Silicon PV Passivation Stack for p-Type and n-Type Surfaces
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Solution Overview
Problem
The performance of silicon-based photovoltaic cells is limited by surface recombination of charge carriers due to surface states, which reduces energy conversion efficiency. Existing passivation materials often induce upward band-bending, which is advantageous for p-type surfaces but detrimental for n-type surfaces, creating a gap in effective passivation materials with strong positive or negative charge states.
Innovation Solution
A passivation layer stack comprising a POx- and Al-comprising-layer, which includes a mixture of phosphorus, aluminium, and oxide, is applied to the silicon substrate. This layer is tailored to achieve an optimal balance between effective excess carrier lifetime, fixed charge density, and interface state density, and is capped with an Al2O3 layer to provide chemical stability and moisture barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If negatively charged passivation materials (e.g., aluminium oxide) are used, then upward band-bending is induced which is advantageous for p-type surface passivation, but downward band-bending is required for n-type surface passivation
Solution Approach 1:
The passivation system is divided into two distinct layers: a first passivation layer containing negatively charged states (e.g., aluminium oxide) for p-type surface passivation, and a second passivation layer containing positively charged states (e.g., silicon oxide, silicon nitride) for n-type surface passivation. This segmentation allows each layer to be optimized for its specific function while working together to provide universal passivation capability.
Solution Approach 2:
The invention uses a composite passivation structure combining multiple materials with different charge characteristics. The first layer (aluminium oxide) provides strong negative charge for hole accumulation and p-type passivation, while the second layer (silicon oxide or silicon nitride) provides positive charge for electron accumulation and n-type passivation. This composite approach creates a versatile passivation system that adapts to different semiconductor types.
2Device complexity
If a single passivation material is used, then the structure is simple, but it cannot provide both upward and downward band-bending for different surface types
Solution Approach 1:
The passivation function is segmented into two separate layers, each with distinct charge characteristics. The first layer contains negatively charged states for p-type surfaces, while the second layer contains positively charged states for n-type surfaces. This segmentation resolves the contradiction by making the structure slightly more complex while dramatically improving versatility.
Solution Approach 2:
The two-layer passivation structure achieves universality by being able to passivate both p-type and n-type semiconductor surfaces effectively. The first layer handles p-type passivation through negative charge, while the second layer handles n-type passivation through positive charge, making the overall structure applicable to a wide range of semiconductor devices.
3Reliability
If aluminium oxide is used for p-type passivation, then effective passivation is achieved, but no material provides equivalent strong positive charge for n-type passivation
Solution Approach 1:
The passivation charge states are segmented into two separate layers with opposite charge polarities. The first layer concentrates negative charge states (comparable to aluminium oxide's effectiveness) for p-type surfaces, while the second layer concentrates positive charge states (using materials like silicon nitride) for n-type surfaces. This segmentation allows each layer to achieve high charge density optimized for its specific carrier type.
Solution Approach 2:
The invention changes the charge state parameter by using different materials with opposite charge characteristics in different layers. The first layer uses materials with negative charge states (aluminium oxide) while the second layer uses materials with positive charge states (silicon oxide, silicon nitride), effectively doubling the range of available charge densities for different passivation needs.
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
The POx- and Al-comprising-layer effectively passivates both p-type and n-type silicon surfaces by tailoring the atomic percentage ratio of phosphorus to phosphorus plus aluminium, resulting in improved excess carrier lifetime, reduced interface state density, and appropriate fixed charge density, leading to enhanced photovoltaic cell efficiency.
Implementation Method 1
the surface must be passivated such that the recombination activity of the surface states is suppressed
Implementation Method 2
this layer or stack also induces band bending at the semiconductor surface, such that the surface concentration of one type of charge carrier is reduced
Implementation Method 3
both contain positive charge states... aluminium oxide, which both provides effective passivation of p-type surfaces due to its large negative charge
Implementation Method 4
capped with an Al2O3 layer to provide chemical stability and moisture barrier properties
Implementation Method 5
Photovoltaic cells with passivation layers... limiting factor in the performance of silicon based photovoltaic cells... recombination of charge carriers at the surface
Data Source
Figure 1
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Figure 3a~3b
AI summary
A photovoltaic cell is disclosed comprising a silicon substrate having two opposite main surfaces, wherein a first main surface of the two main surfaces is covered with a passivation layer stack, comprising a POx- and Al- comprising-layer covering the first main surface, and a capping layer which covers the POx- and Al-comprising-layer. Also disclosed is a method for manufacturing a photovoltaic cell.