Organic-inorganic hybrid perovskites (OIHPs) have great potential for various applications like solar cells, lighting-emitting diodes (LEDs), field effect transistors (FETs) and photodetectors. Among their most important parameters influencing the power conversion efficiency (PCE) of devices based on perovskite materials is their carrier mobility. However, despite massive progress made by introducing new components into the structure to control the mobility of the carriers, the understanding on the atom level of how the components affect the performance is still lacking.

To address this problem, a research team led by Prof. Luo Yi and Prof. Ye Shuji from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) has synthesized a series of 2D OHIPs films with large organic spacer cations.

By a sequence of measurements, including sum frequency generation vibrational spectroscopy (SFG-VS), optical-pump terahertz-probe spectroscopy (OPTPS), current voltage (I-V) measurements, temperature-dependent PL spectroscopy and X-ray diffraction (XRD) measurements, the researchers found the correlation among the conformation of the organic cations, the charge-carrier mobility and broadband emission.

Mobility and broadband emission showed strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in 2D OIHP films. The interlayer distance and the conformational order of the organic cations co-regulate the out-of-plane mobility.

This work provides a physical understanding of the important role of organic cation conformation in optimizing the optoelectronic properties of 2D OIHPs, revealing the structure-property relationship in the perovskite research at the molecular level.

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