Transparent Electrodes for Efficient Optoelectronics

Abstract

With the development of new generations of optoelectronic devices that combine high performance and novel functionalities (e.g., flexibility/bendability, adaptability, semi or full transparency), several classes of transparent electrodes have been developed in recent years. These range from optimized transparent conductive oxides (TCOs), which are historically the most commonly used transparent electrodes, to new electrodes made from nano‐ and 2D materials (e.g., metal nanowire networks and graphene), and to hybrid electrodes that integrate TCOs or dielectrics with nanowires, metal grids, or ultrathin metal films. Here, the most relevant transparent electrodes developed to date are introduced, their fundamental properties are described, and their materials are classified according to specific application requirements in high efficiency solar cells and flexible organic light‐emitting diodes (OLEDs). This information serves as a guideline for selecting and developing appropriate transparent electrodes according to intended application requirements and functionality.

Graphene‐Based Transparent Conductive Films: Material Systems, Preparation and Applications

“…Metals such as silver and copper are highly conductive materials, which are not transparent under normal state. Nevertheless, their conductivity and transmittance can be tuned by dimensional engineering . The modulated arrangement can enable the system to conduct in one direction and be transparent in the order, which has been achieved by patterning the metal nanomaterials with formation of NWs, very thin layers, uniform metallic grids or meshes.…”

“…Graphene is a highly recommended material for TCFs due to its excellent electrical conductivity and optical transmittance in the visible and near‐infrared (NIR) region . Moreover, graphene exhibits high flexibility and outstanding chemical stability .…”

In2O3‐Based Transparent Conducting Oxide Films with High Electron Mobility Fabricated at Low Process Temperatures

“…The continuous development of solar cells (e.g., thin‐film Si, chalcopyrite, organic, perovskite, and Si‐wafer‐based heterojunction solar cells) has stimulated research on TCO films (e.g., In 2 O 3 , ZnO, and SnO 2 ). For example, high electron mobility is required for the TCO films used in solar cells because a high‐mobility results in a low sheet resistance at a low carrier density, providing high transparency with reduced free‐carrier absorption in the visible and near‐infrared regions . Low‐temperature growth is also required because of the presence of temperature‐sensitive layers in many solar cells (e.g., Si heterojunction, Cu(In,Ga)(Se,S) 2 , and perovskite solar cells).…”

Toward Annealing‐Stable Molybdenum‐Oxide‐Based Hole‐Selective Contacts For Silicon Photovoltaics

“…To ensure passivation of the silicon surface, an additional a‐Si:H buffer layer was inserted underneath this MoO X film, similar as in conventional SHJ technology. The MoO X film was capped with a transparent conductive oxide (TCO), either a stack consisting of hydrogen doped indium oxide (IO:H) and indium tinoxide (ITO) or simply ITO, to minimize resistive losses and maximize light in‐coupling . To finish the devices, a Cu front grid electrode was formed by electroplating.…”