Structure, Electrical and Optical Properties of ITO Thin Films and their Influence on Performance of CdS/CdTe Thin-Film Solar Cells

TL;DR

This study investigates how the thickness of ITO thin films affects their structural, electrical, and optical properties, and how these properties influence the efficiency of CdS/CdTe solar cells, finding optimal performance at 325 nm thickness.

Contribution

It provides a comprehensive analysis of ITO film properties at various thicknesses and their direct impact on the performance of CdS/CdTe solar cells, including experimental and modeling approaches.

Findings

Increased ITO thickness leads to larger crystallite and grain sizes.

Resistivity decreases with increasing film thickness.

Maximum solar cell efficiency achieved at 325 nm ITO thickness.

Abstract

In terms of mixing graded TiO2 and SnO2 powders by solid-state reaction method, ITO was prepared. Using electron beam gun technology, ITO films with different thicknesses were prepared. The influence of film thickness on structure, electrical and optical properties was studied. The XRD patterns were utilized to determine the structural parameters (lattice strain and crystallite size) of ITO with different thicknesses. It is observed that the average crystallite size increases as the film thickness increases, but the lattice strain decreases. SEM shows that as the film thickness increases, the grain size of ITO increases and improves. The electrical properties of ITO films with different thicknesses were measured by the standard four-point probe method. It can be seen that as the thickness of the ITO film increases from 75 nm to 325 nm, the resistivity decreases from 29x10^-4 Ohm/cm to 1.65x10^-4 Ohm/cm. This means that ITO films with lower electrical properties will be more suitable for high-efficiency CdTe solar cells. Three optical layer models (adhesive layer of the substrate/B-spline layer of ITO film/surface roughness layer) are used to calculate the film thickness with high-precision ellipsometry. In the higher T(lambda) and R(lambda) absorption regions, the absorption coefficient is determined to calculate the optical energy gap, which increases from 3.56 eV to 3.69 eV. Finally, the effects of ITO layers of various thicknesses on the performance of CdS/CdTe solar cells are also studied. When the thickness of the ITO window layer is 325 nm, Voc = 0.82 V, Jsc = 17 mA/cm2, and FF = 57.4%, the highest power conversion efficiency (PCE) is 8.6%.