Degradation Of Silicon Solar Cells Research Articles

Deciphering the Role of Hydrogen in the Degradation of Silicon Solar Cells under Light and Elevated Temperature

In recent years, significant attention has been paid to the research of light‐ and elevated‐temperature‐induced degradation (LeTID) in silicon solar cells due to the substantial power loss and instability it causes. It has been discovered that the presence of hydrogen is closely linked to the occurrence of LeTID. In this study, a thorough review and re‐assessment of previously published results is conducted and connected with newly obtained data. The findings indicate a complex interaction between different hydrogen complexes and the LeTID defect states. The precursor of LeTID is connected to molecular hydrogen (H2), while the LeTID degradation and regeneration are related to the binding of atomic hydrogen to the precursor and defect, respectively. A detailed description of the various reactions that occur under illumination and in the dark is provided. Additionally, explanation is given on how pre‐annealing can significantly affect the kinetics of LeTID during subsequent light soaking. Furthermore, a comprehensive hydrogen model that incorporates these various reactions and demonstrates an agreement between simulation and experimental results is developed. Finally, the implications of the findings on strategies for mitigating LeTID are discussed.

Research progress of light and elevated temperature-induced degradation in silicon solar cells: A review

At present, passivated emitter and rear cell (PERC) solar cells dominate the photovoltaic industry. However, light and elevated temperature-induced degradation (LeTID) is an important issue responsible for the reduction of PERC efficiency, which may lead to up to 16% relative performance losses in multicrystalline silicon solar cells, and this degradation occurs in almost all types of silicon wafers. Even in next-generation silicon solar cells like Tunnelling oxide passivated contact (TOPCon) and Heterojunction with Intrinsic Thin-layer (HJT) solar cells, LeTID can still cause an efficiency loss up to 1% relative. LeTID is a long process in terms of time during the whole cycle of degradation and regeneration, which will seriously affect the conversion efficiency and stability of solar modules, and hence increase the cost of electricity generated by solar cells. Furthermore, after years of research on LeTID, researchers are yet to determine the specific cause of LeTID. In this paper, we refer to specific literature, briefly describe the development history of LeTID, introduce the phenomena of LeTID in crystalline silicon solar cells, and describe its characteristics. In addition, we also analyzed the fundamental causes of LeTID, and found that the cause may be related to metal impurities or hydrogen contained in solar cells. At present, in view of the participation of hydrogen in LeTID and other existing related theories, this paper introduces several methods to inhibit LeTID in crystalline silicon. Finally, the content of this paper is summarized, and the development of solar cells in the future is prospected.

Progress in the understanding of light‐ and elevated temperature‐induced degradation in silicon solar cells: A review

AbstractAt present, the commercially dominant and rapidly expanding PV‐device technology is based on the passivated emitter and rear cell (PERC) design developed at UNSW. However, this technology has been found to suffer from a carrier‐induced degradation commonly referred to as ‘light‐ and elevated temperature‐induced degradation’ (LeTID) and can result in up to 16% relative performance losses. LeTID was recently shown to occur in almost every type of silicon wafer, independent of the doping material. Even though the degradation mechanism is known to recover under normal operation conditions, it is a lengthy process that drastically affects the energy yield, stability and, ultimately, the levelized cost of electricity (LCOE) of installed systems. Despite the joint effort of many research groups, the root cause of the degradation is still unknown. Here, we provide an overview of the existing literature and describe key LeTID characteristics and how these have led to the development of various theories of the underlying mechanism. Further, given the continuously appearing and strong evidence of hydrogen involvement in LeTID, many mitigation methods concerning hydrogenation have been suggested. We discuss such reported methods, bearing in mind crucial consumer necessities in terms of sustained cell performance and minimised LCOE.

Reducing potential induced degradation of silicon solar cells by using a liquid oxidation technique

An ultrathin layer of SiOx formed on the surface of a silicon solar cell can significantly reduce the potential induced degradation effect in solar cell modules. In this work, a liquid oxidation (LO) technique was developed to oxidize silicon surfaces by using a Ti/IrO2–CoO2 anode that can produce a large amount of hydroxyl radicals (•OH) and other species. Our results indicate that the LO SiOx (2.5 nm) layer is very dense, thus the modules made from LO treated cells are better able to mitigate potential induced degradation than modules made from ozone oxidized cells.

Effects of diffusion process on potential induced degradation of silicon solar cells.

Potential induced degradation (PID) has recently been identified as one of the most important degradation mechanisms for silicon solar cells. It is widely considered that PID is closely related with the manufacture and application period of solar modules. In this study, the effects of diffusion sheet resistance on PID were verified and explained by testing the emitter doping profile, the minority carrier lifetime, the emitter saturation current, the electrical performance of different cells, and the PID process. With increasing sheet resistance of cells, the depth and saturation current density of the emitter both decreased, and the cell efficiency increased, whereas the PID phenomenon became serious. It was found that higher sheet resistance or thinner P-N junction could lead to higher PID sensitivity. Therefore, more attention should be paid to PID phenomenon as the photovoltaic industry develops in the direction of high sheet resistance.

Light-induced Degradation of Silicon Solar Cells with Aluminiumoxide Passivated Rear Side

Light-induced degradation (LID) has been shown to significantly affect the performance of multicrystalline silicon (mc-Si) solar cells with aluminium oxide (AlOx) passivated rear side. Within this work, the impact of LID on the conversion efficiency of different silicon solar cell architectures with and without AlOx passivation is investigated. Under conditions representing realistic module operation, significant light-induced degradation of up to Δη = -2.9 %relin conversion efficiency has been observed for multicrystalline silicon (mc-Si)solar cells with AlOxpassivation. This degradation has been found to be higher than the degradation of, both,a mc-Si aluminium back surface field(Al-BSF) solar cell and, remarkably, a Czochralski-grown silicon (Cz-Si) solar cell with AlOx passivation. For a more detailed investigation of the interaction of mc-Si and AlOx passivation during degradation,a photoluminescence-based“effective defect”imaging has been performed on AlOx-passivated mc-Si lifetime samples. The local effective defect lifetimerelated to recombination due toLID-induced defects is found to vary strongly in the range of τeff,defect = 5 to 75 μs and, furthermore, areas with low effective lifetime could be identified as areas with relatively high dislocation density.

Thermal and electrical investigation of the reverse bias degradation of silicon solar cells

This work presents a detailed analysis of the degradation of Si-based solar cells submitted to reverse-bias stress; the study is based on electrical, electro-optical and thermal measurements, carried out at the different stages of the stress tests. The results show that exposure to reverse bias may induce severe modifications of the cell electro-optical performance: the most relevant failure mechanism is the increase in localized shunt resistance components. The changes in the leakage paths have been investigated both through infrared thermal imaging and SEM measurements.

Electronically stimulated degradation of silicon solar cells

Carrier lifetime degradation in crystalline silicon solar cells under illumination with white light is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both related to the most common acceptor element, boron, in silicon: (i) the dissociation of iron-boron pairs and (ii) the formation of recombination-active boron-oxygen complexes. While the first mechanism is particularly relevant in metal-contaminated solar-grade multicrystalline silicon materials, the latter process is important in monocrystalline Czochralski-grown silicon, rich in oxygen. This paper starts with a short review of the characteristic features of the two processes. We then briefly address the effect of iron-boron dissociation on solar cell parameters. Regarding the boron-oxygen-related degradation, the current status of the physical understanding of the defect formation process and the defect structure are presented. Finally, we discuss different strategies for effectively avoiding the degradation.

Method using the primary knock-on atom spectrum to characterize electrical degradation of monocrystalline silicon solar cells by space protons

In this work, a method to calculate the equivalent dose for orbits in which the main part of the damage is due to protons, is presented. The method compares the primary knock-on atom distribution and the depth dependence of damage for the cases of space-proton irradiation and laboratory irradiation of silicon solar cells, as obtained from simulations using the transport of ions in matter code. It is shown that, in order to simulate the right depth damage distribution in space for a solar cell covered by glass, it is convenient to irradiate the cell from the backside with a proton energy dependent of the glass thickness. The method is applied to predict the electrical degradation of a silicon solar cell at the end of its life in a low altitude orbit and to estimate the damage produced as consequence of the October 19, 1989 solar proton event. The results obtained are compared with predictions of the U.S. Jet Propulsion Laboratory method.

Anomalous degradation in silicon solar cells subjected to high-fluence proton and electron irradiations

Distinct from the well-known logarithmic degradation in electrical performances of a crystalline silicon solar cell, an anomalous degradation of short-circuit current density (Isc) was observed in a cell irradiated by energetic protons and electrons at high fluence. From results of proton irradiations with various energies (0.4–10 MeV) and high frequency (1 MHz) capacitance measurements, the anomalous drop of Isc is found to be caused by (1) the p-type substrate changes into the intrinsiclike layer (Fermi level shift) by the irradiations, followed by an extension of the depletion layer, and (2) the drift length of the minority carrier becomes shorter than the depletion layer.

Mechanism of anomalous degradation of silicon solar cells subjected to high-fluence irradiation

We have found anomalous degradation of electrical performance in silicon solar cells designed for space use due to high-fluence irradiation of charged particles, e.g., 1 MeV-electrons of /spl sim/10/sup 17/ e/cm/sup 2/ and 10 MeV-protons of /spl sim/10/sup 14/ p/cm/sup 2/. This anomalous degradation has two typical features, i.e., sudden-drop-down of electrical performances and slight recovery of the short circuit current I/sub SC/ just before the sudden-drop-down, which cannot be explained by a conventional model based on decrease of the minority-carrier life-time. In order to account for these features, we propose a new model, in which decreases of the majority-carrier concentration and the minority-carrier mobility are considered in addition to that of the minority-carrier life-time. The anomalous degradation observed is well represented by this model.