Double-doped Photovoltaic Cell Heterojunction
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Solution Overview
Problem
Heterojunction photovoltaic cells with amorphous/crystalline structures face challenges in reducing surface state density and recombination rates at interfaces, which affect photoelectric conversion efficiency and fill factor, due to impurities and complex layer deposition processes.
Innovation Solution
A photovoltaic cell structure with a crystalline semiconductor substrate and amorphous layers of specific doping levels, including a microdoped layer directly deposited on the substrate, reduces surface state density and recombination rates, and improves fill factor by gradient or constant doping profiles in the layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a heavily doped amorphous layer is directly deposited on the crystalline substrate to create BSF field, then carrier separation is improved, but surface state density increases and recombination rate increases
Solution Approach 1:
The heavily doped amorphous layer is segmented into multiple sub-layers with different doping concentrations. The layer adjacent to the crystalline substrate has lower doping concentration to reduce surface states, while deeper layers have higher doping concentrations to maintain BSF field effect, thus resolving the contradiction between carrier separation and recombination reduction.
Solution Approach 2:
Different regions of the amorphous layer are assigned different doping qualities: the interface region near the substrate uses low doping to minimize surface states and recombination, while the bulk region uses high doping to create strong electric field for carrier separation, achieving local optimization of both functions.
2Power
If multiple separate amorphous layers are deposited to compensate for parasitic doping, then open circuit voltage is improved, but device complexity increases
Solution Approach 1:
Multiple amorphous layers with different doping concentrations are merged into a single continuously doped amorphous layer with a doping gradient. This integration maintains the voltage improvement benefits of multiple layers while simplifying the deposition process into a single continuous operation, reducing device complexity.
Solution Approach 2:
The doping concentration parameter is continuously varied within the single amorphous layer to create a gradient profile, transitioning from low doping at the substrate interface to high doping in the bulk. This parameter variation achieves the electrical properties of multiple discrete layers within a unified structure.
3Power
If dopant is added at the amorphous/crystalline interface to passivate surface states, then open circuit voltage is improved, but manufacturing precision becomes difficult to control
Solution Approach 1:
Instead of adding discrete dopant quantities at the interface, the doping concentration is continuously varied as a gradient parameter throughout the amorphous layer. This continuous parameter approach is more easily controlled during deposition than discrete dopant addition, improving manufacturing precision while maintaining surface passivation effects.
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 proposed structure achieves a low carrier recombination rate, high open-circuit voltage, and enhanced fill factor by minimizing surface states and series resistance, while simplifying the layer deposition process.
Implementation Method 1
a first amorphous layer, on a first face of the substrate, of the same semiconductor material and of a second type of conductivity, opposite to the first and having a doping level of between 1.10 19 and 1.10 21 atoms per cm3
Implementation Method 2
A photovoltaic cell is generally based on a junction between a P-type semiconductor and an N-type semiconductor. It is recalled that in such a cell the incident photons generate in the semiconductor electron-hole pairs then separated by the electric field present in the space charge region.
Implementation Method 3
the incident photons generate in the semiconductor electron-hole pairs then separated by the electric field present in the space charge region
Implementation Method 4
The doping within the first and second layers is gradual, the doping level increasing in a direction going from the second layer towards the first layer
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
The invention relates to a photovoltaic cell comprising a heterojunction between a crystalline semiconductor substrate (210) of a first type of conductivity and a first amorphous layer (220) of the same semiconductor material, of a second type of conductivity, opposite to the first and having a doping level between 1 x 10¹⁹ and 1 x 10²² atoms/cm³. The photovoltaic cell further comprises a second amorphous layer (225) of the same type of conductivity as the first layer and having a doping level between 1 x 10¹⁶ and 1 x 10¹⁸ atoms/cm³, said second layer being deposited directly on a first face of the substrate and being covered by said first layer. The cell finally comprises, on a second face of the substrate opposite the first face, a third amorphous layer (260), of the same material as the substrate and of the same type of conductivity, with a doping level between 1.1019 and 1.1022 atoms/cm3