Selective Emitter Photovoltaic Cell Annealing
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Solution Overview
Problem
Existing methods for manufacturing selective emitter photovoltaic cells face challenges due to incompatible steps in annealing and n-dopant diffusion, requiring specific energy inputs and leading to energy constraints and potential short-circuiting issues.
Innovation Solution
A method that simultaneously produces the n+ emitter, n contacts, and p contacts during a single annealing step, using an antireflection layer with n-type dopants and a chemical compound like ammonia to accelerate diffusion, allowing for deeper n++ emitter formation and avoiding short-circuiting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate steps are used for n-dopant diffusion and annealing, then doping precision can be controlled, but manufacturing complexity and energy consumption increase
Solution Approach 1:
The patent combines the n-dopant diffusion step and the annealing step into a single simultaneous processing operation. The annealing furnace serves dual purposes: forming the metallurgical contact between metal paste and silicon substrate, and diffusing n-type dopants from the silicon nitride layer into the substrate. This integration eliminates the need for separate diffusion and annealing equipment and process sequences, thereby reducing manufacturing complexity while maintaining doping precision through controlled dopant release during the annealing cycle.
2Reliability
If high doping rate is used in n-doping zones, then good ohmic contact is achieved, but Auger recombination increases reducing cell efficiency
Solution Approach 1:
The patent implements selective emitter technology where the n-type dopant concentration is spatially differentiated. The silicon nitride layer is deposited uniformly across the surface, but through selective removal (opening) of the layer in specific contact regions, high doping rates are achieved only in localized areas where metal contacts are applied. In the bulk emitter regions without metal contacts, the dopant concentration remains lower, minimizing Auger recombination losses. This local quality approach allows simultaneous optimization of contact quality and bulk recombination characteristics.
3Manufacturing precision
If multiple separate processing steps are used, then each step can be optimized independently, but total energy consumption increases
Solution Approach 1:
The patent merges the annealing process and n-dopant diffusion process into a single thermal processing step performed in one furnace cycle. The annealing furnace, which would otherwise be used solely for contact formation, simultaneously performs dopant diffusion by releasing phosphorus atoms from the silicon nitride layer into the silicon substrate during the high-temperature treatment. This eliminates the need for a separate diffusion furnace and process, reducing total energy consumption while maintaining the ability to optimize contact properties and doping profiles through coordinated process parameters.
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 approach reduces energy constraints and achieves a high-quality n+ emitter with Voc > 620 mV, ensuring good ohmic contact and passivation while preventing short-circuiting, thus improving photovoltaic cell efficiency.
Implementation Method 1
a chemical compound making it possible to accelerate the diffusion of the n-type doping atoms in the silicon substrate
Implementation Method 2
annealing of the pastes (silver and aluminum) in a continuous furnace, for example at a temperature of 885°C
Data Source
Figure 1A~1F
Figure 2A~2E
AI summary
The process according to the invention comprises the following steps: depositing an antireflection layer (7) containing n-type dopants on a p-type or n-type silicon substrate (1), said deposition being carried out in the presence of a chemical compound that accelerates diffusion of the n-type dopant atoms into said substrate (1); overdoping at least one zone of the substrate (1), so as to produce at least one overdoped n++ emitter (6), by diffusing, in specific locations, the n-type dopants from at least one zone of the antireflection layer (7); depositing at least one n-type conductive material (3) on the at least one overdoped n++ emitter (6) and at least one p-type conductive material (4) on the side of the substrate (1) opposite that comprising the antireflection layer (7); and producing n-type contacts (3) and p-type contacts (4) at the same time as an n+ emitter (5) by way of an anneal able to make n-type dopants diffuse into the substrate from the antireflection layer (7).