**2. Thin film based supercapacitors**

Recently electronic devices such as computers, roll-up displays smartwatches, mobile phones and other portable devices abound in the twenty-first century. For greater performance, improved energy storage devices are required to reduce the energy consumption of these smart electronic devices [33]. As a result, devices with long-lasting battery, high power outputs, and quick recharge times are required. As a consequence, it is critical to create innovative energy storage materials and devices. The realities of scarcity of fossil fuels, and environmental damage should all be considered in this endeavor [34]. By modify the surface properties of the electrodes with a long life cycle, the supercapacitor (SC) is such an effective energy-saving technology that is environmentally friendly with quick charging, and high energy density are just a few of the benefits [35]. However, this redeemer (supercapacitor) has issues. Nevertheless, in comparison to lithium batteries, such savior (supercapacitor) has challenges such as poorer energy density, unavailability, and the high cost of ruthenium (IV) oxide (RuO2) and platinum electrode materials, all of whom have stymied the supercapacitor development. Supercapacitors, which are versatile, compact, ecologically benign, and yet still economical energy storage devices, are in growing market. The flexible supercapacitors, which bridges the gap between batteries and traditional capacitors, is a bright spot in the realm of energy-saving engineering. Flexible-all-solid-state thin film supercapacitor, an innovative novel thing, has gotten a lot of interest as unique energy storage devices because of its friendly construction, compact size, easy handling, and excellent power density with a quick chargingdischarging rate. The supercapacitor is called as electrochemical capacitors it has a fast charging and discharging properties, excellent power density and high specific capacitance with compact construction, and inexpensive cost of maintenance. The three primary mechanisms of supercapacitor can be classified (**Figure 1**), which is

*Recent Developments on the Properties of Chalcogenide Thin Films DOI: http://dx.doi.org/10.5772/intechopen.102429*

depending of the reversible redox reactions and the accumulation of charge. There is electric double layer capacitors (EDLC), pseudo capacitor, and the combination of EDLC and pseudo capacitor called the hybrid supercapacitor [36].

Thin films are very intriguing in modern research for a variety of applications in ethanol sensor, photocatalytic, thermoelectric and supercapacitor [37–40]. The supercapacitors can store the electrical energy for all the electronic devices to stabilize the power supply. Generally, to prepare a pseudo capacitive electrode transition metal oxide (TMO) is the most popular approach, however relatively higher electrical resistivity restricts whose use several fields. As a consequence, the focus of researchers is turning to metal chalcogenides, which have a lower electrical resistivity than oxygen due to sulfur's low electronegativity. The preponderance of these metal chalcogenides, mostly sulfides, are made from inexpensive and abundant transition metals. For example, Dai and co-workers [41] have prepared hierarchically structured Ni3S2 and multi-walled carbon nanotube (MWCNT) composites using the hydrothermal methods and the prepared device can have obtained the maximum Cs of 55.8 F g−1, it provides a highest energy density of 19.8 Wh/kg at power density of 789 W/kg. Xiao and co-workers [42] prepared a nickel cobalt sulfide nanoparticle graphene-based sheet (NiCo2S4@GR) there is no surfactant through simple one-step solvo thermal method, which results revealed the maximum Cs of 1708 F g−1 at a current density of 1.0 A g−1, while comparing without graphene. Mukkabla and co-workers [43] reported a Poly(3,4-ethylenedioxypyrrole) (PEDOP) Enwrapped bismuth sulfide (Bi2S3) nano flowers hybrid flexible SCS, and composite offered a maximum Cs of 329 F g−1 at 0.4 A g−1. Furthermore, these are usually undergoing redox reactions between the metallic ions valence states. Besides, TMO and transition metal chalcogenides, various metal nitrides have previously been observed has outstanding results as electrodes in supercapacitors and lithium ion batteries with impressive results. Recently, metal nitrates also have superior abilities in electrochemical properties with excellent chemical stability. Metal nitrides have gotten a lot of interest as supercapacitors electrodes since they

have a lot of benefits. Metal nitrates have three major advantages. (1) It has a high σ (electrical conductivity) of 55,500 S/cm−1 while compared to the metal oxides as a result shows the excellent power density, (2) compared to the metal oxides and carbon based materials metal nitrates have a higher specific capacitance, which results shows the higher energy density, and (3) high mechanical stability. These characteristics make them extremely promising as high-performance supercapacitor electrodes. Balogun and co-workers [44] have summarized the performance of different metal nitrides like molybdenum nitrides (MoN), nickel nitride, titanium nitride. Among these metal nitrides, molybdenum nitride was considered as the first metal nitride which could be used as supercapacitor electrode materials. However, for supercapacitor applications, researchers mostly considering their materials cost and electrochemical performance. There are many transition metals and metal oxides are considerable for supercapacitor applications such as CuO, NiO, Mn3O4, Co3O4, Ni or CuCo2O4 and Ni or CuFe2O4 [45–50]. Compared to the other metal oxides, the metal ferrite based materials much attracted to the researchers. For example, Fe, Ni or Cu based Fe2O4 materials have an excellent performance in the energy storage applications. There are two major methods could be used to prepare the thin films supercapacitors, namely physical technique (physical vapor deposition and sputtering) and chemical method. The successive ionic layer adsorption and reaction (SILAR), spin coater, and chemical bath deposition (CBD) are some examples for chemical deposition method (**Figure 2**).

Bandgar and co-workers [51] studied the nature of starting materials on the properties of NiFe2O4 thin films for flexible supercapacitors. There are several morphologies could be observed (nanosheet, flower, and feather) through different salts such as nickel(II) chloride hexahydrate (NiCl2·6H2O), nickel nitrate [Ni(NO3)2·6H2O], and nickel sulfate hexahydrate (NiSO4·6H2O), respectively. The nanosheet based electrode material received the maximum Cs of 1139 Fg−1, nanoflower and feather achieved the good Cs of 677 and 435 F g−1, respectively. Immanuel and co-workers [52] have

**Figure 2.** *Thin films deposition techniques.*

*Recent Developments on the Properties of Chalcogenide Thin Films DOI: http://dx.doi.org/10.5772/intechopen.102429*

optimized the Cr doped Mn3O4 thin films for high performance supercapacitors using the SILAR method. The experimental results showed that 3 wt % of Cr doped Mn3O4 thin films exhibited the maximum Cs of 181 Fg−1 at the current density of 1 Ag−1.

Jesuraj and co-workers [53] studied the pristine and Li doped NiO thin films using the spin coating method. Kin and co-workers [54] prepared the carbon based flexible supercapacitors using the chemical vapor deposition. Yu and co-workers [55] have prepared the cobalt nickel oxide and sulfide heterostructure thin films through electrodeposition method for supercapacitor applications. The obtained findings revealed the maximum energy density of 78.2 Wh·kg−1 at 542.8 W·kg−1 and the high power density of 5440.2 W·kg−1. Recently, Immanuel and co-workers [56] synthesized Mn3O4 nanorod thin films via SILAR method. The prepared Mn3O4 thin films showed the maximum Cs value of 295 Fg−1 at the scan rate of 2 mVs−1. Vivek and co-workers [57] prepared a reliable electrode material, and results obtained a maximum Cs of 426.40 Fg−1 at a current density of 1 Ag−1. Arulraj and co-workers [58] prepared the cubic shaped Ag2S using the CBD method on Ni mesh. The prepared Ag2S used a working electrode, which electrochemical performance showed the highest Cs of 179 C/g at constant charge and discharge current density of 1 A/g.
