TOPCon Solar Cell Selective Emitter for Shorter Boron Diffusion
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Solution Overview
Problem
N-type TOPCon solar cells face challenges with boron doping, requiring high temperatures and long times to achieve optimal junction depth, leading to high manufacturing costs and energy consumption due to the need for high-quality silicon wafers and inefficient metal contact recombination.
Innovation Solution
A selective emitter structure with a first emitter layer having a smaller junction depth and lower boron doping than a second emitter region, combined with a tunnel passivation structure and anti-reflection films, reduces the high-temperature boron diffusion time and improves optical response, while maintaining photoelectric conversion performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron doping is performed to achieve a junction depth above 0.7 μm for optimal metal contact recombination, then metal contact recombination is reduced, but the high-temperature doping time exceeds 3 hours leading to high power consumption and manufacturing cost
Solution Approach 1:
The emitter structure is divided into two distinct regions: a first emitter layer with junction depth of 0.3-0.7 μm and a second emitter region with junction depth above 0.7 μm. This segmentation allows different portions of the emitter to serve different functions - the first layer optimizes optical response while the second region ensures low metal contact recombination, eliminating the need for uniform deep doping across the entire emitter.
Solution Approach 2:
Different regions of the emitter are doped with different boron concentrations and junction depths to optimize local performance. The first emitter layer has lower boron doping concentration and shallower junction depth for regions requiring good optical response, while the second emitter region has higher doping concentration and deeper junction depth for regions requiring low contact recombination. This local quality differentiation resolves the contradiction between deep doping requirements and manufacturing efficiency.
2Ease of manufacture
If uniform junction depth is used in the emitter structure, then manufacturing is simplified, but optical response and recombination rate are not optimal
Solution Approach 1:
The emitter is segmented into two regions with different doping characteristics. The first emitter layer provides optimal optical response with shallower junction depth, while the second emitter region ensures low contact recombination with deeper junction depth. This segmentation allows each region to be optimized for its specific function rather than using a compromise uniform design.
Solution Approach 2:
The emitter structure implements local quality by having different boron doping concentrations and junction depths in different regions. The first emitter layer has lower doping concentration for regions where optical response is critical, while the second emitter region has higher doping concentration for regions where electrical contact performance is critical. This resolves the contradiction between manufacturing simplicity and performance optimization.
3Length of stationary object
If high-temperature doping is performed for more than 3 hours to achieve deep junction, then desired junction depth is achieved, but power consumption and equipment loss increase significantly
Solution Approach 1:
The doping process is segmented into two stages creating two emitter regions with different junction depths. The first emitter layer is formed with moderate doping conditions achieving 0.3-0.7 μm depth, while the second emitter region is formed with more aggressive doping to achieve depth above 0.7 μm. This segmentation allows the overall structure to achieve deep junction benefits without requiring uniform deep doping across the entire emitter, thereby reducing total energy consumption.
Solution Approach 2:
Different regions of the emitter receive different doping treatments to achieve locally optimized junction depths. The first emitter layer receives lighter doping for optimal optical response, while the second emitter region receives heavier doping for low contact recombination. This local quality approach achieves the necessary deep junction characteristics only where required, reducing overall power consumption compared to uniform deep doping.
4Length of stationary object
If long-time high temperature doping is used to achieve deep junction, then boron diffusion is sufficient, but higher quality silicon wafers are required which increases levelized cost of energy
Solution Approach 1:
The emitter structure is segmented into two regions with different doping profiles. The first emitter layer with shallower junction depth (0.3-0.7 μm) and lower boron concentration can be achieved with less stringent wafer quality requirements, while the second emitter region with deeper junction depth (>0.7 μm) provides the necessary electrical performance. This segmentation reduces the overall quality requirements for the silicon wafer compared to uniform deep doping, thereby reducing manufacturing costs.
Solution Approach 2:
The doping structure implements local quality with different boron concentrations and junction depths in different regions. The first emitter layer has lower doping concentration suitable for regions where optical response is prioritized, while the second emitter region has higher doping concentration for regions where electrical contact is prioritized. This local differentiation reduces the need for uniformly high-quality wafers across the entire device, lowering manufacturing costs.
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 reduces manufacturing costs and energy consumption by shortening the boron diffusion process, enhancing optical response, and improving photoelectric conversion efficiency by optimizing junction depths and doping concentrations.
Implementation Method 1
TOPCon (Tunnel Oxide Passivated Contact) solar cell is a solar cell that uses an ultra-thin oxide layer as a passivation layer structure
Implementation Method 2
boron doping to form the emitter structure... boron atoms are difficult to dope, and it requires a temperature of more than 970 degrees and more than 3 hours to reach a junction depth of more than 0.7 μm
Implementation Method 3
N-type TOPCon cells... will gradually replace p-type cells to dominate the market
Data Source
AI summary
A method for preparing a solar cell is provided. The method includes providing a N-type silicon substrate; depositing a tunnel passivation structure on the first surface of the N-type silicon substrate, and then depositing a mask layer on the tunnel passivation structure; cleaning the second surface of the N-type silicon substrate; performing boron diffusion treatment on the cleaned second surface of the N-type silicon substrate and annealing treatment on the tunnel passivation structure in the same environment, so that a first emitter layer is formed on the second surface of the N-type silicon substrate and the tunnel passivation structure is crystallized; performing laser patterning treatment on the first emitter layer to form a second emitter region; depositing a passivation and anti-reflection film; and forming a first electrode and a second electrode.