Impact of Temperature Optimization of ITO Thin Film on Tandem Solar Cell Efficiency

Abstract

This study examined the impact of temperature optimization on indium tin oxide (ITO) films in monolithic HJT/perovskite tandem solar cells. ITO films were deposited using magnetron sputtering at temperatures ranging from room temperature (25 °C) to 250 °C. The sputtering target was ITO, with a mass ratio of In₂O₃ to SnO₂ of 90% to 10%. The effects of temperature on the ITO film were analyzed using X-ray diffraction (XRD), spectroscopic ellipsometry, and sheet resistance measurements. Results showed that all ITO films exhibited a polycrystalline morphology, with diffraction peaks corresponding to planes (211), (222), (400), (440), and (622), indicating a cubic bixbyite crystal structure. The light transmittance exceeded 80%, and the sheet resistance was 75.1 Ω/sq for ITO deposited at 200 °C. The optical bandgap of deposited ITO films ranged between 3.90 eV and 3.93 eV. Structural and morphological characterization of the perovskite solar cell was performed using XRD and FE-SEM. Tandem solar cell performance was evaluated by analyzing current density-voltage characteristics under simulated sunlight. By optimizing the ITO deposition temperature, the tandem cell achieved a power conversion efficiency (PCE) of 16.74%, resulting in enhanced tandem cell efficiency.

Keywords: deposition temperature; indium tin oxide (ITO); perovskite; silicon heterojunction; tandem solar cell.

Figure 1

HJT solar cell (2.5 × 2.5 cm²) (a), HJT/perovskite tandem solar cell (active area: 1.45 cm²) (b), thin film colors and deposition methods (c), HJT/perovskite tandem solar cell eV diagram (d).

Figure 2

XRD patterns of ITO-RT, ITO-150, ITO-175, ITO-200, and ITO-250 films samples.

Figure 3

Texture coefficients (TC) of ITO films produced at different temperatures calculated from XRD patterns.

Figure 4

Optical transmittance spectra versus wavelength for ITO deposited on glass substrates via the PVD system at ITO-RT, ITO-150, ITO-175, ITO-200, and ITO-250 different temperatures.

Figure 5

Optical reflectance spectra of ITO films deposited on glass substrates via the PVD system at ITO-RT, ITO-150, ITO-175, ITO-200, and ITO-250 temperatures, plotted against wavelength.

Figure 6

Band gap measurement of ITO deposited at different temperatures, obtained by plotting hν versus (αhν)². The optical band gap of the deposited ITO films was calculated to be between 3.90 eV and 3.93 eV (The band gap was calculated using fitted curves, which are represented by dashed lines in the figure).

Figure 7

Sheet resistance, FOM, and resistivity graph of ITO films as a function of the temperature. The FOM values calculated from Haacke’s method [49], which optimally characterized the optical and electrical properties of ITO films through electrical sheet resistance and optical transmittance.

Figure 8

Current density (J)-voltage (V) graphs of HJT solar cells with ITO layers deposited at different temperatures: ITO-RT, ITO-150, ITO-175, ITO-200, and ITO-250.

Figure 9

The XRD results for the monolithic c-Si heterojunction perovskite tandem solar cell, including a focus on the top cell.

Figure 10

c-Si HJT/perovskite tandem solar cell SEM images. (a) Random pyramid-structured n-type c-Si and area with perovskite solar cell, (b) cross-section view of tandem layers and thickness (the yellow circles), (c) the cross-section of HJT solar cell, (d) top perovskite cell structure.

Figure 11

A comparison of the efficiency of a monolithic tandem solar cell comprising n-type c-Si/ITO/SnO₂/CH₃NH₃PbI₃−xClx/Spiro-OMeTAD/ITO/Ag and a c-Si HJT solar cell is presented. The tandem solar cell’s conversion efficiencies utilizing ITO deposited at room temperature and 200 °C are designated as Tandem-RT (15.78%) and Tandem-200 (16.74%), respectively.