SYNTESIS OF ZN1-XSNXO (ZTO) BUFFER LAYER USING SOLUTION PROCESS SPIN COATING METHOD ON SOLAR CELLS CU2ZNSNS4 (CZTS)

• Main Author: Refantero, Gema
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67158
• Institution: Institut Teknologi Bandung

Cu2ZnSnS4 material (CZTS) is an excellent material to be applied as an absorber layer to thin-film solar cells because it has a high similarity with The Cu(In,Ga)S2 (CIGS) material, where CIGS solar cell is a type of solar cell that has developed since 1976 which at this time has achieved cell efficiency of more than 20%. It has a direct band gap (1.0 – 1.5 eV) with an absorption coefficient of 104 - 105 cm-1. And it has a high hole density, which is about 1016 cm-3. Of these various potentials, unfortunately CZTS solar cells still use toxic materials, namely Cadmium which is used in the supporting layer, n-type buffer layer. CdS also has a low band gap (2.4 – 2.5 eV), so the use of CdS as a buffer layer can reduce absorption at low wavelengths. To solve this problem, a material with a higher band gap (~3.0 – 3.7 eV) is needed. Thus, several researchers have conducted studies and analyzes of several alternative materials that can replace CdS. ZnSnO (ZTO) material has excellent potential to become a material that can replace Cadmium as a buffer layer on CZTS solar cells. However, from these various studies, ZTO materials were synthesized using the vacuum method which is relatively more expensive and uses more complex technology than using the non-vacuum solution process method. In this study, optimization of ZTO material was carried out as a buffer layer for CZTS solar cells synthesized using the spin coating method. Optimization is carried out by varying the thickness of the ZTO material layer and the variation in the Zn:Sn ratio in the ZTO precursor composition with variations of 2:1, 3:1, 4:1, and 5:1. the ZTO buffer layer is formed in the amorphous phase, which is characterized by the non-formation of a single peak in the XRD pattern. This is reinforced by looking at the results of SEM characterization which shows the surface morphology of the ZTO buffer layer which has a grain size of ~50 nm with high uniformity. The formation of ZTO as an amorphous phase makes it an advantage for the ZTO buffer layer, because with this the ZTO buffer layer can be formed uniformly and has high stability on a large area. Buffer layer optimization is carried out by varying the deposition thickness by 3x, 5x, and 7x and the ratio of Zn:Sn with variants 2:1, 3:1, 4:1 and 5:1. From the results of variations in the deposition thickness of the ZTO layer obtained by analyzing the results of UV-Vis Spectroscopy characterization using the Tauc plot method, ZTO layers were obtained which were deposited 3x, 5x, and 7x respectively had band gap values of 3.88 eV, 3.87 eV, and 3.86 eV which showed a decrease in the band gap of 0.01eV per repetition of spin coating deposition. The results of variations in the ratio of Zn:Sn with variants 2:1, 3:1, 4:1 and 5:1 respectively have band gap values of 3.88 eV, 3.28 eV, 2.97 eV, and 2.39 eV. From this result it can be implied that an increase in the Zn/Sn ratio in a thin layer of ZTO can reduce the band gap value of the ZTO material and from the results of this variation can be taken the optimum value of the ZTO gap band resulting from the ratio of the Zn:Sn element of 3:1. From the comparison of Light Harvesting Efficiency (LHE) CZTS absorbent layers, CdS and ZTO buffer layers. The CZTS-ZTO p-n pair has better compatibility compared to the CZTS-CdS p-n pair, which is seen from the absence of LHE overlapping for the CZTS-ZTO pair in the very large wavelength range of 400-790 nm. As for the CZTS-CdS pair, there is a fairly high LHE overlapping in the range of 300-500nm by 80% by CdS. Which will further minimize the light that can be absorbed by the CZTS absorber layer.