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Xi X.,Jiangnan University | Xi X.,Suntech Power | Xi X.,Optoelectronic Engineering and Technology Research Center | Chen X.,Suntech Power | And 8 more authors.
Solar Energy

N-type solar cells with aluminum rear emitter provide high power conversion efficiency and overcome light induced degradation. Meanwhile, since the processes are realized on the existing P-type cells, the fabrication cost gets lower for N-type solar cells. Front surface field (FSF) is an important part in this structure. The functions of FSF are similar to that of Al back surface field in P-type cells. FSF enhances carrier collection ability, increases the cells' open-circuit voltage, as well as increases the efficiency. In this paper, the FSF profiles were investigated. The appropriate surface concentration was around 4×1020cm-3, meanwhile the depth should be kept between 0.25μm and 0.3μm from the experiment. A too low concentration cannot provide a strong field effect passivation, while a too high concentration will introduce much more recombination centers. A thin FSF layer increased the resistance, while a thick FSF layer made the short-circuit current decrease, because of the degradation of photoelectric response at the short wavelength. Thermal oxidation was introduced in the process. The FSF profiles were also studied. The minority lifetime and efficiency were enhanced after oxidation. The surface concentration of FSF should be adjusted to around 3×1019cm-3. The best cell efficiency has reached to 19.93%, tested by 18th Institute of China Electronics Group Corporation. © 2015 Elsevier Ltd. Source

Xi X.,Jiangnan University | Xi X.,Suntech Power | Xi X.,Optoelectronic Engineering and Technology Research Center | Chen X.,Suntech Power | And 9 more authors.
Journal of Renewable and Sustainable Energy

For normal solar cell production, the front surface is upturned and the Al rear surface directly contacts with the belt during the firing process. In this paper, the influence of metallic belt on the Al back surface field was investigated. With the development of light induced plating technology, it was possible that the rear surface was upturned so that the rear surface would not directly contact with the belt. For normal structured P-type cells, the rear surface upturned (RSU) method narrowed conversion efficiency distribution. With the efficiency growing, the advantages of RSU were seen more clearly. For Al rear emitter N-type solar cells, RSU was good for the quality of rear junction. The internal quantum efficiency at the long wavelength was improved a lot. The average efficiency increased by about 0.2%(abs). The best efficiency increased to 19.93%. Additionally, RSU also reduced the rear surface void ration in passivated emitter and rear contact (PERC) cells. The average efficiency of RSU PERC cells also increased by about 0.2%(abs). The best efficiency of PERC cells with RSU method was improved to 20.38%. The most important improvement came from the rear contact. In this paper, the environment tolerance of the cells was also studied. The thimbles of the belt destroyed the Al film and made the film loose. RSU method avoided direct contact of the Al film and the belt, and made the Al films compacter during the firing process. The performances of the cells in a hot and humid environment were improved. The aspects of rear surface almost did not change after water boiling. The efficiency degradation was lower than that of the normal firing mode. RSU method was good both for the cells' efficiency and the stability improvement. © 2015 AIP Publishing LLC. Source

Xi X.,Jiangnan University | Xi X.,Suntech Power | Xi X.,Optoelectronic Engineering and Technology Research Center | Chen X.,Suntech Power | And 7 more authors.
Applied Surface Science

A stratification phenomenon of aluminum rear alloyed layer was found in the study of aluminum rear emitter N-type solar cells. It is related to the composition of the paste. The outer aluminum alloyed layer can be called as aluminum doped emitter, and it gives the contribution to the junction formation. The inner layer is only the Al/Si mixed layer. The aluminum atoms in this layer are not bonded with silicon atoms. This inner layer will ruin the quality of the rear junction. The shunt resistance, reverse current density and the junction electric leakage value are getting worse when the thickness of the inner layer increases. The thickness of the inner Al/Si mixed layer increases with the increasing of firing temperature, while the depth of the aluminum doped emitter almost does not change. From the analyses, the inner Al/Si mixed layer is redundant and deleterious. Only a single deep aluminum doped rear emitter is needed for N-type solar cells. The highest power conversion efficiency of 19.93% for aluminum rear emitter N-type cells without the stratification phenomenon has been obtained. © 2015 Elsevier B.V. All rights reserved. Source

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