TOPCon Passivating Contact Stack for Uniform Dopant Diffusion
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Solution Overview
Problem
In mass production of tunnel oxide passivated contact (TOPCon) solar cells, the growth uniformity of the tunnel oxide layer and heavily doped polysilicon layer is difficult to control, leading to imbalanced process effects and reduced conversion efficiency.
Innovation Solution
A method is developed to form a passivating contact structure by alternately stacking polysilicon layers and doped layers, where the innermost and outermost layers are polysilicon layers, and the dopant concentration is adjusted to prevent diffusion into the tunnel layer, ensuring uniform dopant distribution and reduced contact resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tunnel oxide layer and heavily doped polysilicon layer are formed on the back of the cell, then good surface passivation is provided, but growth uniformity is difficult to control and process effects become imbalanced
Solution Approach 1:
The heavily doped polysilicon layer is segmented into multiple thin polysilicon sub-layers separated by undoped or lightly doped polysilicon layers. This segmentation allows each sub-layer to grow more uniformly and independently, preventing the formation of defects that would occur in a single thick doped layer, thereby improving growth uniformity while maintaining passivation quality.
Solution Approach 2:
Undoped or lightly doped polysilicon layers are introduced as intermediary layers between the tunnel oxide layer and heavily doped polysilicon layers. These intermediary layers act as buffers that prevent direct interaction between the tunnel oxide and heavily doped regions, reducing stress and improving the uniformity of layer growth while preserving the passivation function.
2Object-affected harmful factors
If dopant concentration is increased to improve contact properties, then contact resistivity decreases, but dopant diffusion into the tunnel layer increases causing degradation
Solution Approach 1:
The doped polysilicon layer is divided into multiple segments with alternating doped and undoped/lightly doped layers. This segmentation confines the dopant primarily within the doped sub-layers, preventing excessive diffusion into the tunnel oxide layer while maintaining sufficiently low contact resistivity through the cumulative effect of multiple doped regions.
Solution Approach 2:
Undoped or lightly doped polysilicon layers serve as intermediary barriers between the heavily doped polysilicon layers and the tunnel oxide layer. These intermediary layers physically block dopant diffusion pathways, protecting the tunnel oxide from degradation while allowing the doped layers to provide low contact resistivity.
3Reliability
If process parameters are optimized for tunnel oxide layer, then passivation quality improves, but polysilicon layer growth uniformity deteriorates
Solution Approach 1:
The polysilicon deposition process is segmented into multiple sequential steps, each forming a thin sub-layer. This allows process parameters to be optimized for each thin layer formation, ensuring uniform growth and consistent quality for each sub-layer, while the cumulative structure provides the required passivation performance.
Solution Approach 2:
The deposition process follows a periodic pattern of forming doped and undoped/lightly doped polysilicon sub-layers alternately. This periodic structure enables repeated optimization cycles where process parameters can be fine-tuned for each layer type, ensuring both passivation quality and growth uniformity are achieved through iterative process control.
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 method improves the passivation effect of the tunnel layer, increases open circuit voltage, and enhances the conversion efficiency of solar cells by balancing the process effects on the tunnel layer and doped stack structure.
Implementation Method 1
activating the dopant in the doped layer, such that the dopant diffuses into the polysilicon layers
Data Source
AI summary
The present application relates to a passivating contact structure and a preparation method thereof, and a solar cell and a preparation method thereof. In the method for preparing the passivating contact structure, a tunnel layer is formed on a side of a substrate; an initial stack structure is formed on a side of the tunnel layer away from the substrate. The initial stack structure includes polysilicon layers and a doped layer alternately stacked. In the initial stack structure, an innermost layer is most adjacent to the tunnel layer, an outermost layer is most away from the tunnel layer, the innermost layer and the outermost layer are both polysilicon layers. The doped layer is a polysilicon material layer doped with a dopant. The dopant is activated, such that the dopant diffuses into the polysilicon layers, thereby transforming the initial stack structure into a doped stack structure with uniform distribution of dopant.