He Wang

In this article, the electrochemical corrosion of full‐area aluminum back‐surface field (Al–BSF) and bifacial passivated emitter and rear cell (PERC) crystalline silicon (c‐Si) solar cells subjected to different potential in sodium chloride (NaCl) solution is systematically investigated. Based on different potential‐induced corrosion, the electrochemical corrosion mechanism of c‐Si solar cells is revealed for the first time. Under zero potential, an important finding is that the silicon beneath silver electrode is corroded and perforated for Al–BSF cells. This phenomenon is attributed to the interaction between hydroxide ions from galvanic corrosion and electrons from silicon corrosion. For bifacial PERC cells, the pyramidal structure of silicon surface beneath the aluminum finger is observed at zero potential, which is similar to the silicon texturing etched in alkaline environment. Additionally, it is found that silicon corrosion is inhibited when positive or negative potential is applied to the back of Al–BSF and bifacial PERC cells. Moreover, it is observed the aluminum suffers from more serious corrosion at positive potential than that at zero or negative potential, which is attributed to synthetical results of galvanic corrosion and electrolytic corrosion. In this work, a new insight on the potential‐induced electrochemical corrosion for c‐Si solar cells is provided.

In this paper, the bifaciality factor and ideality factor of PERC bifacial solar module are investigated under different irradiances. By measuring the electrical performance under different irradiances, it is found that the bifaciality factor of PERC bifacial solar module increases when the irradiance increases. Meanwhile, the ideality factor of PERC bifacial solar module under different irradiances is obtained according to the single-diode model. It is found that the ideality factor of PERC bifacial solar module increases as irradiance intensity increases under the same temperature. The results are beneficial to understand the performance of PERC bifacial solar module in the field.

In this article, the temperature coefficients of the bifacial passivated emitter and rear cell (PERC) solar module and the full-area aluminum back surface field (Al-BSF) solar module were calculated based on the theoretical model under different module temperatures and irradiances. Meanwhile, the measured temperature coefficients were obtained by testing the performance of bifacial PERC solar module and conventional Al-BSF solar module under different module temperatures and irradiances. The results show that the laboratory measurements are close to the calculated values, and the normalized temperature coefficients of output power for the bifacial PERC solar module are lower than that of the conventional Al-BSF solar module under the same operating conditions. An interesting finding is that the normalized temperature coefficients of short-circuit current for the bifacial PERC solar module are larger than that of the conventional Al-BSF solar module under the same irradiance. This is attributed to lower back surface recombination velocity and higher carrier collection efficiency of PERC solar cells compared with conventional Al-BSF solar cells. Additionally, the operating temperatures of the bifacial PERC solar module and conventional Al-BSF solar module were surveyed outdoor. It is found that the operating temperature of the bifacial PERC solar module is higher than that of the conventional Al-BSF solar module in some cases. However, this tendency is reversed in other cases when these two solar modules work under the same environmental conditions. The conclusion was explained reasonably according to the actual operating conditions of solar modules. The obtained results in this work can provide useful insight into evaluating the field performance of the bifacial PERC solar module.

Potential induced degradation (PID) leads to power degradation, and reduces durability and reliability of solar modules. However, this problem has not been thoroughly solved so far. The results from interlaboratory and field study show contradictory fault phenomenon for PID. In this paper, PID of crystalline silicon photovoltaic power plants distributed in various climate conditions was investigated. These photovoltaic power plants consist of two types of crystalline silicon solar modules, which cover almost all kinds of front glass, ethyl vinyl acetate (EVA) and backsheet available commercially. It was found that only a few of power plants were affected by PID. By measuring current voltage characteristics of PID-affected solar modules, the real faults phenomenon was uncovered and classified into regular and irregular power degradation in a module string. The results obtained in this work show that the negative potential caused by high system voltage and stacking faults are necessary and sufficient conditions for PID occurrence for the first time. The anomalous power degradation is related to the stacking fault, which appears randomly during the crystal growth.

The regular performance deterioration of P-type crystalline silicon solar modules and module strings caused by potential-induced degradation in a photovoltaic power plant was found in the field. The PID-affected solar modules dismounted from the photovoltaic power plant were further investigated systematically in the laboratory. For the first time, we found that the neutral point of voltage in a module string moved forward to the positive pole for a PID-affected module string as time goes on. Even if low positive voltage is applied to a PID-prone module, it could cause PID. The thermographic and electroluminescence (EL) images of a PID-affected module string also exhibit a regular degradation pattern. This is in good agreement with the measured power loss of the dismounted solar modules under standard test conditions. The results obtained in this paper show that the maximum power degradation rate of solar modules was as high as 53.26% after only one year of operation because of PID in the field. Due to the vast amount of solar modules and incomplete recovery, this is a terrible catastrophe for the owner of a power plant and module producer.

At present, the improvement in performance and the reduction of cost for crystalline silicon solar cells are a key for photovoltaic industry. Passivated emitter and rear cells are the most promising technology for next-generation commercial solar cells. The efficiency gains of passivated emitter and rear cells obtained on monocrystalline silicon wafer and multicrystalline silicon wafer are different. People are puzzled as to how to develop next-generation industrial cells. In this paper, both monocrystalline and multicrystalline silicon solar cells for commercial applications with passivated emitter and rear cells structure were fabricated by using cost-effective process. It was found that passivated emitter and rear cells are more effective for monocrystalline silicon solar cells than for multicrystalline silicon solar cells. This study gives some hints about the industrial-scale mass production of passivated emitter and rear cells process.

Based on the theory of material mechanics and thermal stress analysis, the stress distribution of combined electrode for crystalline silicon solar module was studied for the first time. The shear stress and normal stress distribution of soldered structure for crystalline silicon solar cells under the thermal field were discussed. And the results show that the stress distribution is not simply linear relationship as some results found. But there is a stress concentration at the edge, which was considered as the true reason that caused microcracks at the edge of soldered solar cells. The conclusions we got in this paper provide a theoretical basis for deceasing the breakage rates of soldered crystalline silicon solar cells and improving the reliability of crystalline silicon solar modules.

During the course of solar module encapsulation, the output power of crystalline silicon solar module is less than the sum of the maximum output power of the constituents because of power loss. So it is very important to investigate the power loss caused by encapsulation materials and module production process. In this paper, the power loss of crystalline silicon solar module is investigated by experiments systematically for the first time. It is found that the power loss is mainly caused by the resistance of ribbon and mismatch of solar cells; the total power loss is as high as 3.93% for solar module composed of 72 cells (125 mm × 125 mm) connected in series. Analyzing and reducing the power losses are beneficial to optimizing encapsulation process for the solar module. The results presented in this study give out a direction to decreasing power loss and optimizing encapsulation process of crystalline silicon solar module.