The research conducted in this activity line has led to significant advancements in Concentrated Photovoltaics (CPV) technology, particularly in the development of 4-junction cells based on the integration (within the same MOCVD growth chamber) of III-V compounds with those from Group IV, and has highlighted some challenges. During the research, RSE discovered that tin is responsible for the degradation of the morphology of III-V compounds when using Ge as a substrate. In line with these findings, spectral response simulations of GaAs/SiGeSn devices have shown a high recombination velocity at the GaAs and SiGeSn interface (>10^5 cm/sec). To overcome this issue, Bis(cyclopentadienyl) Magnesium (Cp2Mg) and Trimethyl Gallium (TMGa) were identified as sources for p-type doping of Group IV compounds. N-type doping was achieved through contamination of the growth chamber from III-V compounds.

Additionally, the structure of single-junction InGaP and AlInGaP cells suitable for integration into luminescent modules was optimized, resulting in a 20% increase in short-circuit current and a 3% increase in open-circuit voltage.

For the development of the 4-junction, 3-terminal device, RSE implemented the MESA etch process, which allows for the deposition of a third “deep” electrical contact.

To reduce the materials required for device fabrication, and thus the device cost, the TAIKO thinning technique of the Ge substrate was tested. The process for separating CPV cells from the original wafer was also refined by identifying suitable cutting parameters.

In collaboration with the Department of Physics at the University of Pavia, the study of anti-reflective coatings (ARC) based on Ta2O5/SiO2, Nb2O5/SiO2, and mixed (Nb2O5)x(SiO2)y compared to (Ta2O5)x(SiO2)y and GaN continued. A notable finding is that ARC sputtering was successfully performed on InGaP cells without degrading the performance of the devices.

For structural characterization of the materials, high-resolution X-ray diffraction was used, while Electrochemical Capacitance-Voltage techniques were employed to study doping. Additionally, a high-resolution spatial study of electrical properties was conducted.