Reactive ion etching texturing(RIE texturing) using SF6/O2 gas mixtures which had anisotropic etching characteristic has been studied to reduce surface reflectance of multi-crystalline silicon(mc-Si) solar cell by formation of homogeneous surface features since conventional wet texturing could not b...
Reactive ion etching texturing(RIE texturing) using SF6/O2 gas mixtures which had anisotropic etching characteristic has been studied to reduce surface reflectance of multi-crystalline silicon(mc-Si) solar cell by formation of homogeneous surface features since conventional wet texturing could not be applied to mc-Si with randomly orientated grains. However, RIE texturing with SF6/O2 gas had process time above 10 min which was slow process for high throughput industrial applications and it was difficult to control shape of surface features due to weak sidewall passivation which was consisted of SiOxFy volatilized below 0 ℃. To overcome these problems, RIE texturing using SF6/O2/Cl2 gas was employed and process time was limited for 5 min. RIE texturing using SF6/O2/Cl2 gas formed reaction products on surface features which were expected to play a role of mask and these were possible to form various surface features by controlling size of reaction products which was varied as a function of RIE set-up parameters. As results of RIE texturing, we could form needle-like(needle), pyramid, round-top cone(cone), and inverted pyramid structures. Among these structures, needle, pyramid, and cone structures were applied to fabricate RIE-textured mc-Si solar cell and reference cell without RIE texturing was fabricated in same solar cell fabrication process in order to compare with RIE-textured cells. The RIE-textured cell with cone structures represented the highest efficiency as 17.26 % and that with pyramid structures was 16.86 % whereas, efficiency and all performances of cell with needle structures was degraded when compared to reference cell. The increase of Jsc and fill factor(FF) caused to increase efficiency of cells with cone and pyramid structures. The lower efficiency of cell was, the higher density of breakdown site, which was observed in electroluminescence(EL) images, and reverse current density were. Their Rsh extracted from impedance spectra supported such trend for efficiency and leakage current. It deduced from the results for Rsh, EL, reverse current density, and phosphorus silicate glass(PSG) images that needle structures, which caused the lowest efficiency and the highest reverse current density, was unsuitable to conventional solar cell fabrication process. The average grain size of mc-Si was between 3 and 4 ㎜ and there was efficiency margin of 0.1 % per 0.5 ㎜. Bulk defect like dislocation and impurity precipitation caused to decrease EQE for wavelength above 550 ㎚. HF/HNO3/de-ionized wafer(HND) saw damage removal(SDR) process was more efficient to apply RIE texturing than KOH SDR. In this thesis, we tried to control size of reaction product and shape of surface features by Cl2 addition to conventional RIE texturing and hence, needle, pyramid, cone, and inverted pyramid were formed. The efficiency of RIE-textured cells with pyramid and cone structures increased by 0.6 and 1 %, respectively, compared to that of reference cell. It showed feasibility of industrial application of RIE texturing to achieve high-efficiency mc-Si solar cell.
Reactive ion etching texturing(RIE texturing) using SF6/O2 gas mixtures which had anisotropic etching characteristic has been studied to reduce surface reflectance of multi-crystalline silicon(mc-Si) solar cell by formation of homogeneous surface features since conventional wet texturing could not be applied to mc-Si with randomly orientated grains. However, RIE texturing with SF6/O2 gas had process time above 10 min which was slow process for high throughput industrial applications and it was difficult to control shape of surface features due to weak sidewall passivation which was consisted of SiOxFy volatilized below 0 ℃. To overcome these problems, RIE texturing using SF6/O2/Cl2 gas was employed and process time was limited for 5 min. RIE texturing using SF6/O2/Cl2 gas formed reaction products on surface features which were expected to play a role of mask and these were possible to form various surface features by controlling size of reaction products which was varied as a function of RIE set-up parameters. As results of RIE texturing, we could form needle-like(needle), pyramid, round-top cone(cone), and inverted pyramid structures. Among these structures, needle, pyramid, and cone structures were applied to fabricate RIE-textured mc-Si solar cell and reference cell without RIE texturing was fabricated in same solar cell fabrication process in order to compare with RIE-textured cells. The RIE-textured cell with cone structures represented the highest efficiency as 17.26 % and that with pyramid structures was 16.86 % whereas, efficiency and all performances of cell with needle structures was degraded when compared to reference cell. The increase of Jsc and fill factor(FF) caused to increase efficiency of cells with cone and pyramid structures. The lower efficiency of cell was, the higher density of breakdown site, which was observed in electroluminescence(EL) images, and reverse current density were. Their Rsh extracted from impedance spectra supported such trend for efficiency and leakage current. It deduced from the results for Rsh, EL, reverse current density, and phosphorus silicate glass(PSG) images that needle structures, which caused the lowest efficiency and the highest reverse current density, was unsuitable to conventional solar cell fabrication process. The average grain size of mc-Si was between 3 and 4 ㎜ and there was efficiency margin of 0.1 % per 0.5 ㎜. Bulk defect like dislocation and impurity precipitation caused to decrease EQE for wavelength above 550 ㎚. HF/HNO3/de-ionized wafer(HND) saw damage removal(SDR) process was more efficient to apply RIE texturing than KOH SDR. In this thesis, we tried to control size of reaction product and shape of surface features by Cl2 addition to conventional RIE texturing and hence, needle, pyramid, cone, and inverted pyramid were formed. The efficiency of RIE-textured cells with pyramid and cone structures increased by 0.6 and 1 %, respectively, compared to that of reference cell. It showed feasibility of industrial application of RIE texturing to achieve high-efficiency mc-Si solar cell.
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#RIE texturing
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