CIGS Modules Research Articles

CIGS박막전지를 이용한 컬러BIPV 디자인 현황 및 사례고찰

This study examines the development status of domestic color solar cells and eight domestic and international application sites to overcome the limitations of early-stage BIPV modules that focus only on expanding and distributing power generation and do not meet various building regulations and rules, and to solve somewhat neglected building and cityscape problems. In addition, it analyzes its characteristics to improve the misconceptions and limitations of existing BIPV and to contribute to improving domestic architectural application conditions and future energy policies by reborn as a true product with the function of building exterior materials. In this study, it was found through domestic and international cases that the common feature of BIPV installation cases using CIGS thin-film cells is that BIPV is installed on the entire exterior of a building to meet power generation while pursuing consistency in the design of the exterior, and that CIGS modules satisfy most of the architectural functions that BIPV should have. In addition, although the inevitable efficiency reduction occurs when PV modules have color, it was confirmed that this is a part that must be tolerated to some extent in the comprehensive and combined sense that the ultimate goal of BIPV is to realize sustainable architecture by replacing existing building materials while generating energy. However, there are still many shortcomings in satisfying the color and size required in architecture, and the color that takes into account regional characteristics, so further technological development and advancement are needed.

3-D curved composite façade elements with PV: Results of a pilot project

This paper describes the design, manufacturing, installation and monitoring of a BIPV system that consists of coloured 3D structured façade elements, mounted on an existing office building at the High Tech Campus in Eindhoven. The façade elements contain thin film CIGS modules, which adopt the curved structure of the elements. The encapsulation of the PV modules into the façade elements, the colouration and the curvature led to a relative loss of about 10 % of the efficiency. The PV façade consists of 48 elements with a STC capacity of 5.8 kWp. Each element was equipped with a power optimizer, enabling individual monitoring of each façade element. The elements have been installed at the east and south façade of the building. The monitoring presented in this paper comprised a period of 5 months: the summer and autumn of 2023. The DC performance ratio during that period was 75 % for the elements on the East façade and 80 % for the elements on the South façade; which is in accordance with simplified model predictions. The result is a visual attractive retrofitted PV façade contributing to zero emission strategy of the Eindhoven High Tech Campus.

Light induced degradation of CIGS solar cells

Considering warranted lifetimes of PV modules of typically 20-30 years, the performance stability of PV modules is one of the most crucial factors regarding power generation and yield. Long term outdoor performance studies depict realistic operation conditions best, but the correlated nature of e.g. irradiance and temperature impedes the physical interpretation. The possibility to control and tune the conditions in laboratory experiments enables to decompose effects, that are typically overlayed in outdoor experiments. This way, laboratory are crucial to interpret the results obtained in outdoor degradation studies. One driving force of degradation of CIGS modules is light exposure. In literature the focus of light induced degradation (LID) of CIGS modules and solar cells is on metastable changes analyzed on time scales ranging from minutes to hours. In this work we expose industrially produced encapsulated CIGS solar cells for more than 1000 h to light with varied intensity under varied temperature conditions. Such, we aim to study temperature and light intensity dependencies of the observed performance changes. Furthermore, we study the influence of applied bias by comparing LID at short and open circuit. We demonstrate that LID under short circuit conditions leads to VOC degradation, while being temperature assisted and not dependent on the irradiance intensity. CIGS solar cells kept at open circuit conditions appear to be stable under illumination. Exploiting the one diode model, we further connect the observed temperature assisted performance loss to enhanced recombination with lower ideality factor, in comparison to the dominant recombination process before degradation.

Insights into the moisture‐induced degradation mechanisms on field‐deployed CIGS modules

AbstractMoisture ingress is known to be one of the most frequent and detrimental causes of photovoltaic (PV) modules degradation. In an original approach, the present work applies the full analytic capability of lab‐scale equipment to characterize a commercial Cu(In,Ga)(Se,S)2 (CIGS) module that degraded in the field due to moisture ingress. By extracting (coring) and unpackaging samples from different areas of the module, we are able to track the propagation of the degradation mechanisms with respect to both material and electrical properties. The three following locations in the device were found to be affected by the water ingress: first, the encapsulant, ethylene‐vinyl acetate (EVA), resulting in delamination and acetic acid formation; second, the molybdenum (Mo) back contact, which oxidizes and corrodes entirely at the P3 scribes; lastly, the ZnO front contact, through the formation of Zn‐based hydroxides and its further reaction with the Mo migrating from the degraded scribes. The main impact on the electrical properties is an increase in series resistance and a decrease in both open‐circuit voltage and short‐circuit current. In the last degradation stage, that is, the most degraded area of the module, a complete performance loss is observed. The results of this work further our understanding of the physics and chemistry involved in the moisture‐induced degradation in CIGS modules. In particular, the study highlights the interactions between the various degradation products and associated degradation mechanisms. These results also illustrate the broader potential of the coring and unpackaging method for reliability studies of full‐sized, field‐degraded commercial PV modules.

Extraction and microscopic analysis of partial shading‐induced defects in a commercial CIGS PV module

AbstractThe ever‐increasing instalment capacity of Cu (In, Ga)(Se, S)2‐based photovoltaics calls for a better understanding and control of their reliability. In this paper, we show how using a coring‐based method, small samples can be extracted from full size commercial modules, and prepared for lab‐scale analysis. The method is applied to a Cu (In, Ga)(Se, S)2 (CIGS) module where a non‐reversible, propagating (‘wormlike’) defect has been created in a controlled partial shading experiment. Through current–voltage, photoluminescence and illuminated lock‐in thermography analyses on an undamaged part of the module, the method used is shown to yield fully functional, undamaged active cells, with a photovoltaic conversion efficiency above the full module efficiency. Where the wormlike defects were present, a typical strong shunting behaviour is observed, as well as an increased sulphur content near the edge of the wormtrails. Furthermore, the wormlike defect propagation is shown to be strongly influenced by the present of specific features near the interconnects, which could be the result of manufacturing. These results demonstrate the potential of coring to analyse module failure with all the laboratory tools available. They also shed some light on how wormlike defects, which are a rare but serious hazard for CIGS modules reliability, can form and propagate in commercial, monolithically interconnected modules.

Prediction Model for the Performance of Different PV Modules Using Artificial Neural Networks

This study presents a prediction model for comparing the performance of six different photovoltaic (PV) modules using artificial neural networks (ANNs), with simple inputs for the model. Cell temperature (Tc), irradiance, fill factor (FF), short circuit current (Isc), open-circuit voltage (Voc), maximum power (Pm), and the product of Voc and Isc are the inputs of the neural networks’ processes. A Prova 1011 solar system analyzer was used to extract the datasets of IV curves for six different PV modules under test conditions. As for the result, the highest FF was the mono-crystalline with an average of 0.737, while the lowest was the CIGS module with an average of 0.66. As for efficiency, the most efficient was the mono-crystalline module with an average of 10.32%, while the least was the thin-film module with an average of 7.65%. It is noted that the thin-film and flexible mono-modules have similar performances. The results from the proposed model give a clear idea about the best and worst performances of the PV modules under test conditions. Comparing the prediction process with the real dataset for the PV modules, the prediction accuracy for the model has a mean absolute percentage error (MAPE) of 0.874%, with an average root mean square error (RMSE) and mean absolute deviation (MAD) of, respectively, 0.0638 A and 0.237 A. The accuracy of the proposed model proved its efficiency for predicting the performance of the six PV modules.

Out-door reliability and degradation of HIT, CIGS, n-type multi-busbar, PERC, and CdTe modules in Shanghai, China

As the installation of PV power grid increases, it becomes vital to know the out-door reliability and degradation of the modules. In this study, more than 30 kW modules have been installed in Chinese Academy of Sciences-Shanghai Institute of Microsystem & Information Technology (SIMIT). The outdoor performance of seven different PV modules, i. e. HIT, CIGS, n-type multi-busbar module, PERC, and CdTe were measured from 2016 to 2018. The performance of all of the seven kinds of PV modules is excellent in March, April and May of 2018, owing to the relative low temperature and the intense irradiance. The daily and monthly PR of the PV modules displays distinct seasonal cyclic patterns. The PR calibrated to 25 °C (PRT = 25°C) is more consistent than the uncalibrated PR throughout the whole year. The comparison of the annual average uncalibrated PR is: bifacial HIT (1.0345)＞CIGS (1.0258)＞n-type multi-busbar module (0.9656)＞monofacial HIT (0.9648)＞sc-Si PERC (0.9591)＞mc-Si PERC (0.9346)＞CdTe (0.9067). Moreover, the power degradation after the installation more than 2 years is: mc-Si PERC (5.33%)＞n-type multi-busbar module (3.19%)＞sc-Si PERC (1.32%)＞monofacial HIT (0.25%). The property improvement of monofacial HIT and bifacial HIT after the light soaking was observed and the power increase of bifacial HIT is 0.72% in these two years, owing to the metastability of the amorphous—crystalline silicon heterointerface after the light soaking.

Study of the second-generation of CdTe and CIGS thin film PV modules under natural sunlight conditions

There is a significant amount of research in the literature concerning the performance of solar panels operating during outdoor exposure, but the full topic is not yet exhausted. One of the reasons is that the photovoltaic cell technology is constantly evolving. In this paper, a comparison of two types of CdTe and CIGS modules operated with a nominal power of 80 W and 140 W, respectively is studied. The module tests were performed under external conditions during autumn, winter, spring, and summer from October 2019 to July 2020 in the temperate climate of Miękinia, South Poland. The photovoltaic panels were connected to the electric grid via microinverters. During the tests, the temperature of the panels was monitored. To determine the influence of solar radiation on the energy conversion efficiency of photovoltaic panels, a pyranometer installed in the plane of the panels was used. Based on the monitoring of the atmospheric conditions and the measurement of instantaneous power, the efficiency of the modules is determined.

Unraveling the cause of degradation in Cu(In,Ga)Se2 photovoltaics under potential induced degradation

AbstractCopper indium gallium diselenide (CIGS) based technology is actively competing in the global photovoltaic market with high conversion efficiency. Commercial CIGS modules are anticipated to perform on rated output in the field condition for 20 years. Potential induced degradation (PID) is considered as one of the critical concerns among all the current reliability assessment issues. PID accelerated tests have been performed on pre‐commercial CIGS modules to investigate reduction in electrical performance. We report the severe reduction in electrical performance after PID is correlated to the microstructural and chemical properties of the constituent materials. Under extreme PID stress, the cell surface reveals various defects including crater formation. The aim of this article is to explore the consequences of PID induced craters on the efficiency of CIGS solar cells by investigating material degradation kinetics. In this perspective, we present the root cause of PID in CIGS thin‐film modules in relation to microstructural defects by detailed investigation using J‐V analysis, field emission scanning electron microscope (FESEM), Raman spectroscopy, X‐Ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). This analysis can provide more effective and sustainable research strategies to cultivate more efficient and reliable CIGS technologies in the long run.

Empirical Models Applied to Distributed Energy Resources—An Analysis in the Light of Regulatory Aspects

According to the International Electrotechnical Commission (IEC) 61853 standard, the power rating of photovoltaic (PV) modules must be done on a measurement matrix that broadly covers the ranges of operating conditions encountered in the field. These results are becoming more frequent in recent module datasheets. This paper investigates the effectiveness of applying existing empirical PV performance models while using a matrix with 18 operational records, similar to the 22 that were recommended by IEC 61853, as an alternative to the thousands of records that are conventionally used to determine their coefficients. A review of fifteen empirical models is presented and the procedures for determining their coefficients are discussed. In order to validate them, they were applied to data from fourteen PV modules, which remained installed outdoors for about one year, in three locations with distinct climate types. Although the uncertainties that were obtained with the proposed approach, as compared to the conventional one, are about 1% higher for xSi and CdTe modules, and somewhat higher for mSi and CIGS modules, the total uncertainties were only around 5%, a value that is quite adequate for evaluating module performance. Moreover, these uncertainties were from two to five times smaller than those that were obtained by the method that was recommended by IEC 61853 for this purpose.

A non-vacuum dip coated SiO2 interface layer for fabricating CIGS solar cells on stainless steel foil substrates

A novel solution processed SiO2 coating is investigated for use as an interface layer between the substrate and Mo back contact for making CIGS solar cells on flexible SS foils. Prior to deposition of Mo, a ~ 1 μm thick SiO2 layer is applied on commercially available SS foils using an economical non-vacuum dip coating method. CIGS absorbers as well as complete CIGS solar cells having the structure Mo/CIGS/CdS/i-ZnO/AZO are grown on SS foils with and without the interface layer and their characteristics are compared. The interface layer improves the adhesion and high temperature mechanical stability of Mo back contact. Although phase formation of CIGS absorber is not influenced by the presence of interface layer, the grain structure and surface morphology are positively impacted, resulting in an enhanced solar cell performance. Composition measurements did not reveal any increase of Fe content in the CIGS absorber after the high temperature selenization step. However, the role of interface layer in blocking the diffusion of Fe from the SS substrate is uncertain, as the high-quality Mo back contact itself could be acting as an efficient Fe barrier layer. The interface layer is capable of electrically isolating Mo back contact from the underlying SS substrate, thus offering the prospect of monolithic integration for making lightweight CIGS modules. With a simple and inexpensive deposition process, which can be easily upscaled for large substrates, the dip-coated SiO2 interface layer could be a suitable alternative for various existing vacuum deposited layers in realizing low-cost flexible CIGS modules.

Assessment of spectral effects on outdoor characterization of PV modules using silicon reference cells with spectral filters

This article describes outdoor temperature-controlled measurement of various photovoltaic (PV) modules fabricated using different technologies and using reference cells with spectral filters. Short-circuit current measurements of all PV modules and reference cells were recorded simultaneously using 16-bits Keysight digitizers and high-resolution Agilent multimeters. The spectral incompatibility factor was calculated considering the spectral response of each device and the spectrum measured outdoors. Corresponding spectra were also generated by the simple model of atmospheric radiative transfer of the sun SMARTS2 and were additionally used to compare the spectral incompatibility factors. The validation of the measurement method was demonstrated by comparing the incompatibility factor calculated with variation of the short-circuit current relationship between the device under test and the reference cell over time. Additionally, it was evaluated how the relationship between spectral variation of irradiance and the spectral response of different technologies affects the productivity in thin-film modules. Main observation from measurements (performed in Labsol) was that a-Si/μ-Si, CdTe, and triple a-Si junction converted 0.21%, 2.47%, and 3.65% more irradiation into electric current (in summer), respectively, compared to c-Si technology. The PV CIGS module converted on average 0.26% more irradiation into electric current in winter compared to c-Si technology. The results help to understand the spectral effects on the working of outdoor PV module and the relationships between measured and modeled spectra, as well as errors introduced by the spectral incompatibility factor.

Macroscopic Nonuniformities in Metal Grids Formed by Cracked Film Lithography Result in 19.3% Efficient Solar Cells

Cracked film lithography (CFL) is an emerging method for patterning transparent conductive metal grids. CFL can be vacuum- and Ag-free, and it forms more durable grids than nanowire approaches. In spite of CFL's promising transmittance/grid sheet resistance/wire spacing tradeoffs, previous solar cell demonstrations have had relatively low performance. This work introduces macroscopic nonuniformities in the grids to improve the short-circuit current density/fill factor tradeoff in small area Cu(In,Ga)Se2 cells. The performance of optimized baseline grids is matched by CFL grids with microscopic openings and macroscopic patterns, culminating in a 19.3%-efficient cell. Simulations show that uniform CFL grids are enhanced by patterning because it leads to better balance among shadowing, grid resistance and transparent conductive oxide resistance losses. Thin-film module efficiency calculations are performed to highlight the performance gains that metal grids can enable by eliminating the transparent conductive oxide losses and widening monoliths. Adding the patterned CFL grids demonstrated in this work to CIGS modules is predicted to reach 0.7% higher efficiency (absolute) than screen-printed grids.

Damage-free patterning of thermally sensitive CIGS thin-film solar cells: Can nanosecond pulses outperform ultrashort laser pulses?

Nanosecond pulses are usually not considered as a suitable candidate for low-damage processing of heat-sensitive materials due to high thermal effects and significant melt formation. Many studies have shown, that CIGS is thermally sensitive material and ultrashort lasers have been chosen as the primary source for the processing of CIGS cells. However, we report on the P3 scribing of CIGS thin-film solar cells with the ns pulse duration at the wavelength of 2.5 µm – a wavelength close to the mid-infrared region and compare the results with the ps pulses covering traditional wavelengths of 355 nm, 532 nm, 1064 nm, and 1342 nm. In our case, 6 ns pulses at 2.5 µm wavelength outperformed the picosecond laser sources operating at VIS and NIR wavelength range. The minimal P3 scribe conductivity of 4.7 mS/m was achieved for ns laser patterning, corresponding to simulated CIGS module efficiency loss of just 0.01%. We proposed that high absorption in the transparent conductive oxide - TCO efficiently shielded the underlying CIGS with only a fraction of energy reaching the back-contact. Finally, results show that nanosecond pulses can be as competitive as picosecond ones for P3 processing of high-efficiency CIGS devices.

Analysis of moisture-induced degradation of thin-film photovoltaic module

To enhance the reliability of the thin-film solar cell technologies, it is required to analyze and understand the moisture-induced degradation. In this study, the moisture induced degradation of glass-to-glass CIGS module are comprehensively analyzed. CIGS modules are fabricated and tested under damp-heat conditions with periodical measurement of the electrical characteristics. Individual layers of the module are also investigated experimentally and the moisture induced degradation is discussed. A modified method to extract the diode model parameters from degraded I–V curves is proposed and applied to the degraded data. Finally, the degradation rates are modelled and the effect of model parameters degradation on the power of module are quantitatively compared. It suggests that the power degradation of CIGS module under the damp-heat environment is more affected by the enhanced recombination of the absorber layer than the degradation of the metal layer or the leakage over layers.

Enhancing passive radiative cooling properties of flexible CIGS solar cells for space applications using single layer silicon oxycarbonitride films

Satellites in lower earth orbits have been primarily powered by photovoltaic modules. With growing power demand for new satellite concepts, solar cells are required to be flexible and ultra-lightweight to decrease launch costs. CIGS thin film solar technology is a promising candidate, since it can be manufactured on flexible substrates and possesses high radiation hardness. Poor radiative properties of CIGS on the other hand, lead to high temperatures and therefore power loss. High emissivity coatings on CIGS have already been reported but the influence on thermal and electrical aspects have not been addressed. Here we present the optical properties of silicon-oxycarbonitride coatings and their effect on electrical parameters on CIGS cells to be used for the DLR's GoSolAr power sail mission. We show that the single layer coating can significantly increase emissivity from 0.3 to 0.72, with minimal spectral losses and negligible impact on the functioning of the underlying CIGS cell. We simulated the thermal impact of the coating on solar cells in orbit and can predict that the maximum temperature of the cells is reduced by 30 °C, resulting in a significant power gain. Additionally, the coating has an emissivity of 0.87 in the atmospheric window of 8–13 μm making it a very good passive radiative cooler for terrestrial solar cells. The low-cost coating can replace glass and the process can be scaled up for large CIGS modules. The coating can also significantly increase the power to mass ratio of solar modules, reducing costs for space applications.

How the absorber thickness influences the formation of reverse bias induced defects in CIGS solar cells

When a PV module is partially shaded, the shaded solar cells operate in a reverse bias condition. For Cu(In,Ga)Se2 cells this condition can cause defects that irreversibly reduce the output of these cells and the full module. In order to design robust shade-tolerant CIGS modules details need to be known of the conditions at which these defects will be formed. In this study a large number of cells were exposed to different reverse bias conditions. By using simple statistics the probability of the occurrence of defects as a result of reverse bias at any given voltage has been determined. Based on our experiments we have found that the absorber thickness is one of the main parameters that affects the shade-tolerance: the thicker the absorber, the more shade tolerant the CIGS module will be.

Reliability implications of partial shading on CIGS photovoltaic devices: A literature review

Abstract

An accurate one-diode model suited to represent the current-voltage characteristics of crystalline and thin-film photovoltaic modules

In this paper a new one-diode model, conceived in order to be used to represent the current-voltage curves of both crystalline and thin-film photovoltaic modules, is presented. The model parameters are calculated from the information contained in the datasheets issued by manufactures by means of simple iterative procedures that do not require the assumption of simplifying hypotheses. Some innovative relations describing the dependence of the parameters from the solar irradiance and cell temperature are adopted in order to permit the model to reliably simulate the electrical behaviour of photovoltaic devices operating in real conditions.The ability of the model to calculate the current-voltage characteristics issued by manufacturers for values of the solar irradiance and cell temperature also far from the standard rating conditions was verified for various photovoltaic technologies, such as monocrystalline, polycrystalline, amorphous silicon, CIS, CIGS and tandem junction photovoltaic modules. The percentage ratio of the mean absolute difference of current to the rated current at the maximum power point ranges from 0.071% to 1.807%; the analogous ratio of power varies between 0.056% and 1.720%. A comparison with the results obtained with other recognised two-diode models is also presented.

High-resolution, parametric BIPV and electrical systems modeling and design

The design of building integrated photovoltaics (BIPV) often involves complex geometries, non-uniform irradiance conditions and partial shading. This can lead to high energy losses if not considered adequately. This paper presents a BIPV modeling and optimization method which uses a parametric 3D modeling tool, coupled to a high-resolution ray-tracing irradiance simulation and an electrical model based on the single diode model on a subcell level. With the use of a genetic algorithm, electrical interconnections of the modules are optimized for maximum yield. The presented approach allows the simulation and optimization of BIPV in urban environments where complex shading occurs and high electrical mismatch of photovoltaic cells and modules is to be expected. It allows specific geometric design and optimization of photovoltaic installations and their electrical layout. The electrical simulation is validated for both flat and curved thin-film CIGS modules, as well as for two connected thin-film CIGS modules under deferring irradiance and partial shading conditions. The presented method is further applied in a case study on a double-curved roof shell. The results show that by using genetic algorithms the layout can be optimized to minimize the string mismatch losses for BIPV networks with a variety of modules. The detailed electrical simulation allows to quantify effects of module designs and inverter concepts on the system performance. This is demonstrated for the case study, indicating that thin-film modules with longitudinal cell direction outperform modules with orthogonal cell direction by up to 8%. Furthermore, module-integrated bypass diodes show little benefits for the best performing module technologies. Post-processing the results allows the evaluation of annual, seasonal, daily and hourly losses on a highly disaggregated level.