PERC Tandem Solar Cell Sacrificial AlOx Passivation Interface
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Solution Overview
Problem
Tandem solar cell devices with Passivated Emitter and Rear Contact (PERC)-based bottom cells face issues such as enhanced carrier recombination at the interface and increased series resistance due to contamination and electrical resistance, leading to reduced efficiency and increased manufacturing costs.
Innovation Solution
A method involving a silicon-based bottom solar cell with a carrier extracting layer stack and a passivating AlOx layer, where a sacrificial AlOx layer is used for hydrogenation and passivation, and a single all-sided deposition process for AlOx layers at both surfaces to simplify manufacturing and reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin oxide layer is formed on the emitter during bottom cell processing, then passivation is improved, but electrical resistance increases and carrier recombination is enhanced
Solution Approach 1:
The patent changes the chemical composition and thickness parameters of the oxide layer by introducing a sacrificial Al2O3 layer that is selectively removed. This transforms the permanent thin oxide (harmful) into a temporary processing aid that enables better passivation without the harmful resistance effects
Solution Approach 2:
The harmful thin oxide layer is completely removed by extracting it through selective etching of the sacrificial Al2O3 layer. This extraction eliminates the electrical resistance problem while the passivation benefits are retained through alternative means (interface engineering)
2Reliability
If additional process steps are added for front passivation or protection against surface oxides, then passivation quality is improved, but manufacturing time and cost increase
Solution Approach 1:
The patent merges the sacrificial layer deposition with the existing ALD process used for rear surface passivation. Both front and rear Al2O3 layers are deposited in a single all-sided deposition process, eliminating the need for separate front surface protection steps and reducing manufacturing complexity
Solution Approach 2:
The ALD deposition process is made universal by applying it to both front and rear surfaces simultaneously. The same process equipment and chemistry are used for both surfaces, maximizing equipment utilization and simplifying the manufacturing workflow
3Reliability
If the sacrificial AlOx layer is used for hydrogenation and passivation, then carrier recombination is reduced, but an additional deposition and removal step is required
Solution Approach 1:
The sacrificial Al2O3 layer serves multiple functions automatically: it provides hydrogenation during deposition, maintains passivation during rear contact processing, and is selectively removed to reveal the improved emitter interface. The layer essentially services the process itself without requiring external intervention
Solution Approach 2:
The sacrificial layer is deposited in advance before rear contact processing. This preliminary action ensures the emitter interface is protected and hydrogenated before any subsequent processing that might expose it to damage or contamination
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 carrier recombination, simplifies manufacturing, and lowers material requirements and costs, enhancing the efficiency of the tandem solar cell device by improving the passivation and hydrogenation of the emitter layer.
Implementation Method 1
Creation of rear electrical contacts implies the second AlOx is subject to a thermal annealing promoting hydrogenation
Implementation Method 2
deposition of an AlOx layer at the rear surface of the substrate allows to simplify manufacturing; the two layers may be deposited within a single all-sided deposition process
Implementation Method 3
The second layer AlOx is removed from the emitter layer on the front surface by means of a single-sided etching process
Data Source
AI summary
A method for manufacturing a two terminal or three terminal tandem solar cell comprising a silicon-based bottom solar cell and a thin-film top solar cell; the method comprising: providing a silicon substrate with a front surface and a rear surface, carrying out a sequence of steps comprising:creating on the front surface a carrier extracting layer stack comprising at least a carrier extracting layer formed on or in the front surface of the substrate, creating on the rear surface a passivating coating layer comprising deposition of a first AlOx layer, creating sacrificial layer stack comprising a second AlOx layer on the carrier extracting layer stack on the front surface; creating metal-based electrical contacts on the rear surface, including an annealing step; removing the sacrificial layer stack from the carrier extracting layer stack, and creating the thin film top solar cell on the carrier extracting layer stack.