Concepts, fabrication and applications of MOF thin films in optoelectronics: A review

In the present review, various concepts and strategies for the fabrication of MOF thin film with various structures in optoelectronic applications are reviewed. The different nature of MOF thin film types leads to distinct promises and challenges for future applications. One of the strengths of thin film MOFs is the combination of molecular building blocks with the properties of a solid material. Some MOF films have intrinsic electrical conductivity. When used in thin films, these MOFs can perform charge transfer and injection within devices. Organic ligands and metal nodes in MOF thin films allow to adjust the bonding distance of the materials. This tunable property is valuable for adsorption and emission of MOF thin films in optoelectronic devices. However, the design and fabrication of composite MOF thin films present important challenges owing to limitations on the composition and the difficulty in maintaining the optoelectronic efficiency stably of thin films fabricated by general technique. MOF thin films and their properties can be used for possible usages in optical communication with linear and nonlinear optical mechanisms. However, the design and fabrication of composite MOF thin films present significant challenges due to restrictions on the composition and the difficulty in maintaining the optoelectronic performance stably of thin films fabricated by various techniques. When these MOFs are incorporated into thin films, they can enhance the absorption or emission of light, making them suitable for optoelectronic applications such as photodetectors, LEDs, sensors, batteries, supercapacitors and solar cells. There are various challenges to fabricate MOF thin films for optoelectronic application. Therefore, the property of the surface thin film must be changed during the coatings to lead to synergistic optical properties in the sample. Different approaches have been used to deposit MOF thin films for substrates, such as hydrothermal, solvothermal, layer by layer, electrochemical, spray, ultrasonic spray, spin coating, dip coating, vapor-assistant conversion, substrate-seeded heteroepitaxy, chemical vapor deposition, bottom-up modular assembly, and atomic layer deposition. Ligands with different functional topologies are statistically achievable in placing functional groups inside the MOF crystal. Thus, the structural design of thin film MOFs on different surfaces with changeable properties can be a future research focus for the development of optoelectronic devices. The review provides an insight into the fabrication strategies and their prospective optoelectronic applications.