Back-Side Contact Solar Cell With Laser-Defined Selective Contacts
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Solution Overview
Problem
The production of back-contact solar cells with high efficiency is complex due to the need for precise masking and structuring steps to achieve fine resolution of selective contacts, which can lead to increased series resistance and recombination losses.
Innovation Solution
A method for producing back-side-contacted solar cells using a semiconductor substrate with a tunnel layer and highly doped silicon layers, where the highly doped base regions are selectively overcompensated, allowing for mask-free fine structuring by local laser irradiation, and the use of a precursor layer to achieve efficient doping without excessive dopant concentration, reducing recombination and series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If masking and structuring steps are used to create fine resolution selective contacts, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the masking step from the manufacturing process by using direct laser irradiation to define the selective contact regions. The laser directly writes the fine structures without requiring physical masks, thereby simplifying the device complexity while maintaining manufacturing precision.
Solution Approach 2:
The patent replaces the mechanical masking system with an optical laser writing system. Instead of using physical masks that require precise alignment and handling, the invention uses laser irradiation to directly create the fine resolution structures, substituting a mechanical process with an optical one that is inherently more precise and simpler.
2Reliability
If dopant concentration is increased to reduce series resistance, then electrical conductivity is improved, but recombination losses increase
Solution Approach 1:
The patent applies local quality by creating selectively doped regions where dopant concentration is high only in specific areas where it is needed for low series resistance, while other regions maintain lower dopant concentrations to minimize recombination. The laser irradiation selectively activates doping in contact regions while leaving other areas with optimal lower doping levels.
Solution Approach 2:
The patent changes the doping parameter spatially and selectively through laser irradiation. By controlling the laser parameters (power, duration, scanning speed), the invention achieves different dopant concentrations in different regions, optimizing both series resistance and recombination losses through localized parameter adjustment.
3Loss of energy
If contact area is minimized to reduce interfacial recombination, then recombination losses are reduced, but series resistance increases
Solution Approach 1:
The patent applies local quality by creating highly doped regions precisely at the contact interfaces where low resistance is needed, while maintaining minimal contact area to reduce interfacial recombination. The selective laser doping ensures that the small contact areas have locally optimized high dopant concentrations that provide low resistance despite the reduced area.
Solution Approach 2:
The patent changes the dopant concentration parameter locally at the contact interfaces through selective laser irradiation. This creates a steep doping gradient where the contact regions have very high dopant concentrations (reducing resistance) while the bulk material maintains lower concentrations (reducing recombination), effectively decoupling the two competing requirements.
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 efficiency of solar cells by minimizing recombination and series resistance, achieving higher efficiency without the complexity of traditional masking steps, while maintaining low contact resistance and precise doping control.
Implementation Method 1
a pulsed laser beam drives two different dopants, e.g., boron and phosphorus, into the silicon by melting the surface separately in time and space
Implementation Method 2
by melting the surface separately in time and space, creating either a high p-type or n-type doping concentration
Implementation Method 3
This tunnel oxide passivates the silicon surface but is simultaneously thin enough to allow electrons, depending on their polarity, to tunnel from the semiconductor to the electrode through the oxide
Implementation Method 4
To excite electron tunneling, an electric field must be present at the tunnel oxide. This electric field can be generated by a highly doped n- or p-type silicon on the tunnel oxide
Implementation Method 5
In highly doped n-type silicon, only electrons pass through the tunnel oxide, also known as electron flow
Implementation Method 6
in highly doped p-type silicon, only a so-called hole flow occurs: electrons move from the highly doped p-type silicon into the silicon base
Implementation Method 7
The dopants from the phosphosilicate glass and the highly doped p-type silicon layer diffuse into the silicon melt at the back surface
Implementation Method 8
The energy of the laser radiation locally melts the phosphosilicate glass, the highly doped p-type silicon layer, the tunnel layer, and the back surface in selected areas
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
The invention relates to a back-side contact solar cell (10), comprising a semiconductor substrate (12), in particular a silicon wafer, comprising a front side (16) and a back side (14), wherein the solar cell (10) comprises, on the back side, electrodes (30) of a first polarity and electrodes (32) of a second polarity, wherein there is a tunnel layer (18) and a highly doped silicon layer (20) among the electrodes (34) of a first polarity, and the electrodes (36) of the second polarity directly and mechanically contact the semiconductor substrate (12).