This paper reports an extensive analysis of the potential-induced degradation (PID) of N-type bifacial solar cells. The analysis is based on combined electrical characterization, electroluminescence ...and external quantum efficiency measurements, carried out on solar cells submitted to high PID stresses. We investigate the impact of two different encapsulation materials: (i) polyolefin elastomer (POE) and (ii) ethylene-vinyl-acetate (EVA). We describe the degradation and recovery kinetics as a function of the temperature and the stress voltage. Moreover we demonstrate that the POE can be adopted to reduce the decrease of conversion efficiency during PID stresses. Finally we investigate the effects of PID with an optical analysis in order to find the main cause of the performance degradation.
•We develop N-type bifacial solar cells with different encapsulation materials.•We investigate the reliability of bifacial solar cells subjected to potential induced degradation on rear and front sides of a solar module.•We investigate the potential induced degradation at different voltages and temperatures.•We demonstrate that the use of different encapsulants may result in different reliability to PID.•We investigate the effects of PID with optical analyses (electroluminescence and external quantum efficiency).
This paper reports on the impact of soft- and hard-switching conditions on the dynamic ON-resistance of AlGaN/GaN high-electron mobility transistors. For this study, we used a special double pulse ...setup, which controls the overlapping of the drain and gate waveforms (thus inducing soft and hard switching), while measuring the corresponding impact on the ON-resistance, drain current, and electroluminescence (EL). The results demonstrate that the analyzed devices do not suffer from dynamic R ON increase when they are submitted to soft switching up to V DS = 600 V. On the contrary, hard-switching conditions lead to a measurable increase in the dynamic ON-resistance (dynamic-R ON ). The increase in dynamic R ON induced by hard switching is ascribed to hot-electrons effects: during each switching event, the electrons in the channel are accelerated by the high electric field and subsequently trapped in the AlGaN/GaN heterostructure or at the surface. This hypothesis is supported by the following results: 1) the increase in R ON is correlated with the EL signal measured under hard-switching conditions and 2) the impact of hard switching on dynamic R ON becomes weaker at high-temperature levels, as the average energy of hot electrons decreases due to the increase scattering with the lattice.
We review the failure modes and mechanisms of gallium nitride (GaN)-based light-emitting diodes (LEDs). A number of reliability tests are presented, and specific degradation mechanisms of ...state-of-the-art LED structures are analyzed. In particular, we report recent results concerning the following issues: 1) the degradation of the active layer induced by direct current stress due to the increase in nonradiative recombination; 2) the degradation of LEDs submitted to reverse-bias stress tests; 3) the catastrophic failure of advanced LED structures related to electrostatic discharge events; 4) the degradation of the ohmic contacts of GaN-based LEDs; and 5) the degradation of the optical properties of the package/phosphors system of white LEDs. The presented results provide important information on the weaknesses of LED technology and on the design of procedures for reliability evaluation. Results are compared with literature data throughout the text.
We present a comprehensive review and outlook of silicon carbide (SiC) and gallium nitride (GaN) transistors available on the market for current and next-generation power electronics. Material ...properties and structural differences among GaN and SiC devices are first discussed. Based on the analysis of different commercially available GaN and SiC power transistors, we describe the state-of-the-art of these technologies, highlighting the preferential power conversion topologies and the key characteristics of each technological platform. Current and future fields of application for GaN and SiC devices are also reviewed. The article also reports on the main reliability aspects related to both technologies. For GaN HEMTs, threshold voltage stability, dynamic ON-resistance, and breakdown limitation are described, whereas for SiC MOSFETs the analysis also focuses on gate oxide failure and short-circuit (SC) robustness. Finally, we give an overview on the perspective of such materials in different fields of interest. An indication of possible future improvements and developments for both technologies is drawn. The requirements for hybrid converters, along with a careful optimization of performance and the use of innovative optimization tools, are underlined.
This paper reports on the degradation mechanisms that limit the reliability of high-power light-emitting diodes (LEDs) for lighting applications. The study is based on the experimental ...characterization of state-of-the-art LEDs fabricated by leading manufacturers. We demonstrate that, despite high potential reliability, high-power LEDs may suffer from a number of degradation mechanisms that affect the stability of the blue semiconductor LED chip and of the phosphor layer used for the generation of white light. More specifically, we describe the following relevant mechanisms: 1) the optical degradation of LEDs, due to an increase in the nonradiative recombination rate, which can be correlated to modifications in the forward-bias current-voltage characteristics; 2) the variation in forward voltage, due to the increase in series resistance; 3) the optical degradation of phosphor layers used for blue-to-white light conversion; and 4) the failure of LEDs submitted to "hot plugging," which is the direct connection of an LED chain to an energized power supply, due to the generation of high current spikes. Results provide an overview on the failure mechanisms that limit the reliability of state-of-the-art LEDs and on the role of current and temperature in determining the failure of the devices.
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