Table 12.

Challenges and their possible solutions associated with thin films are addressed by different authors.

Authors	Challenges Addressed		Possible Solutions
	Issues	Abbreviation
Naghdi et al. [30]	Sintering process and substrate compatibility	The selection of substrates is limited by the sintering process’s temperature requirements, which are necessary to enhance the conductivity of thin coatings. Although raising the sintering temperature can improve conductivity, it also increases the risk of pore formation and reduced functionality. To increase the variety of substrates, the sintering temperature must be lowered.	Reducing the size of nanomaterials can increase film conductivity, increase substrate possibilities, and decrease the sintering temperature.
	Problem associated with film thickness	A thicker film has better electrical conductivity but less optical transparency. The ideal thickness must be determined to balance these opposing qualities.	Determining the ideal thin-film thickness that balances optical transparency and electrical conductivity should be maintained.
	Aspect ratio	Increasing the aspect ratio lowers the percolation threshold, which is essential for cutting production costs without sacrificing mechanical qualities.	Conductive metal nanoparticles can be incorporated into polymers or mixed with other nanomaterials to generate hybrid materials with improved mechanical properties, conductivity, and customized functionality.
	Adhesion problem	Poor adhesion between the substrate and the thin film during deposition can cause problems when the film is stretched or bent, jeopardizing its integrity and performance.	By employing polydopamine, the substrate’s wettability can be changed. The hydrophilic condition of the substrate surface facilitates the deposition of Ag NWs, which improves the adhesion between the thin film and the elastomeric substrate. This method may create a transparent Ag NW thin film with improved adhesion, excellent optical transparency, minimal sheet resistance, and stability, even after the sample has been stretched.
Litzelman et al. [545]	Variations in the properties	The characteristics of nanostructured electrode and electrolyte components produced using thin-film fabrication techniques can differ greatly from those of bulk materials.	Minimizing differences in characteristics from bulk materials by improving thin-film fabrication methods.
	Variations in ionic conductivity	The performance of SOFCs can be affected by changes in ionic conductivity caused by internal interfaces within the nanostructured components.	Designing interfaces to improve ionic conductivity or reduce adverse effects, maybe by changing the materials’ surface or chemistry.
	Long-term stability	Increased cation diffusion along grain boundaries may affect the devices’ long-term stability. Enhancing membranes’ mechanical stability and thermomechanical dependability, especially when exposed to greater temperatures and for extended periods of time, is crucial.	Finding the sources of lingering tensions and the progression of stresses in the films is crucial to achieving this. Furthermore, using stress-tolerant designs is a possible remedy to alleviate these problems.
Zhang et al. [546]	Achieving high performance and stability at a low cost	The technical challenge is to minimize costs while maintaining high performance and stability. This requires creating large cells with low grain boundary resistance and thin, gas-tight electrolytes.	Using theoretical insights from density functional theory investigations, and machine learning can be used in material design to expedite the process and find useful characteristics for innovative materials.
Kalinina et al. [547]	Creating conductivity on non-conductive substrates	Conductivity must be established on the surface of non-conductive substrates in order to apply electrophoretic deposition (EPD).	Developing methods for the successful deposition of the Ce0.8Sm0.2O1.9 (SDC) electrolyte film, such as the formation of conductive sublayers such as PPy and Pt on the front surface of the non-conductive substrate.
	Mechanical stresses in the formation of bilayer films	The EPD of CuO-modified BaCe0.5Zr0.3Y0.1Yb0.1O3−δ (BCZYYbO-CuO/SDC) and SDC films on reduced Ni-SDC substrates results in significant mechanical strains that cause cracks in the bilayer film and disintegration of the single SDC film during the oxidative co-sintering process that follows.	Changing the anode substrate’s composition or altering the deposition process’s characteristics
Patil et al. [548]	Achieving high energy density and power density	A difficulty in developing lithium-based thin-film rechargeable batteries is achieving higher energy and power densities without sacrificing appropriate power densities.	By increasing the energy density of thin-film batteries, concentrating on technology development and improvements in the electrode process, within the next five to six years, it is possible to obtain energy densities exceeding 500 Wh/L and 200 Wh/kg by investigating novel active materials and electrode technologies.
Liu and Wöll [549]	Thin-film quality	For MOF thin films to find widespread use, their surfaces must be smooth, crystalline, aligned, compact, uniform, and free of pinholes, yet this is still a difficult task.	The film can be improved and oriented by employing techniques such as ALD and Liquid Phase Epitaxy (LPE).
	Defect control	Flaws must be controlled for MOF thin films to function as well as possible, yet characterizing and managing defects is difficult.	Advanced characterization methods, such as electron microscopy, spectroscopy, and synchrotron X-ray diffraction, can be utilized to study and manage flaws in MOF thin films. Techniques like “defective linkers” or controlled heating introduce defects in a controlled manner.
	Enhancing electrical conductivity	The intrinsic features of most <span id=“zotero-drag”/> MOFs make them poor electrical conductors, which restricts their use in energy storage systems.	Techniques include loading organic guest molecules into MOF voids, creating conductive polymers inside MOF frameworks, or creating MOFs with intrinsic conductive qualities by utilizing highly conjugated linkers, which can all be used to improve electrical conductivity.
Eslamian [550]	Development of Continuous and Integrated Thin Films	Spray coating presents a difficulty in producing thin layers that are consistent, high-quality, and integrated. The efficiency of current approaches is frequently lower than that of spin-coating, indicating a need for improved spray coating techniques.	Applying spray-coating-specific optimal processing conditions can improve the homogeneity and quality of thin films. Fine-tuning variables can enhance film morphology and device performance, including substrate temperature, nozzle distance, and spray rate.
	Effective Charge Separation, Transfer, and Collection	One of the largest challenges in spray-on layers is to ensure effective charge separation, transfer, and collection.	Using numerous spray passes increases the device’s overall efficiency by improving the coating’s thickness and coverage. Iterative deposition methods enable improved control over the film’s shape and characteristics.