Solar Cell Cap Layer Doping Barrier for Voltage Loss
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Solution Overview
Problem
The integration of a bypass diode in multi-junction solar cells can reduce the open circuit voltage (Voc) of the top sub-cell, which is undesirable and degrades the cell's performance.
Innovation Solution
Incorporating an undoped or unintentionally doped barrier layer with significantly lower silicon density between the doped cap layer and the window layer to prevent silicon diffusion and maintain higher silicon concentration in the cap layer, thereby reducing recombination losses and increasing the open circuit voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an integrated bypass diode is fabricated in the solar cell structure, then reverse bias protection is improved, but the open circuit voltage of the top sub-cell deteriorates
Solution Approach 1:
An undoped or unintentionally doped barrier layer is introduced as an intermediary between the doped cap layer and the window layer. This barrier layer has significantly lower silicon density than the cap layer, preventing silicon diffusion into the window layer while allowing the integrated bypass diode to function for reverse bias protection.
Solution Approach 2:
The barrier layer is positioned specifically between the cap layer and window layer where silicon diffusion occurs. By creating a localized region with different doping characteristics (undoped or unintentionally doped versus doped cap layer), the patent prevents harmful silicon diffusion in the critical interface region while maintaining the overall structure's functionality.
2Power
If silicon concentration in the cap layer is increased to reduce recombination losses, then open circuit voltage is improved, but silicon diffusion into the window layer worsens
Solution Approach 1:
The barrier layer serves as a physical and chemical intermediary that blocks silicon diffusion from the high-concentration cap layer into the window layer. This allows the cap layer to maintain high silicon concentration for reduced recombination losses without causing contamination in the window layer.
Solution Approach 2:
The harmful silicon diffusion process is effectively extracted or removed from the system by introducing the barrier layer. The barrier layer captures and prevents silicon atoms from migrating into the window layer, allowing the cap layer to have high silicon concentration without the negative consequence of diffusion.
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 enhances the open circuit voltage and operating voltage of the solar cell, leading to improved efficiency and performance by minimizing silicon diffusion into the window layer.
Implementation Method 1
Incorporating an undoped or unintentionally doped barrier layer with significantly lower silicon density between the doped cap layer and the window layer to prevent silicon diffusion
Data Source
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AI summary
A solar cell includes a semiconductor substrate and a sequence of semiconductor layers disposed over the substrate including a window layer. The solar cell also includes a semiconductor silicon-containing cap layer over the window layer. The cap layer is spatially separated from the window layer by a semiconductor barrier layer that either includes no silicon or has a silicon concentration that is significantly lower than the silicon concentration of the cap layer.