Transparent conductors are essential elements in an array of optoelectronic devices. The most commonly used transparent conductor – indium tin oxide (ITO) suffers from issues including poor mechanical flexibility, rising cost, and the need for annealing to achieve high conductivity. Consequently, there has been intensive research effort in developing ITO‐free transparent conductors over the recent years. This article gives a comprehensive review on the development of an important ITO‐free transparent conductor, that is based on thin metal films. It starts with the background knowledge of material selection for thin‐metal‐film‐based transparent conductors and then surveys various techniques to fabricate high‐quality thin metal films. Then, it introduces the spectroscopic ellipsometry method for characterizing thin metal films with high accuracy, and discusses the optical design procedure for optimizing transmittance through thin‐metal‐film‐based conductors. The review also summarizes diverse applications of thin‐metal‐film‐based transparent conductors, ranging from solar cells and organic light emitting diodes, to optical spectrum filters, low‐emissivity windows, and transparent electromagnetic interference coatings.

Figure 3. Three typical device architectures of "Sandwich", "Cross-array", and "Planar" structures. "Sandwich structure" Reproduced with permission. [13] Copyright 2015, Wiley-VCH. "Cross-array structure" Reproduced with permission. [21] Copyright 2019, Wiley-VCH. "Planar structure" Reproduced with permission. [16] Copyright 2020, Wiley-VCH.

In order to manufacture large-scale photonic devices of various dimensions at a low cost, a number of printing-based patterning techniques have been developed.