Laser Annealing Photovoltaic Cell Doping
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Solution Overview
Problem
The manufacturing of photovoltaic cells with doped zones faces challenges due to the incompatibility of thermal activation temperatures for different dopants, leading to separate implantation and annealing steps that increase contamination risks and substrate degradation.
Innovation Solution
A method involving ion implantation of dopants on both faces of a semiconductor substrate, followed by localized thermal activation using laser irradiation to achieve the necessary temperatures without overheating the opposite face, allowing for simultaneous vacuum processing and reducing substrate degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate implantation and thermal annealing steps are used for different dopants, then the activation temperatures can be optimized for each dopant, but the contamination risk increases and substrate degradation occurs
Solution Approach 1:
The patent segments the thermal activation process by applying laser irradiation selectively to specific regions of the substrate. The laser activates dopants only in the targeted area (e.g., BSF region) while leaving other regions unaffected, thus avoiding global high-temperature exposure that causes contamination and degradation.
Solution Approach 2:
The patent replaces the conventional thermal field (heating炉) with a localized laser field. Instead of using a furnace that heats the entire substrate to high temperatures, a laser beam is used to provide localized thermal energy only where needed, eliminating the harmful effects of global high-temperature processing.
2Reliability
If high temperature thermal annealing is applied to activate boron dopants, then the boron activation is effective, but the overall substrate lifetime is degraded
Solution Approach 1:
The patent applies local quality by providing different thermal treatments to different regions of the substrate. The laser irradiation selectively heats only the region containing boron dopants (BSF region) to the required activation temperature, while the rest of the substrate remains at lower temperatures, preserving its lifetime and preventing bulk degradation.
Solution Approach 2:
The thermal activation process is segmented in space rather than applied uniformly. The laser energy is concentrated on specific zones requiring dopant activation, creating a spatially differentiated thermal field that activates boron locally without subjecting the entire substrate to damaging high temperatures.
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 approach minimizes manufacturing constraints by enabling simultaneous implantation and activation under vacuum, reducing contamination risks, and preventing substrate degradation, while achieving effective doping without excessive heating.
Implementation Method 1
at least the thermal activation of the first doping elements is carried out by laser irradiation
Implementation Method 2
thermal activation of the first doping elements implanted at a first activation temperature
Implementation Method 3
implantation of first doping elements in the thickness of the substrate
Data Source
Figure 1~6
AI summary
This process for manufacturing a photovoltaic cell consists in: producing a semiconductor substrate (10) comprising first and second opposite sides (12, 16); producing, in the first side (12) of the substrate (10), a first semiconductor zone (14) doped by implanting first dopant elements into the thickness of the substrate and by thermally activating the first implanted dopant elements at a first activation temperature; and producing, on the second side (16) of the substrate (10), a second semiconductor zone (18) by implanting second dopant elements into the thickness of the substrate and by thermally activating the second implanted dopant elements at a second activation temperature that is below the first activation temperature. The substrate is more than 50 microns in thickness and at least the thermal activation of the first dopant elements is carried out by laser irradiation, the irradiation parameters being chosen so that the radiation is absorbed at most in a depth of the first micron of the substrate.