Co-diffusion of Boron and Phosphorus in Silicon Solar Cells
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Solution Overview
Problem
The existing methods for manufacturing solar cells using both Boron and Phosphorous diffusion face challenges such as increased series resistance due to Boron diffusion out of the protective layer, edge compensation issues, and high costs associated with wafer cutting, particularly when Phosphorous diffusion is performed before Boron diffusion.
Innovation Solution
Stabilizing and reducing effused Phosphorous during the Boron diffusion process by pre-diffusing Phosphorous into the substrate surface, allowing for the removal of the Phosphorous diffusion source before Boron diffusion, which improves the quality and reproducibility of the Boron-diffused p-type emitter and avoids shunting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Phosphorous diffusion is performed before Boron diffusion, then the Phosphorous-diffused side can be protected from Boron during Boron diffusion, but Phosphorous effuses from the Phosphorous-diffused layer at Boron diffusion temperature and diffuses into the Boron-side, hampering the quality of the Boron-doped emitter
Solution Approach 1:
The patent applies preliminary action by performing a first Phosphorous diffusion step before the Boron diffusion step. This pre-diffusion of Phosphorous into the substrate creates a stabilized Phosphorous-diffused layer that prevents Phosphorous effusion during subsequent high-temperature Boron diffusion, thereby protecting the quality of the Boron-doped emitter while maintaining protection of the Phosphorous-diffused side
2Reliability
If a protective layer is used to block Phosphorous from diffusing into the Boron-diffused side, then Phosphorous diffusion is blocked, but Boron diffuses out from the Boron-diffused layer to the protective layer and is depleted near the interface, increasing sheet resistance and series resistance
Solution Approach 1:
The patent extracts and removes the protective layer after the Phosphorous pre-diffusion step. By removing the protective layer before Boron diffusion, Boron can diffuse uniformly into the substrate without being depleted at the interface, thereby maintaining low sheet resistance and series resistance while the previously established Phosphorous-diffused layer continues to provide protection
3Manufacturing precision
If separate diffusions for Boron and Phosphorous are used with wafers placed together in pairs, then compensation of Boron by Phosphorous is limited to wafer edges, but wafer edges must be cut off which significantly increases costs per Wp produced
Solution Approach 1:
The patent applies local quality by performing sequential diffusion steps on the same wafer surface. The first Phosphorous diffusion creates a localized Phosphorous-diffused layer at specific regions, followed by Boron diffusion that selectively dopes other regions. This sequential approach eliminates the need for wafer pairing and edge cutting, thereby reducing manufacturing costs while maintaining precise doping control
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 enhances the quality and reproducibility of the Boron-diffused emitter, reduces series resistance, and prevents the creation of an n-type edge on the Boron-diffused side, resulting in improved solar cell performance and efficiency.
Implementation Method 1
Phosphorous diffuses faster and is more soluble in Silicon... the amount of the effused Phosphorous from the diffusion source is larger and more fluctuating than that from the Silicon surface where Phosphorous is already diffused-in
Implementation Method 2
the higher temperature Boron-diffusion step is usually processed before the lower temperature Phosphorous-diffusion step
Implementation Method 3
Phosphorous is effused from the Phosphorous-diffused layer at the temperature of the Boron diffusion
Data Source
Figure 1~3d
Figure 4a~4f
Figure 5a~5d
AI summary
The present invention provides a method of manufacturing a crystalline silicon solar cell, subsequently comprising: - providing a crystalline silicon substrate having a first side and a second side opposite the first side; - pre-diffusing Phosphorus into a first side of the substrate to render a Phosphorus diffused layer having an initial depth; - blocking the first side of the substrate; - exposing a second side of the substrate to a Boron diffusion source; - heating the substrate for a certain period of time and to a certain temperature so as to diffuse Boron into the second side of the substrate and to simultaneously diffuse the Phosphorus further into the substrate.