High Conductivity Copper Iodide $(\gamma-\text{CuI})$ Thin Films Deposited by a Spin-Coating Technique

The preparation of p+ hole transport layers (HTLs) with high transparency and conductivity is an important step for the development of thin film electronic devices such as solar cells, thin film transistors, and photodetectors; especially, when the films are prepared by low-cost techniques such as spin-coating from a solution. In this study, the deposition of CuI thin films with appropriate properties, using a spin-coating technique, is explained. Single and double layers were obtained (thicknesses up to 75 nm). The material was formed by nanocrystals (27 nm) with a single plane orientation along the diagonal of the zinc-blende cubic lattice (FCC). The bandgap in average was 2.98 eV, assuring high transparency in the visible range. The conductivity was in the range from 0.05 to 0.1 (S/cm), with hole concentrations in the range from 2 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{4} \times \mathbf{10}^{\mathbf{19}}\ \mathbf{cm}^{-\mathbf{3}}$</tex>, and mobilities around <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3}\ \mathbf{cm}^{\mathbf{2}}/\mathbf{Vs}$</tex>, which correspond to high values for this material when prepared by spin-coating, achieved previously only when doping it with iodide. In addition, the morphological (coverage and uniformity) characteristics for the double layers are much better than those reported by other researchers.