Floating Junction Front Surface Field for Interdigitated Back Contact Solar Cells
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Solution Overview
Problem
Inter-digitated back-contact solar cells face absorption loss due to the presence of intrinsic and doped a-Si:H materials at the front surface, which reduces short circuit current and efficiency due to strong light absorption and high minority carrier recombination in these materials.
Innovation Solution
A photovoltaic device with a front surface field structure comprising a crystalline layer and a noncrystalline layer, both doped with opposite conductivity types to the substrate, forming a floating p-n junction that repels majority carriers and reduces carrier recombination, replacing the intrinsic a-Si:H layer to minimize absorption loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intrinsic and doped a-Si:H layers are used to form the front surface field junction, then passivation and electric field formation are improved, but absorption loss increases due to strong light absorption in these materials
Solution Approach 1:
The patent extracts and removes the intrinsic a-Si:H layer from the front surface field junction structure, retaining only the doped a-Si:H layer. This extraction eliminates the source of strong light absorption while preserving the necessary passivation and electric field formation functions provided by the doped layer.
Solution Approach 2:
The patent changes the optical parameter of the front surface field junction by replacing the intrinsic layer with a doped layer, which has different optical absorption characteristics. This parameter change reduces light absorption loss while maintaining the electrical functionality of the junction.
2Reliability
If intrinsic and doped a-Si:H layers are used to form the front surface field junction, then carrier repulsion is improved, but minority carrier recombination increases due to high defect density in these materials
Solution Approach 1:
The patent extracts and removes the intrinsic a-Si:H layer that contains high defect density, which is the source of minority carrier recombination. The doped a-Si:H layer is retained as it provides the necessary carrier repulsion function with lower recombination losses.
3Loss of energy
If the doped a-Si:H layer is omitted, then absorption loss is reduced, but carrier repulsion at the front surface deteriorates
Solution Approach 1:
The patent uses the doped a-Si:H layer as an intermediary that performs multiple functions: it provides carrier repulsion through its electric field while having reduced light absorption compared to the intrinsic layer. This intermediary layer mediates between the conflicting requirements of carrier repulsion and absorption minimization.
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 solution enhances short circuit current and efficiency by reducing absorption loss and carrier recombination, while maintaining effective passivation and flexibility in selecting materials for the anti-reflection coating layer.
Implementation Method 1
A floating p-n junction is formed at an interface between the crystalline layer and the substrate, the p-n junction being configured to repel majority carriers from a front surface
Implementation Method 2
Methods for forming an interdigitated back contact heterojunction photovoltaic device
Data Source
AI summary
A photovoltaic device includes a crystalline substrate having a first dopant conductivity, an interdigitated back contact and a front surface field structure. The front surface field structure includes a crystalline layer formed on the substrate and a noncrystalline layer formed on the crystalline layer. The crystalline layer and the noncrystalline layer are doped with dopants having an opposite dopant conductivity from that of the substrate. Methods are also disclosed.