Gallium-Doped PolySi/SiO2 Passivated Contacts
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Solution Overview
Problem
P-type polySi/SiO2 passivated contacts in solar cells have lower open circuit voltage (iVoc) and saturation current density (Joe) values due to low diffusivity of boron in SiO2, leading to pileup of boron at the SiO2 tunneling layer and increased hydrogen concentrations, which impede effective passivation.
Innovation Solution
Using gallium as a p-type dopant in polySi/SiO2 contacts, incorporating gallium through ion implantation or spin-on dopants, and annealing at specific temperatures to achieve uniformly doped layers and reduce dopant-related defects, resulting in improved passivation characteristics and contact resistivities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If boron is used as dopant in polySi/SiO2 contacts, then p-type doping is achieved, but low diffusivity of B in SiO2 causes pileup at SiO2 tunneling layer and increased H concentrations, resulting in lower iVoc values around 700 mV
Solution Approach 1:
The patent changes the dopant parameter from boron to gallium. Gallium has higher diffusivity in SiO2 compared to boron, which prevents dopant pileup at the SiO2 tunneling layer. This parameter change resolves the contradiction by eliminating the harmful pileup effect while maintaining p-type doping functionality, achieving improved passivation quality with iVoc values of 720-732 mV.
2Reliability
If boron doping is used in polySi/SiO2 contacts, then p-type conductivity is achieved, but low diffusivity leads to increased H concentrations and dopant-related defects, reducing Joe values
Solution Approach 1:
The patent substitutes gallium for boron as the dopant material. Gallium's superior diffusivity in SiO2 ensures uniform distribution of dopant atoms throughout the contact structure, preventing localized concentration buildup. This resolves the contradiction by achieving both adequate p-type conductivity and uniform dopant distribution, resulting in lower Joe values of 8.2-3.1 fA/cm2.
3Ease of manufacture
If gallium is used as dopant instead of boron, then diffusivity in SiO2 is improved, but new dopant-related defects may be introduced
Solution Approach 1:
The patent converts the potential harm of introducing a new dopant (gallium) into a benefit by selecting gallium specifically for its favorable diffusivity properties in SiO2. The higher diffusivity prevents pileup and promotes uniform distribution, which outweighs potential defect concerns. The annealing process parameters are optimized to activate gallium effectively while minimizing defect formation, transforming the challenge of dopant selection into an advantage for passivation quality.
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 gallium-doped polySi/SiO2 contacts exhibit iVoc values of 720-732 mV and Joe values of 8.2-3.1 fA/cm2, with reduced dopant pileup and defects, enhancing the passivation quality and efficiency of solar cells.
Implementation Method 1
providing a silicon substrate wherein the substrate is doped using ion implantation of gallium
Implementation Method 2
the doped substrate is annealed and passivated
Data Source
AI summary
PolySi:Ga/SiO2 passivated contacts were prepared using ion implantation and dopant inks to introduce Ga into a-Si. Following crystallization anneals these p-type contacts exhibited improved passivation (iVoc of about 730 mV) over B-doped passivated contacts for solar cells.