Effect of electron transport layer thickness and characteristics behaviour of hybrid copper indium gallium selenide thin film solar cells

Abstract

Copper Indium Gallium Selenide (CIGS) thin-film solar cells are pivotal due to their remarkable absorption coefficient and significant potential for cost-effective solar energy conversion. A key factor influencing their performance is the thickness of the electron transport layer (ETL). This study examines the impact of varying zinc oxide (ZnO) ETL thicknesses of 25, 50, 75, and 100 nm within a structured CIGS solar cell configuration of Fluorine-doped Tin Oxide (FTO)/ZnO/CIGS/Molybdenum Diselenide (MoSe₂)/Molybdenum (Mo), fabricated using advanced radio frequency (RF) magnetron sputtering techniques. By exploring the relationship between ZnO ETL thickness and solar cell performance, we provide valuable insights into optimizing these technologies. X-ray diffraction analysis reveals the successful formation of various solar cell layers, showcased by distinct peaks in the diffraction pattern. Among the tested configurations, the 75 nm ZnO ETL shines through as the most effective, demonstrating superior optical and electrical properties compared to the thinner layers. Notably, the 75 nm ZnO ETL not only achieves a crystalline size of 42 nm and a transmittance of 55 % at an 800 nm wavelength but also delivers impressive electrical performance, with a short-circuit current density (Jsc) of 35.1 mA/cm² and an open-circuit voltage (Voc) of 0.81 V. Furthermore, it exhibits strong absorption coefficients of 5.5 × 10⁴ cm⁻¹ at 3.5 eV and 8.1 × 10⁴ cm⁻¹ at 4.0 eV, along with a refractive index of 2.05. Additionally, with a conductivity of 0.45 × 10⁻³ S/cm and a resistivity of 2.22 × 10² Ω cm, this configuration underscores the potential for enhanced charge transport, light absorption, and overall efficiency in CIGS solar cells, making it a promising candidate for advancing solar technology. Moreover, increasing the ZnO ETL thickness in CIGS was found to improve thermal stability and improved conductivity at the cost of reduced transparency.