Transition Metal Layer Sodium Diffusion Control
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Solution Overview
Problem
Existing thin-film solar cells face challenges in controlling sodium diffusion and achieving high efficiency, particularly when using substrates other than glass, as they do not provide a readily available supply of sodium, which is crucial for enhancing p-type conductivity and open circuit voltage.
Innovation Solution
A solar cell design incorporating a first transition metal layer with molybdenum, an alkali element or compound, and a lattice distortion element, such as oxygen, to diffuse sodium into a copper indium selenide-based alloy absorber layer, with a second transition metal layer allowing controlled alkali diffusion and an optional alkali diffusion barrier layer to manage sodium distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass substrates are used to provide sodium supply, then p-type conductivity and open circuit voltage are enhanced, but device complexity and manufacturing flexibility are reduced due to substrate dependency
Solution Approach 1:
The invention extracts the sodium supply function from the substrate and relocates it to the first transition metal layer. This allows non-glass substrates to be used while still providing the necessary sodium for enhancing p-type conductivity and open circuit voltage in the CIS-based absorber layer.
Solution Approach 2:
The first transition metal layer acts as an intermediary between the substrate and the absorber layer, providing sodium diffusion control. This intermediary layer enables the use of various substrate materials while maintaining the required sodium supply for high-performance photovoltaic operation.
2Reliability
If sodium diffusion is increased to enhance conductivity, then open circuit voltage improves, but uncontrolled diffusion degrades manufacturing precision and efficiency
Solution Approach 1:
The invention segments the transition metal layer into two distinct layers: the first transition metal layer containing alkali elements for sodium supply, and the second transition metal layer with higher porosity for controlled diffusion. This segmentation enables precise control over sodium concentration in the absorber layer while achieving the desired open circuit voltage enhancement.
Solution Approach 2:
Different regions of the transition metal structure are assigned different properties: the first layer provides sodium reservoir function with specific composition, while the second layer provides controlled diffusion pathways with higher porosity. This local differentiation enables precise sodium concentration control in the absorber layer.
3Productivity
If transition metal layers with alkali elements are used to enable sodium diffusion, then efficiency increases, but device complexity increases due to additional layers and processes
Solution Approach 1:
The first transition metal layer performs multiple functions: it serves as a sodium reservoir, provides lattice distortion through oxygen incorporation, and acts as a diffusion barrier layer. This multi-functionality reduces the need for separate dedicated layers, thereby limiting the increase in device complexity while achieving high efficiency through controlled sodium diffusion.
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 design enhances the p-type conductivity and efficiency of the solar cell, achieving efficiencies up to 11.3%, compared to 5.4% without sodium doping, by precisely controlling sodium concentration and diffusion, thereby improving the overall performance.
Implementation Method 1
0.005 to 1.5 atomic percent sodium diffused from the first transition metal layer
Implementation Method 2
a lattice distortion element or a lattice distortion compound selected from the group consisting of oxygen, MoO2 and MoO3
Data Source
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AI summary
A solar cell includes a substrate, a first electrode located over the substrate, where the first electrode comprises a first transition metal layer, at least one p-type semiconductor absorber layer located over the first electrode, an n-type semiconductor layer located over the p-type semiconductor absorber layer, and a second electrode located over the n-type semiconductor layer. The first transition metal layer contains (i) an alkali element or an alkali compound and (ii) a lattice distortion element or a lattice distortion compound. The p-type semiconductor absorber layer includes a copper indium selenide (CIS) based alloy material.