Graded-Density Silicon Solar Cell Passivation
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Solution Overview
Problem
High reflectivity of flat silicon surfaces in solar cells leads to significant light loss, and existing methods to reduce reflection, such as etching processes creating black silicon, result in large surface areas that decrease energy conversion efficiency unless high manufacturing costs are incurred.
Innovation Solution
A method integrating surface passivation with the diffusion or doping step of silicon wafers, using gaseous oxygen or water vapor to grow a silicon oxide layer on graded-density anti-reflective surfaces, eliminating the need for additional high-temperature passivation steps and dopant stripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If etching processes are used to create black silicon surfaces to reduce reflectivity, then optical losses are minimized, but surface area increases leading to loss of photogenerated minority carriers
Solution Approach 1:
The patent applies parameter changes by modifying the physical and chemical properties of the silicon surface through controlled oxidation. The black silicon surface is treated with oxygen plasma or chemical oxidants to transform the surface morphology and create a porous oxidized layer with reduced surface area, thereby maintaining anti-reflective properties while reducing carrier recombination losses.
Solution Approach 2:
The patent creates a composite structure by combining black silicon with oxidized silicon layers. The resulting structure has both the anti-reflective properties of black silicon and the passivation benefits of the oxidized layer, forming a multi-functional surface that addresses both optical and electrical performance requirements.
2Manufacturing precision
If dopant-containing precursors are used during high-temperature processing, then emitter junction formation is achieved, but additional manufacturing steps for stripping dopants are required
Solution Approach 1:
The patent merges the dopant removal step with the existing high-temperature processing step used for emitter junction formation. The same thermal treatment that forms the emitter junction also serves to drive off and remove the dopant-containing precursor, eliminating the need for a separate stripping step and simplifying the manufacturing process.
Solution Approach 2:
The high-temperature processing step performs dual functions: it forms the emitter junction and simultaneously removes the dopant precursor through thermal decomposition or evaporation. The process is self-sufficient, using its own thermal energy to achieve both objectives without requiring additional dedicated steps.
3Reliability
If separate high-temperature passivation steps are implemented, then surface passivation is achieved, but manufacturing complexity and fabrication time increase
Solution Approach 1:
The patent combines surface passivation with the high-temperature processing step used for emitter junction formation. The same thermal treatment that forms the emitter junction also provides surface passivation by oxidizing the silicon surface and removing dangling bonds, thereby achieving dual benefits in a single step and reducing overall fabrication time.
Solution Approach 2:
The high-temperature processing step is designed to perform multiple functions simultaneously: emitter junction formation, surface passivation, and dopant precursor removal. This multi-functional approach eliminates the need for separate dedicated steps for each function, streamlining the manufacturing process and improving productivity.
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 energy conversion efficiency of silicon solar cells from 14% to over 16% by effectively reducing reflectivity and maintaining the anti-reflective properties without increasing manufacturing complexity or costs.
Implementation Method 1
using gaseous oxygen or water vapor to grow a silicon oxide layer on graded-density anti-reflective surfaces
Implementation Method 2
integrates passivation with the diffusion or doping step used to process the silicon wafer or substrate to provide an emitter junction
Data Source
AI summary
A method (50) is provided for processing a graded-density AR silicon surface (14) to provide effective surface passivation. The method (50) includes positioning a substrate or wafer (12) with a silicon surface (14) in a reaction or processing chamber (42). The silicon surface (14) has been processed (52) to be an AR surface with a density gradient or region of black silicon. The method (50) continues with heating (54) the chamber (42) to a high temperature for both doping and surface passivation. The method (50) includes forming (58), with a dopant-containing precursor in contact with the silicon surface (14) of the substrate (12), an emitter junction (16) proximate to the silicon surface (14) by doping the substrate (12). The method (50) further includes, while the chamber is maintained at the high or raised temperature, forming (62) a passivation layer (19) on the graded-density silicon anti-reflection surface (14).