Gallium-Doped CZ Silicon Substrate Processing for Minority Carrier Lifetime
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Solution Overview
Problem
Silicon single crystal substrates with higher oxygen concentrations experience defects due to oxygen, leading to a decrease in minority carrier lifetime, which degrades the characteristics of solar cells.
Innovation Solution
A method involving 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 the growth of oxygen-induced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal treatment is performed at 800°C or more on silicon single crystal substrate containing oxygen, then emitter layer formation or oxide film formation is achieved, but oxide precipitate defects grow causing decrease in minority carrier lifetime
Solution Approach 1:
The invention applies preliminary high-temperature thermal treatment (1200°C or more for 30 seconds or more) before the low-temperature thermal treatment (800°C to 1100°C) to dissolve oxide precipitate nuclei in advance. This preliminary action prevents the growth of oxygen-induced defects during the subsequent emitter layer formation process, thereby resolving the contradiction between achieving proper emitter layer formation and maintaining minority carrier lifetime.
2Reliability
If high temperature thermal treatment (1200°C or more) is applied to dissolve oxide precipitate nuclei, then minority carrier lifetime is maintained, but additional process time and energy consumption increase
Solution Approach 1:
The invention changes the temperature parameter to 1200°C or more for the preliminary thermal treatment, which is sufficiently high to rapidly dissolve oxide precipitate nuclei within 30 seconds or more. By optimizing both temperature and time parameters, the process achieves effective dissolution of oxide precipitates while minimizing the additional process time required, thus maintaining minority carrier lifetime without excessive time loss.
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
This method effectively prevents the 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
Implementation Method 3
the emitter layer is formed by vapor-phase diffusion of POCl3 or coating diffusion of phosphoric acid-base material
Implementation Method 4
forming an oxide film on the substrate surface
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.