Selective Doping via Liquid Precursor for Solar Cell Junctions
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Solution Overview
Problem
Conventional solar cells face inefficiencies due to high surface recombination, high emitter dark current, poor lifetime, and poor spectral response, primarily because of the limitations in heavy phosphorous doping in the emitter region, which affects the formation of p-n junctions and contact resistance.
Innovation Solution
A method involving selective heavy and light doping of a silicon wafer using a doped liquid precursor, where the precursor is deposited and heated to create a doped film that diffuses dopants into the substrate, allowing for the formation of heavily and lightly diffused regions with varying sheet resistances, enabling improved contact resistance and reduced recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy phosphorous doping is applied in the emitter region to form metal contacts and reduce sheet resistance, then contact resistance is reduced and metal contact is achieved, but surface recombination increases, emitter dark current increases, and spectral response deteriorates
Solution Approach 1:
The patent applies different doping concentrations in different regions of the emitter: heavy doping (1E19 to 1E21 atoms/cm³) in contact regions under metal fingers for low contact resistance, and light doping (1E16 to 1E18 atoms/cm³) in non-contact regions for low surface recombination. This spatial variation in doping quality resolves the contradiction between achieving good metal contact and maintaining low surface recombination.
Solution Approach 2:
The emitter region is segmented into distinct zones: heavily doped contact regions and lightly doped non-contact regions. This segmentation allows each zone to be optimized for its specific function - contact regions for electrical connection and non-contact regions for carrier collection - thereby resolving the contradiction between contact resistance and surface recombination.
2Reliability
If heavy doping is applied throughout the emitter region to ensure low sheet resistance, then sheet resistance is reduced, but spectral response for light absorbed in the emitter deteriorates
Solution Approach 1:
The patent implements local quality variation by concentrating heavy doping only in contact regions where low sheet resistance is critical for electrical connection, while maintaining light doping in non-contact regions where spectral response is more important. This localized approach to doping quality resolves the contradiction between achieving low overall sheet resistance and maintaining good spectral response.
3Ease of manufacture
If uniform doping is applied to the emitter region, then the doping process is simple, but selective heavy doping under metal contacts and selective light doping in other regions cannot be achieved
Solution Approach 1:
The patent uses a photosensitive polymer mask as a preliminary structure that defines the doping pattern before the actual doping process. The mask is applied to the wafer surface, exposing only the regions where heavy doping is desired. This preliminary patterning action enables selective doping without requiring complex in-situ masking during the doping process itself, thus maintaining manufacturing simplicity while achieving doping versatility.
Solution Approach 2:
The photosensitive polymer acts as an intermediary between the doping source and the silicon substrate. It selectively allows dopant diffusion only in uncovered regions while blocking diffusion in masked areas. This intermediary mechanism enables precise spatial control of doping concentrations without directly complicating the doping process, resolving the contradiction between manufacturing ease and selective doping capability.
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 enhances the efficiency of solar cells by reducing surface recombination, emitter dark current, and improving spectral response, while allowing for the creation of high-low junctions and back surface fields, thereby increasing overall solar cell performance.
Implementation Method 1
The doped film is heated on the substrate wafer to diffuse the dopants from the doped film into the substrate wafer
Implementation Method 2
The doped liquid precursor is deposited on a surface of the substrate wafer to create a doped film on the surface of the substrate wafer
Data Source
AI summary
A method selectively diffuses dopants into a substrate wafer. The method comprises blanket depositing a doped liquid precursor including dopants on a surface of the substrate wafer to create a doped film on the surface of the substrate wafer, selectively forming a diffusion source in the doped film to selectively diffuse the dopants into the substrate wafer, and heating the doped film on the substrate wafer, wherein said heating the doped film diffuses the dopants from the doped film into the substrate wafer.