear trend in H is observed. Our results reveal that the competition between the stiff inorganic layers, the soft organic layer and the weak Van der Waals interfaces determines the mechanical properties of 2D HOIPs. Finally, we compare these findings with those in other 2D layered materials such as h-BN, MoS2 and MXene, and shed light on routes to further tune the out-of-plane mechanical properties of 2D layered HOIPs.