Understanding the effect of the interlayers on the ultrasonic spray coating of perovskite in CIGS-perovskite tandem solar cells

Perovskites are widely regarded as promising absorber materials for next-generation thin-film solar cells. Their exceptionally high absorption coefficient allows the fabrication of very thin absorber layers (~600 nm), in contrast to the ~100-micron thick silicon absorbers used in conventional photovoltaics (PV). This enables the development of thin-film solar cells that are lightweight, flexible, and potentially semi-transparent. Combining a perovskite top cell with a proven thin-film PV technology like CIGS offers the potential to create a highly efficient, fully thin-film tandem solar cell. The theoretical efficiency of such a tandem architecture can exceed 40%, far surpassing the ~30% efficiency limit of single-junction devices.

Achieving such high efficiencies in practice, however, remains challenging. A key bottleneck lies in the selection and design of suitable interlayers. In two-terminal CIGS-perovskite tandem solar cells, these interlayers play dual roles. First, they form the recombination junction, electrically connecting the CIGS bottom cell with the perovskite top cell, and must facilitate efficient charge recombination. Second, they serve as the substrate for perovskite deposition, making them equally critical for successful film formation during fabrication. Therefore, understanding how interlayer characteristics—such as surface roughness, surface energy, and chemical composition—affect perovskite film growth is essential.

Ultrasonic spray coating is a promising, scalable deposition technique particularly suited for perovskite deposition onto rough CIGS surfaces. It involves spraying micron-sized droplets directly onto the sample, making it well-suited for depositing perovskite on top of CIGS substrates. At EnergyVille, this technique has enabled the fabrication of single-junction perovskite solar cells with efficiencies exceeding 16%.[1] Furthermore, in-house CIGS-perovskite tandem devices have achieved efficiencies approaching 20%.[2] However, this gain is still far below the theoretical potential of tandems and represents only a modest improvement over their perovskite single-junction counterparts. Non-conformal perovskite coverage often results in pinholes and cracks, leading to shunting paths and low fill factors. Gaining deeper insight into the relationship between interlayer properties and spray-coated perovskite film formation is therefore vital to achieving uniform coverage, high-quality absorber layers, and ultimately, improved tandem performance.

This master thesis will investigate how the physical and chemical properties of interlayers influence the nucleation, crystallization, and final morphology of spray-coated perovskite films. Using a fixed CIGS bottom cell as a starting point, the student will fabricate multiple CIGS|interlayer|perovskite stacks, with the perovskite layer deposited via ultrasonic spray coating. The resulting perovskite layers will be characterized using structural, morphological, and optoelectronic techniques such as SEM, XRD, PL, and TRPL. The goal is to correlate interlayer properties with perovskite film quality. Depending on the student’s interest, the impact of interlayer properties on final device performance can also be explored.

This project provides hands-on experience in thin-film deposition, solar cell fabrication, and advanced characterization techniques. The student will work in the state-of-the-art laboratory environment of EnergyVille 2, joining a leading international research team specializing in perovskite and tandem photovoltaics. Motivation and the ability to work independently are expected.

[1] Silvano, J., Hamtaei, S., Verding, P., Vermang, B., & Deferme, W. (2023). Investigating the Fabrication of Perovskite Solar Cells by Ultrasonic Spray Coating: A Design of Experiments Approach. ACS Applied Energy Materials, 6(14), 7363-7376.
[2] Silvano, J., Birant, G., Oris, T., D’Haen, J., Deferme, W., & Vermang, B. (2024). Ultrasonic spray coating for the scalable fabrication of Perovskite-on-Chalcogenide monolithic tandem Devices: Approaching the 20% efficiency. Solar Energy, 277, 112738.

Type of Project: Combination of internship and thesis

Master's degree: Master of Engineering Science

Master program: Chemistry/Chemical Engineering; Materials Engineering; Nanoscience & Nanotechnology; Physics

Duration: 6-9 months

Supervisor: Bart Vermang (UHasselt)

For more information or application, please contact the supervising scientist Joost Caeyers (joost.caeyers@imec.be).

Only for self-supporting students.