Photovoltaic Cell Passivation Stack for N-Type and P-Type Surfaces
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Solution Overview
Problem
Silicon-based photovoltaic cells face performance limitations due to surface recombination of charge carriers, with existing passivation materials often inducing band-bending that is either ineffective or detrimental for n-type semiconductor surfaces, and lacking a balance between effective excess carrier lifetime, fixed charge density, and interface state density.
Innovation Solution
A photovoltaic cell with a passivation layer stack comprising a POx- and Al-comprising-layer, which includes a mixture of phosphorus, aluminium, and oxygen, tailored to achieve optimal balance between effective excess carrier lifetime, fixed charge density, and interface state density, and optionally capped with an Al2O3 layer for 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 passivation of p-type surfaces is improved, but passivation of n-type surfaces deteriorates due to upward band-bending and inversion layer formation
Solution Approach 1:
The patent employs a composite passivation structure consisting of a POx-layer (providing positive charge for n-type surface passivation) combined with an Al2O3-layer (providing negative charge for p-type surface passivation). This composite approach allows a single passivation system to effectively passivate both n-type and p-type semiconductor surfaces by combining the benefits of both positively and negatively charged materials.
2Reliability
If silicon nitride is used for n-type surface passivation, then downward band-bending is achieved, but the charge concentration is insufficient compared to aluminium oxide
Solution Approach 1:
The patent modifies the charge concentration parameter by using a POx-layer which provides a high positive charge concentration (>5×1012 cm−2), significantly exceeding the charge concentration of conventional silicon nitride films. This parameter change enables strong downward band-bending and effective passivation of n-type surfaces without the limitations of silicon nitride.
3Reliability
If passivation layers are deposited to reduce surface recombination, then energy conversion efficiency is improved, but the complexity of the manufacturing process increases
Solution Approach 1:
The patent divides the passivation function into two separate layers with distinct roles: the POx-layer provides positive charge for n-type surface passivation and the Al2O3-layer provides negative charge for p-type surface passivation. This segmentation allows each layer to be optimized for its specific function while together providing universal passivation capability for both n-type and p-type surfaces.
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 provides effective passivation for both n-type and p-type surfaces, enhancing energy conversion efficiency by reducing surface recombination, and the capping layer ensures chemical stability and optimal performance.
Implementation Method 1
this layer or stack also induces band bending at the semiconductor surface, such that the surface concentration of one type of charge carrier (either electrons or holes) is reduced
Implementation Method 2
the surface must be passivated such that the recombination activity of the surface states is suppressed
Implementation Method 3
the capping layer structure ensures chemical stability and optimal performance
Data Source
AI summary
A photovoltaic cell includes a silicon substrate having two opposite main surfaces. A first main surface of the two main surfaces is covered with a passivation layer stack, including a POx- and Al-including-layer covering the first main surface, and a capping layer which covers the POx- and Al-including-layer. A method for manufacturing a photovoltaic cell is also disclosed.