Bifacial Photovoltaic Cell Boron Diffusion Control
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Solution Overview
Problem
Bifacial photovoltaic cell fabrication faces challenges in achieving high efficiency due to boron diffusion-associated degradation and edge shunting, which limits the conversion of sunlight into electricity, and existing methods are complex and inefficient.
Innovation Solution
A method involving the formation of a boron-containing layer on a silicon substrate with a cap layer to control boron doping, followed by simultaneous phosphorous deposition and diffusion in a POCl3 atmosphere, reducing boron diffusion and preventing cross-doping, thereby enhancing the efficiency and shunt resistance of bifacial cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron is used as a p-dopant to reduce back surface recombination, then back surface recombination is reduced and efficiency is improved, but bulk lifetime is degraded
Solution Approach 1:
The patent applies local quality by creating a localized p+ layer at the back surface using boron doping, while keeping the bulk region unaffected. The boron-containing layer is deposited only on the back surface and diffuses locally to form a p+ region, reducing back surface recombination without introducing harmful boron into the bulk where it would degrade lifetime.
Solution Approach 2:
The patent uses a preliminary protective action by applying a cap layer (such as silicon nitride or silicon oxide) before boron diffusion. This cap layer prevents excessive boron diffusion into the bulk and controls the doping profile, ensuring boron stays confined to the surface region where it is needed, thus protecting the bulk lifetime while still achieving back surface recombination reduction.
2Ease of manufacture
If gas phase processes are used for dopant deposition, then doping is achieved, but cross-doping of inappropriate regions occurs
Solution Approach 1:
The patent segments the doping process by treating the front and back surfaces separately. The back surface is doped with boron through a cap layer, while the front surface receives phosphorus doping. This segmentation prevents cross-doping by spatially separating the dopant sources and deposition processes, ensuring each region receives only its intended dopant.
Solution Approach 2:
The cap layer serves as an intermediary that controls the boron diffusion process. It acts as a barrier that allows controlled diffusion of boron to the silicon surface while preventing boron from reaching inappropriate regions. This intermediary layer ensures manufacturing precision by confining the dopant to the intended region.
3Manufacturing precision
If protective layers and etching steps are added to prevent cross-doping, then doping precision is improved, but fabrication complexity increases
Solution Approach 1:
The patent merges multiple functions into the cap layer: it serves as a protective layer, a diffusion barrier, and a process simplifier. By combining these functions into a single layer, the patent achieves precise doping region control without adding multiple separate protective layers and etching steps, thus reducing fabrication complexity while maintaining manufacturing precision.
Solution Approach 2:
The cap layer exhibits multi-functionality by simultaneously providing protection during processing, controlling dopant diffusion, and preventing cross-doping. This universal layer performs multiple critical functions that would otherwise require separate process steps, thereby simplifying the overall fabrication process while maintaining high doping precision.
4Duration of action of moving object
If aluminum is used as a p-dopant to avoid bulk lifetime degradation, then bulk lifetime is maintained, but back surface recombination reduction is less effective
Solution Approach 1:
The patent applies local quality by using boron specifically at the back surface where its high solubility and effectiveness at reducing recombination are needed, while using aluminum or no doping in the bulk region where lifetime must be maintained. This localized application of boron achieves the desired back surface recombination reduction without the harmful effects of bulk boron doping.
Solution Approach 2:
The patent changes the doping parameter by using boron at the back surface with controlled concentration and depth through the cap layer process. By adjusting the boron concentration and diffusion depth parameters, the patent achieves optimal back surface recombination reduction while keeping bulk lifetime intact, effectively tuning the doping parameters to resolve the contradiction.
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 results in bifacial photovoltaic cells with improved efficiency, reduced boron concentrations, and increased shunt resistance, enabling higher energy generation per unit area while simplifying the fabrication process.
Implementation Method 1
diffusion of the boron from the boron-containing layer into the semiconductor substrate
Implementation Method 2
deposition of a phosphorous-containing layer on a first surface of the substrate, using POCl3 vapors as a component of gaseous phase surrounding the substrate
Implementation Method 3
phosphorous diffusion from the phosphorous-containing layer into the substrate to form an n-doped layer
Data Source
AI summary
A method of producing a bifacial photovoltaic cell is disclosed herein, the method comprising: forming a boron-containing layer on a second surface of a semiconductor substrate; forming a cap layer above the boron-containing layer; effecting simultaneously: i) deposition on the first surface and ii) diffusion into it of the phosphorous using POCl3 gas phase process and iii) diffusion of the boron into the second surface of the substrate, to thereby dope the first surface with n-dopant and the second surface with boron.