Gallium-Doped CZ Silicon Substrates for Oxygen Defect Suppression
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Solution Overview
Problem
Thermal treatment of silicon single crystal substrates at 800° C. or higher leads to oxygen-induced defects, reducing minority carrier lifetime and degrading solar cell performance, particularly in substrates with higher oxygen concentrations.
Innovation Solution
Subjecting silicon single crystal ingots or substrates to high temperature thermal treatment at 1200° C. or more for 30 seconds or more before low temperature thermal treatment at 800° C. or more and less than 1200° C. to dissolve oxide precipitate nuclei, preventing defect growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thermal treatment is performed at 800°C or more to form emitter layer or oxide film, then the solar cell manufacturing process can be completed, but oxygen-induced defects grow and minority carrier lifetime decreases
Solution Approach 1:
The patent applies preliminary action by performing high-temperature thermal treatment (1200°C or more for 30 seconds or more) before the low-temperature thermal treatment (800°C to 1200°C) to dissolve oxide precipitate nuclei in advance. This preliminary dissolution prevents oxygen-induced defects from growing during subsequent manufacturing processes, thereby maintaining minority carrier lifetime while still enabling complete solar cell manufacturing.
2Quantity of substance
If high oxygen concentration is present in the substrate, then material availability is improved, but defect growth is accelerated and solar cell characteristics degrade
Solution Approach 1:
The patent converts the harmful effect of high oxygen concentration into a beneficial outcome by using the oxygen itself to form oxide precipitates that can be dissolved through high-temperature treatment. The high-temperature thermal treatment (1200°C or more) dissolves the oxide precipitate nuclei, transforming the potential harm of oxygen-induced defects into an opportunity to create a cleaner substrate with improved solar cell characteristics.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents decrease in minority carrier lifetime, thereby improving the conversion efficiency of solar cells manufactured using these substrates.
Implementation Method 1
subjecting the silicon single crystal ingot or the silicon substrate to high temperature thermal treatment at a temperature of 1200° C. or more for 30 seconds or more before the low temperature thermal treatment
Implementation Method 2
it is possible to previously dissolve oxide precipitate nuclei, which can be origins of oxide precipitation defects
Data Source
AI summary
A solar cell includes a light-receiving surface electrode formed on a light-receiving surface, a back surface electrode formed on a backside, and a CZ silicon single crystal substrate doped with gallium. The CZ silicon single crystal substrate contains 12 ppm or more oxygen atoms. A spiral oxygen-induced defect is not observed in an EL (electroluminescence) image of the solar cell.