Photolithography Technologies for Metallic Meshes and Local Contacts on CIGS Thin Film Solar Cells with NIR-Transparent TCO Layers

A transparent conducting oxides(TCO) for CIGS thin film solar cells, Al-doped ZnO(AZO) is widely used because of their wide band gap energy(Eg = 3.37 eV), high optical transparency, conductivity and based on earth-abundant materials. However, for the application of TCO layer for modules fabrication, AZO has an issue about optical loss in the visible and near-infrared spectrum. This causes electrical, optical and fill factor(FF) losses in the integration of solar cells in a module, which is known as cell to module(CTM) losses. To solve those issues, we have fabricated CIGS solar cells with hybrid electrodes of metallic grids / TCO layers.<br/>Photolithography is versatile technology to make the patterns as we desired and demanded for semiconductor devices. We have patterned metallic meshes on AZO layer of CIGS solar cells using by photo lithography technique with negative photoresists. We fabricated photoresist template by exposure and development processes and deposited aluminum or silver metallic layers on the template about 1 μm of thickness and lifted off the photoresists to complete metallic meshes with attempting to minimize the linewidth by 2~3 μm and also minimize transmittance loss controlling by grid distance about 100 to 200 μm.<br/>As a result, Al meshes occupying from 2.20 to 2.84% in a cells whereas reference devices have 3.94 to 4.66 % of grid area. In both case of Al and Ag meshes devices, Jsc has been improved to 27.98 mA/cm² than 27.73 mA/cm² of the reference devices. In the case Ag meshes devices, Voc has been improved to 0.65 V which is closer to 0.66 V of the reference cell. By these results, we will discuss how to fabricate the solar cells with composite transparent electrode better way.<br/>On the other hand, we have fabricated Hydrogen-doped Indium Oxide(In₂O₃:H) by sputtering process with H₂ and O₂ reactive gases with various mass flow controlling to improve NIR transmittance and high mobility. We have fabricated CIGS solar cells with In₂O₃:H instead of AZO layer and compare the parameters to clarify how NIR transparency and mobility improves the power conversion efficiencies.<br/>Also, we fabrcated local contacts with MgF₂ passivation layer with dot-shaped local contacts with various diameters and spacings on Mo back contact before CIGS deposition. we will discuss how those diameter and distance affecting on solar cells power conversion efficiency improvements.