Solar cell degradation : the role of moisture ingress

Moisture ingress is one of the key fault mechanisms responsible for photovoltaic (PV) devices degradation. Moisture and moisture induced degradation (MID) products can attack the solar cell and the PV module components which can lead to solar cell degradation (e.g., microcracks), corrosion, optical degradation, potential induced degradation (PID), etc. These MID mechanisms have dire implications for the performance reliability of PV modules. Understanding the influence of moisture ingress on solar PV device’s degradation will boost the interest in investing in solar PV power installations globally, especially in the Nordics. In this thesis, the effect of moisture ingress on 20-years old field-aged multicrystalline silicon (mc-Si) PV modules is investigated. The defective areas in the PV modules were identified using visual inspection, electroluminescence (EL), ultraviolet fluorescence (UV-F), and infrared thermal (IR-T) techniques. Scanning electron microscopy and energy dispersive Xray spectroscopy (SEM-EDS) analyses were used to elucidate the role of moisture on the observed degradation mechanisms. In addition, temperature coefficient profiling is used as a diagnostic tool to characterize different moisture induced defects. The ethylene vinyl acetate (EVA) front encapsulation was found to undergo optical degradation and the extracted cells show dark discolored Tedlar®/Polyester/Tedlar® (TPT) backsheets. Corrosion at the solder joint was dominant and is attributed to the dissolution of lead and tin (main components of solder) and the Ag grids in moisture and acetic acid due to galvanic corrosion. Degradation of the EVA encapsulation produces acetic acid, carbon dioxide, phosphorus, sulfur, fluorine, and chlorine. It was observed that under the influence of moisture ingress, leached metal ions e.g., Na, Ag, Pb, Sn, Cu, Zn, and Al migrate to the surface of the solar cells. This led to the formation of oxides, hydroxides, sulfides, phosphates, acetates, and carbonates of silver, lead, tin, copper, zinc, and aluminum. Also, other competing reactions led to the formation of stannates of copper, silver, sodium, and zinc. Similarly, migration of silver and aluminum to the surfaces of the TiO2 antireflection coating (ARC) nanoparticles (NPs) lead to the formation of titania-alumina and silver-titania complexes. Formation of these titania-metal complexes affects the opto-electrical efficiency of the TiO2 ARC in the PV module. Additionally, in the presence of moisture and acetic acid, Pb is preferentially corroded (to form lead acetate complexes) instead of the expected sacrificial Sn in the solder. In the EL and UV-F images, these degradation species appear as dark spots, and as hot spots in IR-T images. More importantly, these MID defects and fault modes lead to parasitic resistance and mismatch losses, and hence, degradation in the current-voltage (I-V) characteristics, temperature coefficients, and maximum power (Pmax) of the field-aged PV modules. The observed temperature sensitivities are characteristic of different moisture-induced defects. Taken together, this work has expounded on the understanding and detection of MID phenomenon in field-deployed solar PV modules.publishedVersio

Delamination-and electromigration-related failures in solar panels—a review

The reliability of photovoltaic (PV) modules operating under various weather conditions attracts the manufacturer’s concern since several studies reveal a degradation rate higher than 0.8% per year for the silicon-based technology and reached up to 2.76% per year in a harsh climate. The lifetime of the PV modules is decreased because of numerous degradation modes. Electromigration and delamination are two failure modes that play a significant role in PV modules’ output power losses. The correlations of these two phenomena are not sufficiently explained and understood like other failures such as corrosion and potential-induced degradation. Therefore, in this review, we attempt to elaborate on the correlation and the influence of delamination and electromigration on PV module components such as metallization and organic materials to ensure the reliability of the PV modules. Moreover, the effects, causes, and the sites that tend to face these failures, particularly the silicon solar cells, are explained in detail. Elsewhere, the factors of aging vary as the temperature and humidity change from one country to another. Hence, accelerated tests and the standards used to perform the aging test for PV modules have been covered in this review

Photovoltaic Module Reliability Workshop 2010: February 18-19, 2010

NREL's Photovoltaic (PV) Module Reliability Workshop (PVMRW) brings together PV reliability experts to share information, leading to the improvement of PV module reliability. Such improvement reduces the cost of solar electricity and promotes investor confidence in the technology--both critical goals for moving PV technologies deeper into the electricity marketplace

Long-Term Durability of Rooftop Grid-Connected Solar Photovoltaic Systems

Compared to their initial performance, solar photovoltaic (PV) arrays show long-term performance degradation, resulting in lower like-for-like efficiencies and performance ratios. The long-term durability of polycrystalline silicon (p-Si) solar PV modules in three roof-top grid-connected arrays has been examined. Electrical output, ambient temperature, cell temperature, solar irradiance, solar irradiation, and wind speed data were collected at hourly intervals from 2017 to 2021 from three 50 kWp PV installations in Northern Ireland. The results show the extent to which higher PV temperatures associated with more intense solar radiation decrease efficiency, fill factor and maximum power output for PV arrays in a temperate climate. Long-term durability trends for grid-connected roof-top solar photovoltaic systems can be obscured by diurnal and seasonal changes in environmental conditions. To reduce the influence of variable conditions, performance ratios (PRcorr) were “corrected” using the measured annual average cell temperature (Tcell_avg). Introduction of this temperature-correction reduced the seasonal variation of the performance ratio. Using temperature-corrected performance ratios, long-term (in this case those seen after fiveyears operation) performance degradation trends become evident with high confidence after six months for one PV array and within three years for the two other arrays. If lower statistical confidence in trends is acceptable, long-term degradation rates can be identified within one year of operation for all PV arrays examined. These results have the important implication that relatively short-duration outdoor PV performance monitoring may be reliably used to estimate long-term degradation and/or to calibrate normally-conducted accelerated testing

Modeling and Optimization of Renewable Energy Systems

This book includes solar energy, wind energy, hybrid systems, biofuels, energy management and efficiency, optimization of renewable energy systems and much more. Subsequently, the book presents the physical and technical principles of promising ways of utilizing renewable energies. The authors provide the important data and parameter sets for the major possibilities of renewable energies utilization which allow an economic and environmental assessment. Such an assessment enables us to judge the chances and limits of the multiple options utilizing renewable energy sources. It will provide useful insights in the modeling and optimization of different renewable systems. The primary target audience for the book includes students, researchers, and people working on renewable energy systems

Grain boundaries in polycrystalline materials for energy applications: First principles modeling and electron microscopy

\ua9 2024 Author(s). Polycrystalline materials are ubiquitous in technology, and grain boundaries have long been known to affect materials properties and performance. First principles materials modeling and electron microscopy methods are powerful and highly complementary for investigating the atomic scale structure and properties of grain boundaries. In this review, we provide an introduction to key concepts and approaches for investigating grain boundaries using these methods. We also provide a number of case studies providing examples of their application to understand the impact of grain boundaries for a range of energy materials. Most of the materials presented are of interest for photovoltaic and photoelectrochemical applications and so we include a more in depth discussion of how modeling and electron microscopy can be employed to understand the impact of grain boundaries on the behavior of photoexcited electrons and holes (including carrier transport and recombination). However, we also include discussion of materials relevant to rechargeable batteries as another important class of materials for energy applications. We conclude the review with a discussion of outstanding challenges in the field and the exciting prospects for progress in the coming years

Indium-free transparent conductive oxides for improved solar cell performance and reliability

The rising adoption of solar cells worldwide necessitates reducing solar cell costs, enhancing cell efficiency, and long-term module reliability. New solar cell architectures such as silicon heterojunction (HJT) and thin-film technology like an organic solar cell, perovskite, III-V, copper indium gallium selenide (CIGS), etc. are actively being investigated. The majority of them implement a transparent conductive oxide (TCO), predominantly indium tin oxide (ITO), in their device structure. With the rising cost and depleting indium reserves, it is essential to find alternatives. This thesis focuses on developing and analysing indium-free TCOs fabricated using atomic layer deposition (ALD) and explores various applications of TCOs for solar cells. It begins with a detailed examination of the evolving relevant literature, followed by a detailed description of the techniques used throughout the thesis. ALD grown ZnO based TCO is studied. Firstly, a DFT analysis of various dopants of ZnO is presented. Subsequently, Zr doped ZnO is fabricated, characterized, and implemented as an electron selective layer for organic photovoltaic cells (OPV). The introduction of Zr as a dopant increased electron mobility and a reduction of sheet resistance. This was translated into an OPV device which demonstrated an increase in 1% abs efficiency due to increased carrier collection. Graphene is a promising TCO due to its high conductivity and transparency. Unfortunately, the transfer process hinders its implementation in a solar cell as a top or bottom contact. In this work, the first transfer-free method was developed by growing graphene directly onto an ALD-grown functional layer (NiOx). It will be shown that the NiOx layer gets partially reduced to Ni by carbon, which subsequently catalysis the graphene growth. Potential induced degradation (PID) has once again become a major reliability issue for solar manufacturers. But the determination and identification of PID before module fabrication is still a challenge. This work presents a novel method to provide accelerated lamination free PID testing at a solar cell level. This method was validated by implementing it on cells from different manufacturers. In addition, this novel method was used to test the effectiveness of ALD films, mainly ZnO and Al-doped ZnO (AZO), to prevent PID at a solar cell device level. It will be shown that the addition of a 5 nm TCO thin film can prevent the Na diffusion into the solar cell, thus protecting the cell from PID. Finally, the techno-economic analysis of ALD TCOs for solar cells is presented. It was shown that with the current tools in the market and indium costs, ALD based TCOs are an economical alternative. Furthermore, a Levelized costs of electricity (LCOE) study on the ALD capping layer demonstrated a >1% improvement in LCOE, suggesting that PID prevention using ALD capping layer is technologically and economically advantageous

Investigation of potential induced degradation as a performance limiting defect in photovoltaic modules

Potential Induced Degradation (PID) impacts negatively on photovoltaic (PV) module durability because it significantly affects the output of PV modules and systems. Unless detected at infancy, PID progression can be catastrophic. This study involved systematic PID stressing of PV modules using a custom-built environmental chamber that can achieve suitable environmental conditions, viz., of the 35 °C ± 1 °C and relative humidity of 75 % ± 5 %. The first part of this work was to induce PID using three approaches: climate chamber testing, inducing PID using a conductive aluminium plate on the surface of the module without touching the frame and a localised PID induction on one cell in a module. The second part is to detect induced PID using Electroluminescence (EL) images taken at current corresponding to 10% Isc, EL histograms analysis and Voc ratio taken at 1000 W/m2 to 200 W/m2 . The third part is to study module regeneration after PID shunting degradation in two ways, viz., forced reverse polarization and natural recovery. The PID detection tools used in this work are well known module characterization techniques such as EL imaging, Infrared imaging, and light and dark current-voltage measurements. These characterisation tools are used in combination to detect defects such as optical losses, cracks, breakage, electric circuit degradation and PID. Under normal testing PID was detected and in some cases, modules were able to recover, while for advanced stage PID regeneration or PID reversal was difficult. This thesis focuses on PID detection at infancy using three approaches; EL imaging at current corresponding to 10% of Isc. Light and dark current – voltage measurements (L-IV & D-IV) and open circuit voltage (Voc) ratios at low irradiance. The early detection procedures are essential in reversing the degradation caused by PID which is reversible. The time taken to reverse the PID degradation will depend on the extent of the degradation. If detected early, it will take a short period of time to completely reverse lost power. Infrared thermography is a non-contact characteristic tool that can be deployed in large scale plants using drones to detect the presence of PID in PV plants. Module performance and device parameters extracted from the L-IV curves on a module before and after PID stress, such as Pmpp, Voc, Isc Fill Factor (FF), shunt resistance (Rsh) and series resistance (Rs) and ideality (n) are sensitive to PID shunting. Voc and Rsh drop significantly with the onset of PID, while Rs increases. The decrease in Voc and Rsh is due to heavy shunting on the module resulting in increased carrier recombination, while the increase in Rs is due to increased shunting paths leading to decreased photocurrent. When substantial degradation on a module occurs Pmpp, FF and n will drop and at very advanced stage of PID degradation Isc may drop excessively

The Electronic Properties of Defects in Silicon Solar Cells

This thesis is concerned with the measurements and interpretation of the electronic properties of defects in high-efficiency silicon solar cells. In Photovoltaic community, defects in crystalline silicon wafers or introduced during the solar cell fabrication can limit the performance and stability of the final devices. These defects are traditionally and widely studied using lifetime spectroscopy such as quasi-steady-state photoconductance decay measurements, in combination with Shockley-Read-Hall model to extract energy levels and capture cross section ratios of recombination active centres. In this thesis, the junction spectroscopy deep level transient spectroscopy is used for further understanding of the electronic properties of defects in silicon solar cells, with direct measurements of activation energy levels and majority carrier capture cross sections. As a result, insights of the defect formation/ dissociation mechanisms are provided and the physics features of the traps in silicon materials are understood for solar cell defect engineering to potentially achieve higher efficiency

LSSA (low-cost Silicon Solar Array) project

Work performed in the field of photovoltaic research by the low cost silicon solar array project of jet propulsion laboratory was described. Background technical information was also furnished