In the context of research activities aimed at increasing the efficiency of concentrator photovoltaic (CPV) systems, the development of diagnostic techniques applied to photovoltaic devices plays a crucial role. Diagnostics provide essential information for evaluating solar cells and the production process, both in terms of achievable performance and in identifying any anomalies in the manufacturing processes of these photovoltaic devices.

Among these diagnostic techniques, measuring Spectral Response and Quantum Efficiency, which involves the current produced by the photovoltaic cell at different wavelengths, is particularly important. Unlike single-junction photovoltaic cells, characterizing multi-junction (MJ) cells is more complex, as it requires precise light biasing to accurately characterize the individual sub-cells that specialize in converting solar radiation within a specific spectral band.

During the measurement of Spectral Response and Quantum Efficiency in multi-junction cells, a substantial continuous photocurrent is generated by the light bias, along with a weak modulated photocurrent that decreases with the number of junctions. However, this modulated component is essential for calculating Spectral Response and Quantum Efficiency. The overlap of these two components necessitates the extraction of the modulated component (partially completed in 2019), followed by an in-depth numerical analysis to filter out the superimposed noise. This latter task was the primary focus of this research, aimed at increasing the accuracy of Spectral Response and Quantum Efficiency measurements in MJ cells.

In this research line, the focus was on the numerical processing of the signal produced by the photovoltaic cell during measurement. Previously, RSE performed this processing with the help of a lock-in amplifier. However, this amplifier cannot be controlled via the LabVIEW software used for automating the measurement and therefore cannot be integrated into the Spectral Response and Quantum Efficiency measurement system currently under development, which aims to achieve full automation of this process. As a result, it was necessary to introduce a new numerical analysis system developed in the LabVIEW environment for instrument control. A data analysis program was then created, utilizing appropriate filtering techniques, including the Fourier Transform (FT).

To ensure measurement quality comparable to the existing system, the updated system was implemented using a data acquisition and processing system with a resolution of 16 bits for the amplitude of the acquired signals, compared to 12 bits in the previous system. Fine-tuning the data analysis algorithm required further modifications to the acquisition circuits to maximize the signal-to-noise ratio (S/N). This led to additional changes in the photodetection circuit.

To verify the new numerical signal analysis software, comparative tests were conducted with the previous acquisition system (lock-in amplifier). The results showed excellent agreement between the measurements obtained with the two techniques. This confirms the proper functioning of the newly developed numerical analysis system and allows for its integration into a program for the automated management of Spectral Response and Quantum Efficiency measurements of MJ cells, which will be completed in a subsequent activity. Finally, a system for controlling the temperature of the photovoltaic cell was developed, which will increase the reproducibility of the measurements.