Polycrystalline Silicon Solar Cell Vertical Grain Structure
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Solution Overview
Problem
Current solar cell technologies face challenges in achieving high efficiency due to metal contamination and random grain growth in polycrystalline silicon thin films, leading to increased recombination sites for electrons and holes, which decreases solar cell efficiency and stability.
Innovation Solution
A method involving metal-induced lateral crystallization (MILC) and metal-induced vertical crystallization (MIVC) processes is used to form a light-absorbing layer with a vertical columnar structure, minimizing grain boundaries by using polycrystalline silicon as a seed for crystallization, and removing metal and silicide impurities to prevent contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metal-induced crystallization (MIC) is used to form polycrystalline silicon thin film, then crystallization can be achieved at low temperature, but metal contamination occurs which increases recombination sites and decreases solar cell efficiency
Solution Approach 1:
The patent extracts and removes metal catalysts and silicide impurities from the polycrystalline silicon thin film after crystallization. This is achieved through selective etching processes that remove the metal contaminants while preserving the silicon structure, thereby eliminating the harmful metal contamination that causes recombination sites without sacrificing the low-temperature crystallization benefit
Solution Approach 2:
The patent uses an intermediary substance (etchant or chemical agent) to selectively remove metal catalysts and silicide impurities from the crystallized silicon film. This intermediary enables the separation of the crystallization function (performed by metal at low temperature) from the contamination problem (metal remaining in the film), allowing both low-temperature processing and high purity to be achieved
2Object-generated harmful factors
If conventional crystallization methods are used to form polycrystalline silicon, then metal contamination is avoided, but high temperature processing is required which increases production cost and reduces productivity
Solution Approach 1:
The patent performs preliminary crystallization at low temperature using metal-induced crystallization to form the polycrystalline silicon structure, then subsequently removes the metal contaminants. This preliminary action allows the crystallization process to occur at lower temperatures with faster kinetics, improving productivity, while the metal removal step eliminates contamination concerns
3Ease of manufacture
If random grain growth occurs in polycrystalline silicon, then crystallization is simple to achieve, but numerous grain boundaries are formed which act as recombination sites and decrease solar cell efficiency
Solution Approach 1:
The patent applies local quality control by creating specific local conditions during crystallization that promote vertical columnar grain growth rather than random grain growth. This is achieved through controlled deposition conditions and substrate temperature gradients that favor epitaxial-like vertical growth, reducing grain boundaries in the light-absorbing direction while maintaining manufacturing feasibility
Solution Approach 2:
The patent transitions from two-dimensional random grain growth to three-dimensional vertical columnar grain growth. By controlling the crystallization process to grow grains vertically perpendicular to the substrate, the patent reduces the number of grain boundaries that electrons and holes must cross, thereby reducing recombination sites while maintaining a relatively simple crystallization process
4Loss of substance
If silicon wafer thickness is reduced to 300 μm or less, then material usage is improved, but the wafer becomes difficult to cut and prone to damage in subsequent processes
Solution Approach 1:
The patent replaces the mechanical cutting process with a thin-film deposition and crystallization process. Instead of cutting thick wafers to reduce material usage, the patent deposits silicon as a thin film and crystallizes it in-situ, achieving the desired thickness without mechanical cutting. This eliminates the risk of wafer damage while optimizing material usage
Solution Approach 2:
The patent uses thin-film silicon structures that can be deposited at controlled thicknesses (300 μm or less) without the mechanical constraints of wafer cutting. The thin-film approach allows for precise thickness control and eliminates the fragility issues associated with thin wafers, as the film is formed and strengthened in-situ through the crystallization process
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 solar cell efficiency by reducing recombination sites and maintaining high productivity while using low temperatures, thus improving the overall performance and cost-effectiveness of polycrystalline silicon solar cells.
Implementation Method 1
vertically crystallizing an intrinsic amorphous silicon layer using the polycrystalline silicon layer as a seed for crystallization through a metal induced vertical crystallization (MIVC) process
Implementation Method 2
formed by vertically crystallizing an intrinsic amorphous silicon layer using the polycrystalline silicon layer as a seed for crystallization through a metal induced vertical crystallization (MIVC) process
Implementation Method 3
Solar photovoltaic power generation, which is a technology of directly converting solar energy into electric energy using a photovoltaic effect
Data Source
AI summary
Disclosed herein is a polycrystalline silicon solar cell, including: a back electrode formed on a transparent insulating substrate; an N-type polycrystalline silicon layer in which amorphous silicon is crystallized through MIC process, and in which electrons are accumulated; a light-absorbing layer which is formed by vertically crystallizing an intrinsic amorphous silicon layer using the polycrystalline silicon layer as a seed for crystallization through MIVC process, in which pairs of electrons and holes are generated in response to incident light, and which has a vertical column grain structure in which grains are arranged in the direction in which electrons and holes move; a P-type polycrystalline silicon layer which has the vertical column grain structure, and in which holes are accumulated; a transparent electrode layer; front electrodes; and an antireflection coating film, and is a method of fabricating the same.