Abstract
Contact-end voltage measurement was applied to characterize the contact-formation process of silver paste metallization on p- and n-type crystalline silicon solar cells under different temperatures with well-designed fixtures and test patterns based on the circular transmission line model. The contact-end voltage values were found to be sensitive to sintering temperature, and the current density and contact end voltage curves of both contacts were linear, stating that the contacts were ohmic contacts. Their symbols on the n-type emitter reversed from negative to positive under the established connection mode, which indicated conductive-path changes manifested in the form of macroscopic electrical properties under insufficient, optimal, and over-fired conditions. We inferred that the conductive channel variations were mainly caused by the silver crystallites that precipitated on the emitter surface from the combination of the cross-sectional and interface morphology analyses. No similar phenomenon was observed on the p-type emitter for the few silver crystallites or silver-aluminum alloy without conductive-path alternation. Their values were much greater than those of the n-emitter, which agreed with the present industrial n-type cell characteristics. The measurement improved our understanding of the contact formation process, and can be used as a flexible approach for researchers to optimize the silver-paste formula and sintering processes for high-efficiency solar cells.
Highlights
Screen-printing thick-film metallization has been applied in silicon solar cells in accordance with the firing-through fundamental of antireflection coating on the emitter surface of cells due to the glass frits mixed in the silver paste.[1]
We focused on the contact-end voltage (CEV) measurement under different peak sintering temperatures, explored its use to characterize the metallization of p- and n-type silicon solar cells, and investigated the majority carrier-transfer channels in combination with the interface analysis
The n-type emitter baseline sample was fired in a product line that represented the best comprehensive performance in terms of the cells, where the absolute CEV values was approximately 0.11 mV
Summary
Non-uniform sheet resistance, internal line resistance of the fingers, and so on, all of them lead to inaccurate results and need to be corrected.[7] Recently, Xiong et al applied Reeves’s pattern of concentric rings based on circular transmission line model (CTLM) to extract ρc, Rsk, and transfer length Lt just assuming that the current distribution is uniform between the concentric circular contacts.[8] The CTLM method demonstrated its advantages in terms of sample preparation with only once screen printing,[9] and completeness in extracting the total key parameters related to contact resistance with the least assumptions, whereas the extraction remains complex, whether RTLM or CTLM is used.
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