Table 8.

An overview of the impact of major factors on the transmittance of conductive thin films.

Thin Films	Factors	Effects on Transmittance	Authors
AZO	Doping	With increasing doping concentrations, the transmittance usually decreases.	Wang et al. [347], Alam and Cameron [214], Babu et al. [217]
		Higher doping levels (>2 at. %) may cause more photons to be scattered by doped crystal defects, causing a drop in transmittance Photons’ free carrier absorption causes a decrease in the optical transmission of strongly doped materials	Lee et al. [350]
		No matter the doping concentration, all films have high transparency in the visible (400–750 nm) optical spectrum, with values as high as 85% Bulk ZnO’s higher energy bandgap causes its transmittance to be higher in the visible spectrum	Peng et al. [382], Caglar et al. [215]
		The doped film containing 2 at. % Al has a transmittance over 90% higher than the doped film containing 3 and 4 at. %. This could be because there are more voids in the film with 2 at % than in the films with 3 and 4 at % doping. This resulted in an increase in transmittance and a decrease in optical scattering.	Babu et al. [217]
	Temperature	ZnO: Al films exhibit enhanced optical transmission in the visible spectrum upon annealing at elevated temperatures.	Alam and Cameron [214]
		Elevated substrate temperatures have the potential to enhance film adherence and impact the formation of crystalline formations, which in turn affects the optical qualities. During film growth or annealing, a significant temperature differential between the substrate and the surrounding air could introduce thermal stress. Thermal stress can affect the structural integrity of the film and, in turn, its optical performance.	Babu et al. [217]
		As substrate temperature increased, the average optical transmittance changed from 78% to 90%. The average grain size of the film may have increased, which could be the cause of the transmission increase. The increased homogeneity and crystallinity of AZO thin films can be credited with improving transmittance.	Barhoumi et al. [219]
		The visible transmittance (∼85%) stays almost constant as the annealing temperature rises from 500 to 650 ºC, while the infrared transmittance (from 780 to 2500 nm) significantly improves from 22% for the as-deposited film to 58% at 600 ºC and 71% at 650 °C for the annealed films. The films’ transmittance and crystallinity were enhanced by the high-temperature annealing	Gao et al. [348], Takci et al. [349]
	Thickness	Transmittance may decrease due to increased light absorption in the film caused by thickness.	Subba Reddy et al. [223], Lin et al. [346]
		The transmittance dropped to 50–70% from 70–90% when the deposited film thickness increased.	Hoon et al. [346]
		The films’ optical transmittance rose as the film thickness increased to 231 nm and dropped to a higher thickness of 398 nm.	Subba Reddy et al. [223]
	Surface morphology	The enhanced photon scattering caused by doping-induced crystal defects may cause the transmittance to drop at higher doping levels Film thickness can influence ZnO-thin-film surface morphology. Grain and roughness patterns on the surface may be more noticeable in thicker coatings.	Babu et al. [217]
	Coating	The transmittance is independent of the type or process of coating. The quantity of coatings had no appreciable impact on transmittances or bandgaps	Silva and Darbello Zaniquelli [212]
	Tilted angle	Despite the distorted structure, an average transmittance of >90% was achieved, demonstrating the generally high transparency of AZO film on a glass substrate.	Leem and Yu [220]
ITO	Film thickness	As ITO thin-film thickness increases, its transmittance decreases. The influence of grain size may be connected to this phenomenon. Light scattering results from an increase in grain size brought on by a thin film’s thickness. This phenomenon also could be attributed to free carrier absorption, which raises the concentration of carriers in thick films and enhances light absorption.	Eshaghi and Graeli [278]
		The measurements reveal strong transmittance throughout the visible spectrum with decreasing thickness. The transmittance decreases because of the high carrier concentration at higher wavelengths.	Maniscalco et al. [351]
	Changing compositions	When Sn doping concentration rises, optical tests indicate a modest decrease in transmittance. In the visible spectrum, the films’ transmittance showed a noticeable rise. The transmission peaked for undoped In2O3 and declined as the quantity of Sn increased. The reduction in light transmission was linked to (i) scattering at grain boundaries and (ii) oxygen vacancies. Since every film was deposited in an oxygen-rich environment and under identical processing circumstances, it was anticipated to experience the same transmission loss from oxygen flaws.	Senthilkumar et al. [202]
	Grain size	With the increasing concentration of Sn, the grain size decreased, resulting in a decrease in the transmittance. More grain boundaries and increased Sn dopant content increased scattering centers, leading to a reduction in transmission.	Senthilkumar et al. [202], Ogihara et al. [353], Katsube et al. [354]
	Deposition power and time	With the increment of the deposition time or power, a decrease in the average transmission is observed. The film thickness’s increment causes the transmission decrement The average transmittance fluctuates between 70% and 95% and decreases with increasing RF strength and deposition time.	Tchenka et al. [325]
CuI	Deposition technique	Thermal evaporation increases transmission by 70% in the 550–1000 nm wavelength range compared to other techniques. PLD technique provides the highest amount of transmittance	Kaushik et al. [56], Potts et al. [356], Burns et al. [357]
	Temperature	With the increasing substrate temperature, the transmittance increased. CuI thin-film structure and characteristics deteriorate with rising substrate temperature, as demonstrated by phase structure breaking and average transmittance falling.	Zi et al. [359], Zhu and Zhao [190]
		The transmittance decreased with the increasing annealing temperature. With an average transmittance of roughly 70–80%, all films are extremely transparent in the visible spectrum.	Moditswe et al. [54]
	Doping concentration	I2 doping of 1–5% shows high transparency in the visible range of the optical spectrum. The enhanced photon scattering by doping-induced crystal defects may cause a transmittance drop of up to 3 at. %. Transmittance increased after 4 at. % I2 doping, parallel to the resistivity value	Amalina et al. [191], Muiva et al. [216]
Polymer	Wavelength	20% of the composites are the ideal concentration, resulting in films with good visual transparency in polymeric PMMA that are 0.1 mm thick.	Carboni et al. [361]
	Doping concentration	According to the UV–vis transmittance spectra of PVDF pure and PVDF-ZnO nanocomposites, the transmittance of ultraviolet light reduced as the ZnO content in the nanocomposite films increased. The increase in surface roughness is the cause of the observed lower transmittance.	Indolia and Gaur [362]
	Polymer type and molecular structure	Polyethylene has a linear molecular structure comprising repeated ethylene units (-CH2-CH2-), so light can travel through it without absorption or scattering, resulting in outstanding optical transmittance.	Lahlouh [364]
		PS is composed of an ethylene-linked chain of aromatic benzene rings. The stiff and planar structure of the benzene rings facilitates the efficient transmission of visible light through the polymer matrix. When compared to its lower-molecular-weight competitors, high-molecular-weight PS shows better optical transmittance. PS thin films with longer polymer chains are better suited for high-optical-clarity applications like transparent packaging and optical lenses because they are less flawed and show less light scattering.	Zhou and Burkhart [365], Zhao et al. [366]
		PMMA thin films have a homogeneous molecular structure and little chain branching or crosslinking; as a result, they offer optical clarity and high transmittance throughout the visible spectrum	Klinger et al. [367]
	Film thickness	Reduced transmittance is often the result of thicker polymer sheets’ tendency to absorb light and scatter photons. In the visible spectrum, thin polymer films (less than 100 nm) could transmit higher. Photons may interact with molecular bonds, functional groups, or contaminants in the polymer film during light transmission, resulting in photon absorption and decreased transmittance. The polymer molecules’ absorption of light energy reduces the intensity of transmitted light.	Good et al. [368], Tsilingiris [369]
		As the PET film thickness rises, the polymer material absorbs more incident light, lowering optical clarity and transmittance.	Zhang and Zhang [370]
INO	Temperature	In the visible spectrum, all films exhibited high transparency with different annealing temperatures. Transmittance values drop in the longer wavelength range as the sintering temperature increases. The sample’s fluctuating oxygen content could be the cause. Films sintered at 500 °C displayed a narrower transparent window than those sintered at 300 °C, which may have exceeded the device’s detection limit.	Solieman [372]
		This film has the maximum thickness value. Its high transmittance may be due to the smooth surface feature. The following elements generally cause a decrease in the film’s transmittance: (i) mixed phases, (ii) thickness growth, (iii) defects and oxygen vacancies, (iv) surface roughness, (v) porous nature of the films, (vi) grain boundary scattering, etc. When substrate temperature rises, oxygen desorption may occur, creating oxygen vacancies. Therefore, the film created at Ts = 573 K should have the lowest transmittance value and more oxygen vacancies. The transmittance of films created at 300 K, which was the lowest substrate temperature, is high, approximately 96%.	Beena et al. [342]
		As substrate temperature rises, the films’ transmittance also increases.	Gupta et al. [344]
		As the annealing temperature rises from 350 to 500 °C, there is a notable increase in average transmittance. Upon annealing, the crystallinity of thin films increases. Their crystallinity likely influences the transparency of the films’ light scattering. Better transparency results from decreased light scattering as the films’ crystallinity increases.	Senthilkumar et al. [345]
		Crystallization improves the electrical and transmittance qualities of thin films.	Han et al. [373]
	Doping concertation	The transmittance of undoped In2O3 was the lowest, and it rose as the V doping level increased. The oxygen lost during evaporation is the reason for the poor transmittance of the undoped In2O3. Following doping, the V-doped In2O3 films exhibit an increase in transmittance and a decrease in reflectance,	Alqahtani et al. [374]
CdO	Oxygen pressure	The films formed at lower oxygen pressures display poorer transmittance values. Oxygen deficits and the absence of stoichiometry in the film can cause an inadequate oxygen ambiance. A stoichiometric film devoid of oxygen deficits can be achieved at elevated ambient oxygen levels. However, the quality of the film may decrease if the background oxygen pressure rises over this threshold because of the increased collision between laser plume species and background oxygen atoms. While the films deposited at an oxygen pressure of 0.2 mbar exhibit lesser transmittance, the films formed at an oxygen atmosphere of 0.02 mbar show very high transmittance. The film deposited at 0.02 mbar demonstrated significantly higher transmittance than the other films, indicating its superior quality.	Beena et al. [342]
	Temperature	The transmittance of deposited and annealed films rises non-linearly with wavelength The transmittance of deposited films is higher than that of annealed films at the same wavelength.	Ullah et al. [333]
		When a film is annealed at a higher temperature, the absorption edge changes to higher wavelengths.	Santos-Cruz et al. [334]
	Doping concentration	With 10 wt. % Al doping, the transparency falls between 70 and 80 percent in the visible spectrum.	Saha et al. [377]
		The transparency for the pure CdO film is 88%, increasing to 90% for the CdO film doped with 1% Mn. Higher Mn doping concentrations (more than 1 at. %) decrease transparency; the film coated with 4 at. % Mn achieves the lowest value of 78%. As the Mn doping concentration rises, the transmission edge changes to the longer-wavelength side, indicating a decrease in the optical bandgap of the CdO: Mn films. The transparency of CdO: Mn films with 2–4 at. % Mn concentration decreased due to the addition of Mn to the CdO lattice and an increase in the concentration of free charge carriers.	Manjula et al. [378], de Biasi and Grillo [379]
		Adding Al dopant to CdO thin films improves transmittance. The transmittance of the undoped films is 62%, which increased to 77% with 4 wt. % Al doping.	Kumaravel et al. [335]
		The addition of Al to CdO enhances transmission. The transmittance of the doped film containing 1 at. % Al is close to 90%, which is higher than that of the doped film containing 5 at. %. 1 at % doped film has comparatively lower optical scattering than the 5 at % doped films.	Ziabari et al. [339]
		The CdO film’s transmittance increased to 0.5 wt. % of La doping, but it decreased at 0.75 and 1 wt. (%) of doping. Compared to undoped CdO films, La-doped CdO thin films have comparatively high transmittance, suggesting their optoelectronic applications	Velusamy et al. [340]
		The transparency increases significantly with CdO film coated with 2 at. % Mg. At wavelengths longer than 500 nm, the maximum transmittance of the CdO: Mg film coated with 8 at. % Mg is almost equivalent to 90%. The film coated with 2 at. % Mg doping may have a higher thickness, which could account for its low transparency. A higher crystallite size value for this film may cause the increased absorption by free carriers brought about by increased film thickness.	Usharani et al. [338]