Thin-film Modules Research Articles

Double Green Process: a low environmental impact method for recycling of CdTe, a-Si and CIS/CIGS thin-film photovoltaic modules

On the basis of the method for managing the end of life of CdTe photovoltaic panels previously proposed by the authors, a new method for the recycling of all types of thin-film panels (CdTe, a-Si and CIS/CIGS) has been developed and optimised under a research project founded by Enel Foundation and CRUI Foundation. The DGP process has been developed through a feasibility study carried out from three points of view: technical, environmental and economic. The process is composed by two sub-processes matched to each other, one suitable for CdTe panels (named DGPa) and the other one for a-Si and CIS/CIGS panels (DGPb). The Double Green Panel process is based mainly on mechanical treatments with a minimum use of chemicals and it is characterised by a greater level of automation and a high flexibility in production capacity. The potential environmental impacts of various configurations of the DGP process have been extensively analysed with LCA tool in order to develop an environmentally friendly process. The economic feasibility has been assessed through the Discounted Cash Flow Analysis (DCFA) method. The revenues associated to the recovery of valuable and common materials and the recycling costs have been taken into account.

Mixed Valence Perovskite Cs2 Au2 I6 : A Potential Material for Thin-Film Pb-Free Photovoltaic Cells with Ultrahigh Efficiency.

New light is shed on the previously known perovskite material, Cs2 Au2 I6 , as a potential active material for high-efficiency thin-film Pb-free photovoltaic cells. First-principles calculations demonstrate that Cs2 Au2 I6 has an optimal band gap that is close to the Shockley-Queisser value. The band gap size is governed by intermediate band formation. Charge disproportionation on Au makes Cs2 Au2 I6 a double-perovskite material, although it is stoichiometrically a single perovskite. In contrast to most previously discussed double perovskites, Cs2 Au2 I6 has a direct-band-gap feature, and optical simulation predicts that a very thin layer of active material is sufficient to achieve a high photoconversion efficiency using a polycrystalline film layer. The already confirmed synthesizability of this material, coupled with the state-of-the-art multiscale simulations connecting from the material to the device, strongly suggests that Cs2 Au2 I6 will serve as the active material in highly efficient, nontoxic, and thin-film perovskite solar cells in the very near future.

Modelling of flexible thin-film modules for building and product integrated photovoltaics

In this work we present a simulation of performance of curved thin-film modules for building and product integrated photovoltaic applications. Flexibility of design and possibility of achieving irregular shapes is important feature in these markets. The photovoltaic module model presented in this work is based on a coupled two-step model. The first 1D model describes the technology and outputs device current density in dependence of voltage, temperature, illumination, etc. The second 3D model uses this data as one of its inputs, and describes size, shape and interconnection of the individual cells within the curved flexible module. In this way power production of such photovoltaic system can be assessed in reasonable time and computing resources. Two study cases are presented: a dome shaped solar street lamp and a conic shaped active rooftop shading for a skylight.

Experimental Studies of Fire from CIGS Thin Film Solar Module Back

With the building integrated photovoltaic commonly using in residential and commercial buildings, fire researches about this new renewable energy system are still insufficient. Electrical failure may bring local fever at the backside of the module. In order to investigate fire potential in this situation, bench-scale experiments based on the cone calorimeter are conducted with different external heat flux from 20 to 45kWm-2 at intervals of 5 kWm-2. This paper focuses on the thermal properties and combustion behaviors of copper–indium–gallium–diselenide (CIGS) thin-film solar module, and also discusses the gas toxicity.

Measurement-Based Modeling of a Semitransparent CdTe Thin-Film PV Module Based on a Custom Neural Network

Semitransparent photovoltaic (STPV) can be employed in a wide application range to provide sunlight permeability for supplying solar electrical energy with some shading, which is preferable in hot areas. To predict the output power and formulate the performance of this type of photovoltaic (PV) system, the proposed approach analyzes a Thin-Film solar cadmium telluride-type module and develops a custom neural network (CNN) for modeling its generated power expressed by its mathematical formula. Experiments for single and multilayer installation topologies are conducted for performance analysis. The coefficients of the model equation are investigated based on a set of power-current curves. The developed model adopts three factors: a minimum number of hidden neurons, the use of all measured data to train the network weights, and a linear output activation function to reduce the complexity of solving the network equations. The results specify the limit at which this type of PV starts generating power from the experimental measurements and the comparison with its equivalent normal PV module. The CNN-based STPV module is verified by comparing with the experimental measurements results, which shows a reasonable R-square, while its performance is evaluated on the silicon-based PV by comparing its behavior with the two-diode model PV in the MATLAB-based simulation.

Analysis of the impact of a flexible photovoltaic tile shape on its performance

This paper addresses the subject of the building integrated photovoltaics (BIPV). The flexible thin-film CIGS module has been subjected to testing in order to investigate its electrical parameters and the possibilities of adaptation to the building structure. During analysis of performance of the tested building in real conditions, particular attention has been paid to changes in its parameters depending on the inclination angle and the shape of its surface in relation to the incident solar radiation. Current-voltage characteristics and power curves in the selected configuration of module deflections have been analysed. Changing the module’s inclination angle from the optimal 40° to 0° (horizontal arrangement of the module on the ground) reduced the value of generated current (by approx. 26%), voltage increase (by approx. 4%) and output power reduction by approx. 25%. The module generated a lower power compared to the basic test due to the irradiation limit reaching its surface (decrease in the irradiance value of less than 60% from 800 to 330 W/m2). Bending the module at an angle 90° to the ground affected the large unevenness of solar radiation values reaching its surface and even greater losses of generated energy. The values of idle voltage, short-circuit current and voltage in MPP did not change much in relation to the base measurement, however, a large drop in the value of current in MPP was noted, which led to a significant reduction of output power. Thus, the need to strive for the most advantageous exposure of BIPV elements in relation to the sun was demonstrated and the losses on energy yields resulting from the integration of photovoltaic tiles into the body of the building have been estimated.

Addressing Hotspots in the Product Environmental Footprint of CdTe Photovoltaics

A pilot study within the European Commission's “Single Market for Green Products” initiative has been developing standardized methods for measuring, verifying, and communicating a product's environmental performance. These methods provide the basis for identifying and then addressing hotspots in the product environmental footprint of photovoltaics (PV). In the case of CdTe PV, hotspots related to electricity usage in manufacturing, glass content in PV modules, and metal content in modules and balance of systems can be addressed through technology innovation. Transitioning to a larger, lighter (per unit area), more efficient, and still recyclable version of current thin film modules is expected to reduce the product environmental footprint of CdTe PV to a factor of 3.5–4 below that of an average PV module as proposed in the European Commission pilot study.

Identification and analysis of partial shading breakdown sites in CuInxGa(1-x)Se2 modules

In this study, CuInxGa(1-x)Se2 (CIGS) mini-modules are stressed under reverse bias, resembling partial shading conditions, to predict and characterize where failures occur. Partial shading can cause permanent damage in the form of ‘wormlike’ defects on thin-film modules due to thermal runaway. This results in module-scale power losses. We have used dark lock-in thermography (DLIT) to spatially observe localized heating when reverse-bias breakdown occurs on various CIGS mini-modules. For better understanding of how and where these defects originated and propagated, we have developed techniques where the current is limited during reverse-bias stressing. This allows for DLIT-based detection and detailed studying of the region where breakdown is initiated before thermal runaway leads to permanent damage. Statistics of breakdown sites using current-limited conditions has allowed for reasonable identification of the as-grown defects where permanent breakdown will likely originate. Scanning electron microscope results and wormlike defect analysis show that breakdown originates in defects such as small pits, craters, or cracks in the CIGS layer, and the wormlike defects propagate near the top CIGS interface.

Polylol-solution synthesis of CuInSe2 nanoparticles ink for scalable solution-based thin film photovoltaic cells

ABSTRACTA fast and facile ambient pressure solution chemical process was applied to grow chalcopyrite CuInSe2 nanoparticles by using common and inexpensive polylol ethylene glycol(EG), diethylene glycol(DEG) and triethylene glycol(TEG) as solvent, copper(II) chloride, indium(III) chloride and selenium powder as precursors, hydrazine hydrate and ethylenediamine as reducing agent and polyvinylpyrrolidone as capping agent. The products synthesized were characterized by XRD, TEM, HRTEM, EDS and UV-vis measurements based on different solvents EG, DEG and TEG, refluxing temperature and time as well as PVP adding amounts. The well-dispersed and single-phase CuInSe2 nanoparticles synthesized with TEG solvent were used to prepare nanoparticles colloidal ink by ultrasonically dispersing in absolute alcohol solvent and then deposit CuInSe2 thin films by layer-by-layer dip-coating nanoparticles ink. The deposited thin films were annealed in Ar atmosphere at 550°C for 30 min. Photovoltaic test devices with Mo-coated glass/CuInSe2/CdS/i-ZnO/AZO configuration were fabricated using the ink-coated and annealed CuInSe2 light-absorbing thin films, and the corresponding I-V characteristics were evaluated.

Performance Analysis of Crystalline Silicon and CIGS Photovoltaic Modules in Outdoor Measurement

Abstract The outdoor measurements (during two months experiment) of photovoltaic silicon and CIGS modules as well as simulation of energy production during the period experiment are presented in this paper. This paper offer comparison of construction and electrical characteristics of multicrystalline silicon based modules and CIGS based modules. The measuring system for PV modules efficiency research is shown. The nominal power of installed modules is 250 W for m-Si and 280 W for CIGS modules. The energy production in outdoor conditions at direct current side and alternating current side of each photovoltaic panel was measured. Each PV panel was also equipped with temperature sensor for screening panel temperature. The photovoltaic panels were connected to the electrical network with micro inverters. To determine the influence of irradiance at sunshine on power conversion efficiency of PV panels, the pyranometer was installed in the plane of the modules. Measurement of the instantaneous power and irradiance gave the information about the efficiency of a particular photovoltaic panels. In the paper all data from research installation were analysed to present the influence of solar cell technology on the power conversion efficiency. The results of energy production show that m-Si module produced more energy from square meter (30.9 kWh/m2) than CIGS module (28.0 kWh/m2). Thin film module shows the higher production per kWp than multicrystalline module: 217.3 kWh/kWp for CIGS and 201.9 kWh/kWp for m-Si. The energy production simulation (made by PV SOL software and outdoor measurements test are in the good agreement. Temperature power coefficient for the CIGS module is twice lower than for the multicrystalline silicon module: 0.56%/°C and 0.35%/°C for m-Si and CIGS modules, respectively. The obtained results revealed strong influence of irradiance and temperature on energy production by PV panels. Performed studies have a large field of potential application and could improve designing process of PV installation.

Extremely Efficient Design of Organic Thin Film Solar Cells via Learning-Based Optimization

Design of efficient thin film photovoltaic (PV) cells require optical power absorption to be computed inside a nano-scale structure of photovoltaics, dielectric and plasmonic materials. Calculating power absorption requires Maxwell’s electromagnetic equations which are solved using numerical methods, such as finite difference time domain (FDTD). The computational cost of thin film PV cell design and optimization is therefore cumbersome, due to successive FDTD simulations. This cost can be reduced using a surrogate-based optimization procedure. In this study, we deploy neural networks (NNs) to model optical absorption in organic PV structures. We use the corresponding surrogate-based optimization procedure to maximize light trapping inside thin film organic cells infused with metallic particles. Metallic particles are known to induce plasmonic effects at the metal–semiconductor interface, thus increasing absorption. However, a rigorous design procedure is required to achieve the best performance within known design guidelines. As a result of using NNs to model thin film solar absorption, the required time to complete optimization is decreased by more than five times. The obtained NN model is found to be very reliable. The optimization procedure results in absorption enhancement greater than 200%. Furthermore, we demonstrate that once a reliable surrogate model such as the developed NN is available, it can be used for alternative analyses on the proposed design, such as uncertainty analysis (e.g., fabrication error).

Analysis Method for the Uniformity of a-Si-Based Multijunction Thin-Film Solar Module Using Ideality Factors

A methodology was developed to analyze the uniformity properties of amorphous silicon (a-Si) based triple-junction thin-film solar module for power stations or for building-integrated photovoltaic using circuit model parameters. First, a-Si-based triple-junction thin-film solar module with a size of 5G was fabricated via the mass production method. The module was divided into small modules with ten solar cells. A total of nine samples were selected and the dark I–V characteristics for each sample were measured. A circuit model for a triple-junction solar module was proposed. One sample that could represent the triple-junction properties was selected and the circuit parameters were extracted. The circuit model with the extracted parameters was simulated using H-spice and showed good agreement between experimental and simulation results. Ideality factors and reverse saturation currents from the selected samples were extracted from the dark IV curve and resistance parameters by using the numerical method with the circuit model. The distribution of each parameter for the samples and the uniformity of the large-size module were analyzed.

Tailoring Nano-Textures for Optimized Light In-Coupling in Liquid Phase Crystallized Silicon Thin-Film Solar Cells

Thin-film solar cells based on liquid phase crystallized silicon (LPC Si) with 8–20 μm thick absorber layers demand for advanced light management to achieve high photocurrent densities. Open-circuit voltages (Voc) >600 mV underline the high silicon material quality of LPC silicon thin-films on nano-textured glass superstrates. We present a 500 nm-pitched sinusoidal nano-texture which outperforms larger pitched gratings with respect to light in-coupling at the buried glass-silicon interface. In the wavelength range of interest reflection of incident light is minimized to values close to 4%, which is the reflection at the sun-facing air-glass interface. Further, the electronic material quality of sinusoidally textured devices is analyzed on basis of a comparison of maximum achieved open-circuit voltages on different texture types. The Voc on sinusoidally textured glass superstrates could be raised to 630 mV by changing the interlayer deposition method from a PVD to a PECVD process. Thus, we are able to unify high optical and electronic properties of silicon absorber layers on sinusoidaly textured glass substrates. These results constitute a crucial step toward fully exploiting the optical potential of LPC silicon thin-film solar cells.

Improvements in world-wide intercomparison of PV module calibration

Abstract The calibration of the electrical performance of seven photovoltaic (PV) modules was compared between four reference laboratories on three continents. The devices included two samples in standard and two in high-efficiency crystalline silicon technology, two CI(G)S and one CdTe module. The reference value for each PV module parameter was calculated from the average of the results of all four laboratories, weighted by the respective measurement uncertainties. All single results were then analysed with respect to this reference value using the En number approach. For the four modules in crystalline silicon technology, the results agreed in general within ±0.5%, with all values within ±1% and all En numbers well within [−1, 1], indicating further scope for reducing quoted measurement uncertainty. Regarding the three thin-film modules, deviations were on average roughly twice as large, i.e. in general from ±1% to ±2%. A number of inconsistent results were observable, although within the 5% that can be statistically expected on the basis of the En number approach. Most inconsistencies can be traced to the preconditioning procedure of one participant, although contribution of other factors cannot be ruled out. After removing these obvious inconsistent results, only two real outliers remained, representing less than 2% of the total number of measurands. The results presented show improved agreement for the calibration of PV modules with respect to previous international exercises. For thin-film PV modules, the preconditioning of the devices prior to calibration measurements is the most critical factor for obtaining consistent results, while the measurement processes seem consistent and repeatable.

Compatibility study towards monolithic self-charging power unit based on all-solid thin-film solar module and battery

Aiming at the development of a monolithic integrated all-solid-state self-rechargeable power unit, we perform a V-I characteristics compatibility study for the integration of such a device having a thin-film silicon multi-junction photovoltaic (PV) module and a thin-film solid Li//lithium phosphorus oxynitride//LiCoO2 battery. The battery and PV module are connected to mimic a monolithic module-to-storage cell device and the performance of this device in various temperature conditions has been tested. Few issues regarding the matching of the battery and PV module characteristics are identified for improvement. The concept of the integrated all-solid-state PV-battery solution appears viable especially in three-terminal device configuration.

Thermal energy conversion using near-field thermophotovoltaic device composed of a thin-film tungsten radiator and a thin-film silicon cell

In this paper, we proposed a novel nano-gap thermophotovoltaic (TPV) device made up of thin-films including the radiator. The optical, electrical, and thermal responses and performance of the device were assessed using coupled opto-electro-thermal numerical simulation. The device design consists of a thin-film tungsten radiator which is paired with a thin-film silicon TPV cell across a nanometric vacuum gap. Results were simulated based on experimental properties available in the current literature database. It is discovered that the maximum electrical power output of the thin-film nano-gap TPV device increases with cell temperature up to a certain threshold value due to improvements in generated photocurrent. Thin-film tungsten as a radiator is shown to improve radiative heat transfer above the bandgap compared to conventional bulk tungsten. The effect of cell thickness on responses and performance was also analysed. A 1-μm cell produces better performance over thinner thicknesses at the cost of greater cooling requirements. However, the improvements in output power offset the cooling costs, allowing for consistently favourable efficiencies. Finally, it is shown that the temperature profile in silicon thin-films under convective cooling can be approximated as uniform, simplifying the heat transport modelling process.

An Accurate and Fast Computational Algorithm for the Two-diode Model of PV Module Based on a Hybrid Method

This paper proposes an improved hybrid method to compute the parameters of the two-diode model of photovoltaic (PV) module. Unlike previous methods, it attains the speed of the analytical approach by utilizing only datasheet information. Furthermore, its accuracy is not compromised as it does not require simplifications in its computation. Four parameters are determined analytically, while the remaining three are optimized by using an evolutionary algorithm, i.e., the differential evolution. The speed is improved because the parameters are optimized only once, i.e., at standard test condition, while the values at other conditions are computed analytically. Furthermore, a procedure to guide the initial conditions of the Newton–Raphson iteration is introduced. For validation, the algorithm is compared to other established computational methods for mono-, polycrystalline, and thin film modules. When evaluated against the experimental data, the mean absolute error is improved by one order of magnitude, while the speed is increased by approximately threefold. The standard deviation of the decision parameters over 100 independent runs is less than 0.1—which suggests that the optimization process is very consistent. Due to its speed and accuracy, the method is envisaged to be useful as a computational engine in PV simulator.

Time-dependent changes in copper indium gallium (di)selenide and cadmium telluride photovoltaic modules due to outdoor exposure

The performance of photovoltaic (PV) modules deteriorates with time due to outdoor exposure. We investigated the time-dependent changes in PV modules and evaluated the amount of power generated during their lifetime. Once a year, the exposed modules were removed and measured under standard test conditions using a solar simulator. Their outputs were measured indoors and normalized to nominal values. In addition, the relationship between the indoor measurement and the energy yield for thin-film PV modules will be reported. In CIGS PV modules, the normalized maximum power (PMAX) and performance ratio (PR) differ with the type of module. The PMAX and PR of CdTe PV modules significantly decrease after outdoor exposure for three years. These results help to determine the characteristics of the time-dependent changes in the PMAX of PV modules due to outdoor exposure.

Solution Processed p-Type Cu2ZnSnS4 Thin Films for Absorber Layer

Thin films of quaternary chalcogenide Cu2ZnSnS4 (CZTS) were prepared due to its abundance and non-toxic nature by chemical spray pyrolysis technique with 2-methoxyethanol as solvent for the precursor solution that avoids the insoluble base by-products of zinc and tin. The solution was clear without precipitates as the solvent has higher viscosity compared to DI water which resulted in the successful deposition of smoother films. The structural, morphological, optical and electrical properties of the films at different temperatures 280, 300, 350 and 400 °C were investigated. The structural formation of kesterite Cu2ZnSnS4 was confirmed with a preferential (112) phase and with an intensed 334 cm−1 Raman frequency mode.Uniform film growth and crack-free surface was obtained at a temperature of 350 °C which was confirmed from morphological studies. The optical absorption showed a continuous absorption in the UV–Visible region and the obtained band gap for the films was in the range of 1.45–1.62 eV. The electrical study using Hall measurement proved the p-type conductivity of CZTS thin films which is pertinent for an absorber layer in thin film photovoltaic cell. A p–n junction was formed with TiO2 and CZTS materials and the light and dark current response was studied.

Noncovalent Se···O Conformational Locks for Constructing High‐Performing Optoelectronic Conjugated Polymers

Noncovalent conformational locks are broadly employed to construct highly planar π-conjugated semiconductors exhibiting substantial charge transport characteristics. However, current chalcogen-based conformational lock strategies for organic semiconductors are limited to S···X (X = O, N, halide) weak interactions. An easily accessible (minimal synthetic steps) and structurally planar selenophene-based building block, 1,2-diethoxy-1,2-bisselenylvinylene (DESVS), with novel Se···O noncovalent conformational locks is designed and synthesized. DESVS unique properties are supported by density functional theory computed electronic structures, single crystal structures, and experimental lattice cohesion metrics. Based on this building block, a new class of stable, structurally planar, and solution-processable conjugated polymers are synthesized and implemented in organic thin-film transistors (TFT) and organic photovoltaic (OPV) cells. DESVS-based polymers exhibit carrier mobilities in air as high as 1.49 cm2 V-1 s-1 (p-type) and 0.65 cm2 V-1 s-1 (n-type) in TFTs, and power conversion efficiency >5% in OPV cells.