However, in this work, as PEDOT:PSS does not follow the design condition of AR coating, materials with low and high refractive indices have been placed at different positions with an overall optical thickness of λ/4 or λ/2 to optimize the reflectance spectra for PEDOT:PSS/c-Si heterojunction solar cells. The anti-reflection coating C is applied to the surface of a substrate such as a glass with the outermost layer being adjacent the air medium A. The measured reflectance spectra of PEDOT:PSS and simulated reflectance spectra as a function of wavelength of the double ARC layers for PEDOT:PSS/c-Si solar cell are shown in figure 3(b). Multilayer antireflective coatings can reaches the lowest reflectivity at a center wavelength. The invention of claim 5 wherein the optical thickness, N. 15. In the last few decades, solar cells based on crystalline silicon (c-Si) have dominated the photovoltaic technology with the market share of over 90% of the global market although it requires a very high temperature of ~1400 °C for the fabrication . These variations are produced by changing the mixing ratio of ZrO2 and TiO2, and/or by the change of evaporating conditions, etc. The anti-reflection coating C comprises a four-layer structure consisting of a first layer I, a second layer, II, a third layer, III, and a fourth layer, IV, in sequence from the air side to the glass substrate side. A single quarter-wavelength coating of optimum index can eliminate reflection at one wavelength. 3b represent the spectral reflectance characteristics of embodiments 4-6. As is clear from FIG. Although, PEDOT:PSS having refractive index (RI) of ~1.6 reduces the reflectance of the silicon to about 20%, it is still high for reducing the optical loss in the PEDOT:PSS/c-Si heterojunction solar cell [10, 21]. Broadband multilayer anti-reflective coating for the visible region, 0.5% Reflection average in the visible region (450nm–650nm). Therefore, it can be concluded that PEDOT:PSS can act as a single ARC layer in addition to hole transport for PEDOT:PSS/c-Si heterojunction solar cells [10, 12, 21, 24, 33–35]. More of the reflected light is in the red and blue extremes of the visible spectrum. A multi-layered anti-reflection coating for use with a substrate to reduce reflectance comprising four layers of material, each layer respectively having an effective optical thickness, Nd, of a preselected design wavelength Î»o as follows: wherein the subnumber refers to the layer sequentially numbered from the layer farthest from the substrate, N, 19. A third layer III is made from a material with a medium index of refraction ranging from 1.56 to 1.80, such as A2 O3, CeF3, MgO, Y2 O3 and Gd2 O3, and is within a range of 0.50 Î»o to 0.75 Î»o in optical thickness. Then these substrates were immersed in HF (5%) solution for 2.5 min and then rinsed in DI water and then dried by N2 gas blower. Screened for originality? 2 is a vector diagram for use in determining the optimum layer thicknesses; FIGS. (a) The chemical structure of PEDOT:PSS, (b) The schematic diagram of the PEDOT:PSS/c-Si heterojunction solar cell and (c) The schematic energy diagram of the PEDOT:PSS/c-Si solar cell. A multi-layer anti-reflection coating is provided having four layers. Jaker Hossain1, Bipanko Kumar Mondal1, Shaikh Khaled Mostaque1, Sheikh Rashel Al Ahmed2 and Hajime Shirai3, Published 9 December 2019 • The invention of claim 5 wherein the third layer is selected from a group consisting of Al, 14. The most interesting feature of this ARCs layer design is that all of the ARC layers have small physical thicknesses. Different types of materials having low (L) or high (H) refractive indices are placed as Layer 1 or Layer 2 on the top of PEDOT:PSS for achieving lowest reflectance. The colors used are to distinguish the layers, but not otherwise significant. Authors also appreciate Mr Snehashish Roy Chowdhury, Department of Electrical and Electronic Engineering, University of Rajshahi, Rajshahi 6205, Bangladesh, for his help in MATLAB coding. The invention of claim 7 wherein the optical thickness, N, 9. The thicknesses of PEDOT:PSS and materials with RI of 2.10 for λ/2-wavelength DARCs design are same 80 and 80 nm, respectively. Revised 23 October 2019 A single layer anti-reflection coating can be made non-reflective only at one wavelength, usually at the middle of the visible. The intersecting point of these two circles is labeled G, and vectors CG and GO are depicted. The refractive indices and optical thicknesses of the respective layers of the present invention are set forth as follows: The first layer consists of material selected from a group comprising MgF2, LaF2, Na3 (AlF4) and SiO2. In order to act a single layer as an ARC layer to obtain net zero reflection in the spectral range of 300–1200 nm, the amplitudes of the reflected waves at the air-ARC interface and ARC-substrate interface have to be identical and precisely one-half wave (180°) out of phase, resulting in destructive interference. Multi-Layer Anti-Reflection Coatings. The samples were then annealed at 140 °C for 30 min to remove the residual solvent. The anti-reflection coating is produced by evaporating a mixture of ZrO2 and TiO2 for the fourth layer, Al2 O3 for the third layer, a mixture of ZrO2 and TiO2 for the second layer, and MgF2 for the first layer in that order on the surface of the preselected glass substrate.