Gallium-Doped P-Type Solar Cell Layout for Low Resistance Loss
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Solution Overview
Problem
Solar cells with PERC or PERL structures using boron-doped substrates experience light-induced degradation due to interstitial boron and oxygen combinations, leading to reduced minority carrier lifetime and resistance losses, while substituting with gallium-doped substrates does not sufficiently prevent resistance loss.
Innovation Solution
A solar cell with a gallium-doped P-type silicon substrate having a resistivity of 2.5 Ω·cm or less, where the back surface electrode pitch and substrate resistivity satisfy the relation log(Rsub)≤−log(Prm)+1.0, minimizing resistance loss and recombination rates, and maintaining high conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a boron-doped substrate is used to reduce manufacturing cost and achieve adequate electrical properties, then the substrate can be produced at relatively low cost via CZ method, but interstitial boron atoms combine with interstitial oxygen atoms under light irradiation to form recombination sites that reduce minority carrier lifetime and cause light-induced degradation
Solution Approach 1:
The patent changes the dopant type from boron to gallium in the P-type silicon substrate. This parameter change eliminates the light-induced degradation mechanism specific to boron-doped substrates while maintaining the electrical properties needed for solar cell operation. The gallium-doped substrate has resistivity of 2.5 Ω·cm or less and prevents the formation of recombination sites under light irradiation.
2Loss of energy
If the substrate resistivity is reduced to minimize resistance loss in PERC/PERL structures, then current crowding and resistance loss are reduced, but more boron atoms are contained which increases the combination with oxygen atoms and makes light-induced degradation more noticeable
Solution Approach 1:
The patent changes the dopant element from boron to gallium, allowing the substrate to achieve low resistivity (2.5 Ω·cm or less) without the harmful light-induced degradation effect. This parameter change decouples the trade-off between resistance loss and light-induced degradation, enabling both low resistance and high stability.
3Reliability
If gallium-doped substrate is used to eliminate light-induced degradation, then minority carrier lifetime is improved, but resistance loss is not sufficiently prevented
Solution Approach 1:
The patent optimizes the resistivity parameter of the gallium-doped substrate to be 2.5 Ω·cm or less. This parameter optimization ensures that the substrate provides both high reliability (by eliminating light-induced degradation) and low resistance loss, resolving the contradiction between these two requirements.
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 solution effectively eliminates light-induced degradation and resistance loss, enhancing the conversion efficiency of solar cells by using a gallium-doped substrate with a lower resistance, which reduces current crowding and recombination rates, thereby increasing output power.
Implementation Method 1
Semiconductor substrates for solar cells are usually manufactured by a Czochralski method (CZ method), which can produce a single crystal with a large-diameter at relatively low cost
Implementation Method 2
Single crystal silicon solar cells (solar cells made of single crystal silicon substrates) have been configured to have a structure in which the whole surface of the backside (the surface opposite to the light-receiving surface) is in contact with the electrode via a Back Surface Field (BSF) structure
Implementation Method 3
The solar cell is also provided with the passivation layer 116 on the back surface
Implementation Method 4
The PERC structure and the PERL structure are methods to aggressively reduce the recombination rate of minority carriers on the back surface, that is, methods to reduce an effective surface recombination velocity on the back surface
Data Source
AI summary
A method for manufacturing a solar cell having a P-type silicon substrate wherein one main surface is a light-receiving surface and another is a backside, a plurality of back surface electrodes formed on a part of the backside, an N-type layer in at least a part of the light-receiving surface, and contact areas in which the substrate contacts the electrodes; wherein the P-type silicon substrate is a silicon substrate doped with gallium and has a resistivity of 2.5 Ω·cm or less; and a back surface electrode pitch Prm [mm] of contact areas in which the P-type silicon substrate is in contact with the back surface electrodes and the resistivity Rsub [Ω·cm] of the substrate satisfy the relation represented by the following formula (1).log(Rsub)≤−log(Prm)+1.0 (1)