Degradation mechanism analysis in temperature stress tests on III–V ultra-high concentrator solar cells using a 3D distributed model

Abstract

A temperature stress test was carried out on GaAs single-junction solar cells to analyze the degradation suffered when working at ultra-high concentrations. The acceleration of the degradation was realized at two different temperatures: 130 °C and 150 °C. In both cases, the degradation trend was the same, and only gradual failures were observed. A fit of the dark l-V curve at 25 °C with a 3D distributed model before and after the test was done. The fit with the 3D distributed model revealed degradation at the perimeter because the recombination current in the depletion region of the perimeter increased by about fourfold after the temperature stress test. Therefore, this test did not cause any morphological change in the devices, and although the devices were isolated with silicone, the perimeter region was revealed as the most fragile component of the solar cell. Consequently, the current flowing beneath the busbar favors the progression of defects in the device in the perimeter region.

Novel accelerated testing method for III–V concentrator solar cells

“…3 we can see that the degradation of the dark I-V curve is at low voltages range. To determine the degradation mechanism, a simulation of the dark I-V curve using a computational 3D model method based on distributed circuital units has been done [14]. This analysis reveals that the degradation takes place in the perimeter region since the recombination current density in depletion region at the perimeter increases a factor 4.…”

3-D modeling of perimeter recombination in GaAs diodes and its influence on concentrator solar cells

“…Because of the complexity of the triple junction solar cells (GalnP/GalnAs/ Ge), it is recommendable to start analysing each subcell independently. So far, the most studied subcell has been the middle cell by analysing the GaAs single junction diode [1][2][3][4]. It must be taken into account that because of the negligible composition of indium (1-2%) of the GalnAs middle cell, the analysis of single junction GaAs cells grown on GaAs substrates is a valid approach in order to extract conclusions for the triple junction cells.…”

“…In addition to the usefulness of understanding the GaAs cell perimeter recombination for multijunction solar cells, the recent proposal of using GaAs single junction solar cells for competitive cost of photovoltaic electricity [5] adds interest to this study. It is well known that, as the perimeter-area (P/A) ratio increases, the perimeter current reaches significant values that can lead to a decrease in the open circuit voltage and to an important contribution to degradation mechanisms in GaAs solar cells [1]. Therefore, the performance of small size solar cells such as the most ones used in concentration applications can be affected by perimeter recombination.…”

“…The surface states energy levels can have a strong effect on the electrical characteristics of the semiconductor because the ionic charges on or outside the semiconductor surface induce image charges in the semiconductor causing the formation of the so-called surface channel or surface depletion-layer which is a region where minority carriers can be confined. Once this channel is formed it gives rise to a surface leakage current [7], Perimeter recombination in GaAs diodes, transistors and solar cells has been experimentally analyzed and modeled by using 1-D and 2-D (one and two dimension) approaches by several authors [1][2][3][4]8,9]. The first approximation to describe this phenomenon was made by Henry et al [8].…”

“…The first approximation to describe this phenomenon was made by Henry et al [8]. They proposed an analytical expression (1) to obtain the perimeter current assuming: (a) Fermi level pinning and (b) constant electron and hole densities at the surface.…”