Heinrich Christoph Neitzert

This work explores the possibility of using 4H-SiC PIN diodes to provide a high electric field able to induce the Stark effect in ⁷Be atoms implanted in the diode space charge region, modifying the ⁷Be radioactive decay time. A set of PIN diodes of area ranging between 2.12 × 10⁻³ cm² and 9.88 × 10⁻³ cm² was designed and fabricated to reach breakdown voltages up to 1000 V. Be ions were implanted in the epitaxial layer, and then the devices were reverse biased at about 75% of the theoretical breakdown voltage for durations exceeding 100 days, long enough for a precise measurement of the ⁷Be radioactive decay time. Electrical characterization in the pristine state, after Be ion implantation, and after long reverse bias allowed us to verify the suitability of 4H-SiC PIN diodes by assessing both the agreement between simulated and measured performance and the stability of the electric field. Be ion implantation-related defects induced both an increase in the reverse current generation and a decrease in the junction capacitance, though not affecting the breakdown voltage. Comparison with test devices implanted with the stable isotope ⁹Be indicates that any defects introduced by the ⁷Be radioactive decay are below the detection limit of the employed characterization techniques and have a negligible impact on the reverse-blocking characteristics of the diodes. Device simulations allowed us to conclude that the electric field remains close to its theoretical value throughout the experiment duration, confirming the suitability of 4H-SiC diodes for both induction and measurement of ⁷Be lifetime variations.

This study presents the design, fabrication, and electrical characterization of 4H-SiC PIN diodes employed to provide a high electric field able to induce Stark effect in ⁷ Be atoms implanted in the space charge region. Indeed, a variation in the half-life of the ⁷ Be radioactive decay is expected to be achieved by applying an electric field of the order of 10 ⁶ V/cm, which can be produced by reverse-biasing 4H-SiC diodes close to the breakdown voltage. A set of diodes of area ranging between 2.12×10 ^-3 cm ² and 9.88×10 ³ cm ² was designed and fabricated to reach breakdown voltages up to 1000 V. When tested under reverse current limitation set equal to 300 nA, over 50% out of 24 devices could withstand reverse bias exceeding 800 V. This work reports on the characteristics of one diode of 9.88×10 ³ cm ² area, implanted with ⁷ Be and subject to continuous reverse-bias at 750 V for 107 days. Electrical characterization conducted before, during, and after long-term polarization highlighted an increase in the reverse current generation due to implantation-related defects, which however does not affect the breakdown voltage. These considerations lead to the conclusion that the electric field acting on the implanted ⁷Be remains stable over time, confirming the suitability of 4H-SiC diodes for both induction and measurement of ⁷ Be lifetime variations.

Inserting point contacts between the perovskite and C₆₀ layers reduces the interfacial recombination. However, the accumulation of mobile ions at the point contacts can decrease the device stability.

The influence of high energy proton irradiation on the charge carrier kinetics in triple cation, triple halide semiconducting perovskite films with applications in medical instrumentation and space photovoltaics has been investigated with the contactless Time Resolved Microwave Conductivity Measurement technique. In the first experiment, the high sensitivity of the measurement setup for the characterization of the silicon solar cell degradation under the same optical excitation conditions has been demonstrated. Regarding the excess charge carrier kinetics after pulsed excitation in perovskite films, it is found that the TRMC transients are not following a single exponential decay. In contrast to the results on crystalline silicon only minor changes of the charge carrier decay are observed in these perovskite films after proton irradiation. It has also been shown, that the technique can be used to check for the efficient surface passivation of the perovskite films with PEAI layers. The stability of this passivation under irradiation has been investigated and a more pronounced change of the decay time is found for the passivated films as compared to the non-passivated film. The results of these TRMC measurement have been compared to the properties of solar cells, using the same substrates and thin films layers as absorption layers. A good correlation between the transient measurements with the external quantum efficiency spectra, obtained from the solar cell characterization has been found.

In this work, we fabricate & test MA-free co-evaporated perovskite solar cells that could potentially be fabricated in space. Pseudo-JV characteristics & electroluminescence hereby help to distinguish radiation damage from parasitic effects.

The emission of off-odors from mechanically recycled plastics severely limits their re-introduction into the market for the production of new objects, for the same use or even for less demanding applications, thus hindering the implementation of an effective circular economy for plastics. The addition of adsorbing agents during the extrusion of polymers represents one of the most promising strategy to reduce the odorous emissions of plastics, due to its characteristics of cost-effectiveness, flexibility and low energy consumption. The novelty of this work lies in the assessment of zeolites as VOC adsorbents during the extrusion of recycled plastics. They appear more suitable than other types of adsorbents, due to their ability to capture and “hold” the adsorbed substances at the high temperatures of the extrusion process. Moreover, the effectiveness of this deodorization strategy was compared with the traditional degassing technique. Two types of mixed polyolefin wastes, coming from completely different collection and recycling processes, were tested: Fil-S (Film-Small), deriving from post-consumer flexible films of small size, and PW (pulper waste), which is the residual plastic waste obtained from the paper recycling process. The melt compounding of the recycled materials with two micrometric zeolites (zeolite 13X and Z310) resulted as more effective in the off-odors removal with respect to degassing. In particular, the highest reduction (−45%) of the Average Odor Intensity (AOI) was measured for both PW/Z310 and Fil-S/13X systems at 4 wt% of the zeolites’ amount, compared with the corresponding untreated recyclates. Finally, by combining degassing and melt compounding with zeolites, the best result was obtained for the composite Fil-S/13X, whose Average Odor Intensity resulted as quite close (+22%) to the one of the virgin LDPE.

Noise spectroscopy is essentially focused on the investigation of electric fluctuations produced by physical mechanisms intrinsic to conductor materials. Very complex electrical transport phenomena can be interpreted through the study of the fluctuation properties, which provide interesting information both from the point of view of basic research and of applications. In this respect, low-frequency electric noise analysis was proposed more than twenty years ago to determine the quality of solar cells and photovoltaic modules, and, more recently, for the reliability estimation of heterojunction solar cells. This spectroscopic tool is able to unravel specific aspects related to radiation damage. Moreover, it can be used for a detailed temperature-dependent electrical characterization of the charge carrier capture/emission and recombination kinetics. This gives the possibility to directly evaluate the system health state. Real-time monitoring of the intrinsic noise response is also very important for the identification of the microscopic sources of fluctuations and their dynamic processes. This allows for identifying possible strategies to improve efficiency and performance, especially for emerging photovoltaic devices. In this work are the reported results of detailed electrical transport and noise characterizations referring to three different types of solar cells (silicon-based, organic, and perovskite-based) and they are interpreted in terms of specific physical models.