Enhancing Device Performance of CZTSSe Thin Film Solar Cells with IZO by Controlling Substrate Temperature

Transparent conductive oxide (TCO) is a material used in various optoelectronic fields such as displays, sensors, automobiles, and solar cells. In these applications, the TCO used as the window layer of solar cells must have high transmittance to transmit light to the absorption layer. TCO must also have good electrical properties to ensure smooth transport of charge carriers. Among various materials, Indium Tin Oxide (ITO) is preferred in various fields because it has excellent electrical conductivity in the visible light region, excellent optical transmittance, low electrical resistance, and wide band gap. However, achieving the high electrical and optical properties of ITO requires relatively high deposition temperatures, which can degrade the performance of the base material. Indium Zinc Oxide (IZO) has been attracting attention as an alternative due to its favorable electrical conductivity, high optical transmittance, and wide work function. Furthermore, IZO can be deposited at low power and low temperature, and it has low absorption at long wavelengths.<br/>In this study, IZO thin films were deposited on soda-lime glass (SLG) using RF magnetron sputtering. The deposition was conducted at temperature RT, 100 °C, 170 °C, 230 °C, and 300 °C, respectively. Especially, the thin film deposited at 170 °C showed a high transmittance of 86.4% and a low sheet resistance of 12.97 Ω/sq in the visible light region. Also, an IZO transparent electrode was applied to the actual Cu₂ZnSn(S,Se)₄ (CZTSSe) thin film solar cells (TFSCs) devices as a window layer, and the device parameters and EQE of the solar cells were analyzed systematically. The CZTSSe TFSCs with IZO TCO layer deposited at 230 °C show a power conversion efficiency (PCE) of 6.85%. Surprisingly, the CZTSSe TFSCs without i-ZnO deposited at RT show PCE of 9.83% with V_oc of 481 mV, <i>J</i>_sc of 30.5 mA/cm², and FF of 66.9% respectively.