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The silicon wafers for solar cells on which the paste is deposited experience a bowing phenomenon. The thickness of commonly used c-Si wafers is 180 μm or more. When fabricating c-Si solar cells with this wafer thickness, the bowing value is 3 mm or less and the problem does not occur. However, for the thin c-Si solar cells which are being studied recently, the output reduction due to failure during manufacture and cracking are attributed to bowing. In generally, it is known that the bowing phenomenon arises mainly from the paste applied to the back side electrode of c-Si solar cells and the effects of SiNx (silicon nitride) and the paste on the front side are not considered significant. The bowing phenomenon is caused by a difference in the coefficient of expansion between heterogeneous materials, there is the effect of bowing on the front electrode and ARC. In this paper, a partially processed c-Si solar cell was fabricated and a bowing phenomenon variation according to the wafer thicknesses was confirmed. As a result of the experiment, the measured bow value after the firing process suggests that the paste on the front-side indicates a direction different from that of the back-side paste. The bow value increases when Al paste is deposited on SiNx. The fabricated c-Si solar cell was analyzed on basis of the correlation between the bowing phenomenon of the materials and the c-Si wafer using Stoney's equation, which is capable of analyzing the relationship between bowing and stress. As a result, the bowing phenomenon of the c-Si solar cell estimated through the experiment that the back side electrode is the important element, but also the front electrode and ARC influence the bowing phenomenon when fabricating c-Si solar cells using thin c-Si wafers. [ABSTRACT FROM AUTHOR]

Several studies have aimed to develop methods for recycling and recovering valuable materials from waste photovoltaic (PV) modules to keep up with the increasingly stringent waste disposal guidelines. However, silicon (Si) recovered from disposed PV modules is rarely used as a raw material in the solar industry. In this study, 30 % Si recovered from waste PV modules was added to a feedstock to grow a 6inch single-crystalline Si ingot using the Czochralski method. The single-crystalline Si ingot was re-melted and manufactured to produce a higher quality single-crystalline Si ingot with a minority carrier lifetime of 274–1527 μs and purity of 7N7. Thereafter, a Si wafer was manufactured via cropping, squaring, and wafering. Finally, the Si wafer was used to fabricate a solar cell via a conventional process. Solar cell parameters, such as open circuit voltage, short circuit current density, fill factor, and efficiency, were analyzed using a solar simulator. The manufactured solar cell had an efficiency of 20.05 %, which is approximately 0.97 % lower than that of commercial wafer-based solar cells. Moreover, the factors influencing the solar cell efficiency were evaluated. The proposed study involved the production of a silicon ingot using silicon scraps recovered from a waste solar module. Subsequently, a solar cell was manufactured, and its efficiency was evaluated through a conventional solar cell manufacturing process. The ingot production process involved a mixture of virgin silicon and recycled silicon scraps at a ratio of 7:3, followed by the repetition of the Czochralski method to produce a high-quality silicon ingot. During this process, the concentration of metal and non-metal impurities, as well as the electrical characteristics, were evaluated. The manufactured solar cell exhibited excellent PV performance, achieving a high efficiency of 20.05 %, which is the highest among solar cells manufactured using recycled silicon scraps. [Display omitted] • Single-crystalline Si ingot prepared using Si recovered from waste PV module. • Characteristics of a solar cell fabricated from Si ingot are evaluated. • Manufactured solar cell exhibits efficiency of 20.05 %. • Efficiency is 0.97 % lower than that of commercial wafer-based solar cell. [ABSTRACT FROM AUTHOR]

Abstract This study presents the electrorefining of Ag from a crystalline silicon solar cell in a silver nitrate (AgNO 3) electrolyte solution at 25 °C and an evaluation of the morphology and cathodic efficiency. The equilibrium potential was determined by cyclic voltammetry in order to calculate the cathodic overpotential. Pure Ag deposits with a single phase, as defined by X-ray diffractometry, could be obtained from all experiments with cathodic efficiencies in the range 89.5–95%. The morphology of the Ag particles recovered on the cathode changed from granules to dendrites with increasing applied current density. Granular particles were observed under applied current densities of 1 and 3 mA cm−2. Meanwhile, dendritic particles were formed at higher applied current densities of 5, 7, and 10 mA cm−2. Cathodic efficiency tended to decrease because of hydrogen coevolution and dendritic growth during electrorefining at higher applied current densities. The critical overpotential was calculated in order to find the optimal cathode overpotential to obtain high-purity Ag deposits with high cathodic efficiency. Highlights • Various current densities were applied in electrochemical recovery of silver. • Silver deposits were obtained from experiments with high cathodic efficiency. • Silver deposits changed from granular to dendritic with increased current density. • The critical overpotential was calculated to find the optimum processing condition. [ABSTRACT FROM AUTHOR]

Thin crystalline silicon (c-Si) photovoltaic (PV) cells (< 100 µm) have the potential to curtail manufacturing costs by reducing the amount of Si needed per wafer. However, thermo-mechanical stress induced by high-temperature (> 200 °C) soldering causes frequent wafer breakage in thin c-Si-based modules. Hence, in this work, we proposed low-temperature interconnection method using conductive paste (CP) for thin c-Si PV modules and systematically studied the modules’ electrical and mechanical properties as a function of annealing temperature of CP. The potential advantage of this method is significantly reduced wafer bowing due to the low-temperature tabbing (< 150 °C) of CP dispensed cells to ribbons using heat and pressure during lamination. Module degradation and peel stress tests indicated that CP cured above its melting point provides stable (degraded 3.0% after 500 h damp heat test) and efficient current flow paths. By contrast, CP annealed below the melting point is vulnerable to thermal and humidity stress, leading to 7.8% degraded output after the test. Given these features, stable, large modules with thin c-Si cells integrated using a CP approach (laminated at 150 °C) were successfully realized without cell breakage. [ABSTRACT FROM AUTHOR]

Research efforts to overwhelmingly fortify the economics of photovoltaics have focused on increasing the light-to-electricity conversion efficiency and reducing the overall manufacturing costs. Since lowering the consumption of silicon has the potential to greatly curtail the material costs, studies on wafering thin silicon substrates have been performed. However, current methods to interconnect solar cells with metal ribbons are not sufficient to employ thin silicon wafers. Therefore, this study explores a novel route to interconnect solar cells with metal ribbons without thermomechanical stress using a highly conductive liquid metal. Galinstan, which is notoriously difficult to print, is successfully harnessed to be printable by suspending submillimetre-sized Galinstan droplets in the carrier vehicle, as aided by the yield stress. By mechanically sintering the Galinstan paste with gentle mechanical pressure, solar cells are interconnected with metal ribbons at room temperature. Albeit the averaged maximum power of the unit modules interconnected using the Galinstan paste was significantly degraded after just 100 thermal cycles due to the possible formation of resistive intermetallic compounds of Galinstan, the power degradation of the best unit module using the Galinstan paste is −0.9%, which is smaller than the averaged one of the unit modules using a conventional soldering method (-1.35%), implying the thermomechanical-stress-free interconnection method using a liquid metal has a chance to be improved for being a comparable competitor to the conventional soldering method. [ABSTRACT FROM AUTHOR]

Mismatch of solar cells that occurs during fabrication of the modules can lead to unavoidable power losses. However, it is difficult experimentally to identify incidences of power loss from solar cells that behave similarly due to measurement error. Power loss in a module is mainly affected by three mismatch factors: photocurrent, series, and shunt resistance levels. An equation to determine the output of a partially mismatched module using only the photocurrent and series resistance has been published. Here, a newly developed model that considers mismatch factors, including the shunt resistance, is proposed. The newly developed model was validated through a comparison of simulation results to the measured output of a module that includes solar cells with different low shunt resistances (within 0.4 A deviation for the output current of the module). The model was then applied to calculate the power loss occurring in a module according to minute differences between the three mismatch factors. Finally, we confirm that the maximum power, as well as the photocurrent, of solar cells should be considered to minimize cell-to-module conversion loss at the module production stage. [ABSTRACT FROM AUTHOR]

This study presents the re-fabrication of a crystalline silicon (c-Si) solar cell using a Si wafer reclaimed from the solar cell of an end-of-life (EoL) module, and an evaluation of its performance. A 6-in. commercial solar cell was used in the etching process by wet chemical process in order to investigate the optimal mixing ratio of a mixture of HNO 3 and HF. The silicon nitride (SiN x ) and aluminum (Al) back contact on both sides of the solar cell were not completely removed at a high ratio of aqueous HNO 3 , and the precipitation of Ag particles on the surface of Si wafer were deposited at a high ratio of aqueous HF in a mixed acid solution. The optimum etching condition for the recovery of the c-Si wafer was applied to the EoL module, which consisted of 4″ solar cells. The photovoltaic (PV) performance of the re-fabricated 4″ solar cell was measured by conventional solar cell processing, which shows the best results reported so far. The higher boron (B) concentration and reflectance of the re-fabricated solar cell reduced cell efficiency by 0.6% compared with the commercial 6″ solar cell. However, it has sufficient potential for use in the PV industry. [ABSTRACT FROM AUTHOR]

Environmentally friendly and reusable methanesulfonic acid (MSA) was used with the addition of an oxidizing agent to extract Ag from solar cells. Recovery using varying MSA:H 2 O 2 mixing ratios of 100:0, 90:10, 75:25, 50:50, and 0:100 revealed that Ag can be effectively extracted in a MSA-rich solution. The concentration of Ag ions dissolved in each mixture was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), which established that the optimal extraction condition is a MSA:H 2 O 2 ratio of 90:10. The addition of HCl to the leaching solution used for Ag recovery prompted the precipitation of AgCl, which was then reacted in turn with NaOH and H 2 O 2 to recover Ag metal powder. This Ag metal powder was analyzed by glow discharge mass spectrometry (GDMS) and found to have a low purity of around 99% (2N), but this was found to be improved through subsequent electrorefining to a purity of 99.995% (4N5). [ABSTRACT FROM AUTHOR]

This paper presents a metallurgical route that consumes much less energy than the gasification route such as Siemens process-based photovoltaic (PV) value chain including metallurgical-grade silicon (MG-Si), solar-grade silicon (SoG-Si) purified by the metallurgical route, Czochralski (Cz) ingot growth, 6″ wafer fabrication, solar cell fabrication, and PV performance evaluation. Mono-like crystalline silicon ingot for achieving high purity was continuously cast with MG-Si for the fabrication of feedstock for Cz ingot growth through the advanced electron beam melting (EBM) system. The system was developed with the combination of vacuum refining part and directional solidification (DS) part for the purification of large amounts of MG-Si, where the two parts are connected by an overflow of Si melts to undergo continuous refining and casting processes in a chamber. To grow the mono-like crystalline Si ingot in our EBM system, a single crystalline seed was placed on the graphite dummy cylinder with DS zone. The mono-like crystalline Si ingot with high purity of >99.999% (above 5N) was blended 50–50 with undoped SoG-Si chunk for the compensation of boron dopant concentration in a crucible of Cz grower. The 156 × 156 mm 2 wafers were cut from Cz ingot grown with purity of >99.99999% (above 7N) by slurry-based multi-wire sawing and were fabricated by the conventional solar cell process. The measured photovoltaic performance recorded cell efficiency of 17.1%; hence its higher potential for application to the PV industry. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new equation for electrical CTM loss is proposed. [•] The model for the output of solar cells with ribbon is validated. [•] The model for mismatching loss of solar cells in module is validated. [•] The model for coexist conditions with ribbon and mismatching is validated. [Copyright &y& Elsevier]

Despite the predominance of solar modules with bulk crystalline silicon solar cells as a result of their high photoconversion efficiency, long-lasting durability, and low cost per electrical watt, the competitive market has elevated the necessity of thinner silicon solar cells to further reduce direct material costs. However, the tabbing and stringing process using high melting temperature soldering in the conventional fabrication method of a silicon solar module is required to alternatingly interconnect adjacent silicon solar cells, which entails significant thermomechanical stress. The lifting up-and-down motions in the layup process of serially stringed silicon solar cells also lead to an unfavourable interfacial stress between metal ribbons and silicon solar cells. Consequently, a considerably poor yield of silicon solar modules with the unbearable breakage loss of thin silicon solar cells is ascribed to such processes. Herein, an innovative solution to interconnect thin silicon solar cells through virtually no thermomechanical stress is proposed by using encapsulants pre-attached with low melting temperature metal ribbons at 139 °C, which allow the interconnection of pre-laid silicon solar cells in the course of the vacuum lamination at 160 °C. The resulting silicon solar modules exhibit a photoconversion efficiency of 19.1 ± 0.1%, which represents 99.9 ± 0.6% of the benchmark photoconversion efficiency of conventional silicon solar modules. The presented layup-only modulization succeeds in fabricating silicon solar modules with 100 μm thin silicon solar cells and it is anticipated to curtail the breakage loss of thin silicon solar cells as well as elevate fabrication productivity by simplifying the fabrication steps of silicon solar modules. Image 1 • Layup-only modulization enables stress-free fabrication of a silicon solar module. • The fabrication steps are simplified without the tabbing and stringing process. • Interconnection occurs in the vacuum lamination at a low temperature of 160 °C. • Its performance is comparable to that of a conventional silicon solar module. • Silicon solar modules with 100 μm thin solar cells are successfully demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, the problems of PV arrays under partial shading and a short circuit failure of bypass diode were analyzed with modeling the mathematical equation by using simulation, and the electrical and thermal characteristics were analyzed in an outdoor with a module which fabricated assuming a real PV array. The simulation model shows the mismatch current due to a bypass diode failure is proportional to the number of fault diodes and parallel strings in PV arrays. From the results of a field experiment, a reverse current did not flow into the mismatching string under partial shading regardless of system operation status, but the temperature of bypass diode in the case of system operation was 15–23 °C higher than that of the other case. However, in case of the fault bypass diode with the system off, the reverse current of 17A flowed into a fault string. Besides, the surface temperature of fault bypass diode reached above 140 °C, and some solar cells within a fault string was 18 °C higher than normal strings. In this paper, we verified that the short circuit failure of bypass diode creates a mismatch loss in PV system, and the reverse current causes electric-thermal problems in PV array. • The electrical and thermal characteristics of mismatching PV arrays were analyzed. • The reverse current of PV arrays hardly flows due to partial shading. • As the short circuit failure of bypass diode increases, reverse current increases. • Reverse current rise temperature of solar cells and burned out faulty bypass diode. • Monitoring of fuse and bypass diode needs to prevent system output loss and accident. [ABSTRACT FROM AUTHOR]