Three-dimensional organic-inorganic hybrid halide perovskite materials have gathered a lot of interest due to their optoelectronic properties. However, in recent years, there has been a shift of focus building optoelectronic devices from 2D perovskite materials, but research has been hindered by the inability of researchers to pattern some of these perovskite materials as they become damaged by the solvents used in many top-down lithography methods.

Jr-Hau He, King Abdullah University of Science & Technology (KAUST), Saudi Arabia, and Xiaosheng Fang, Fudan University, China, and colleagues have modified the electron beam lithography (EBL) method by using an orthogonal processing approach. To do this, they used solvents, namely chlorobenzene and hexene, which are orthogonal to the perovskite materials.

This approach was found to be an effective method of producing a 2D layered perovskite single-crystal photodetector, with a structure of (C₆H₅C₂H₄NH₃)₂PbI₄, without affecting its optical or electronic properties. The two solvents were chosen because hexane has almost no polarity due to its symmetrical nature and lack of polar bonds, which was ideal for cleaning and processing the perovskite, whereas chlorobenzene has a very small polarity and could be used to etch the poly(methyl methacrylate) (PMMA) resists used in the lithographic process, without etching the perovskite itself. Thus, it allowed for an effective patterning of the surface.

In addition to the perovskite single crystal, the researchers also patterned nanoscale electrodes and the photodetector showed a photoresponsivity of 5.4 mA/W and a photodetectivity of 1.07·10¹³ Hz^1/2/W.

• Orthogonal Lithography for Halide Perovskite Optoelectronic Nanodevices,
  Chun-Ho Lin, Bin Cheng, Ting-You Li, José Ramón Durán Retamal, Tzu-Chiao Wei, Hui-Chun Fu, Xiaosheng Fang, Jr-Hau He,
  ACS Nano 2018.
  https://doi.org/10.1021/acsnano.8b05859