Solar Cell Rear-Surface Passivation Using Sub-Saturated ALD
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Solution Overview
Problem
Silicon solar cells face efficiency losses due to recombination of minority charge carriers at the rear surface, which is not adequately addressed by existing passivation methods, leading to suboptimal effective minority charge carrier lifetime.
Innovation Solution
A method involving sub-saturated Atomic Layer Deposition (ALD) of a metal oxide layer, specifically aluminum oxide, using trimethylaluminum and ozone precursors, with controlled process parameters such as ALD cycle time, ozone concentration, and layer thickness to achieve enhanced passivation without reaching saturation, thereby increasing effective minority charge carrier lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ALD deposition is performed to saturation to ensure complete surface coverage, then passivation quality is improved, but production time and cost increase
Solution Approach 1:
The patent applies partial action by stopping the ALD deposition process before saturation is reached. The precursor exposure time is deliberately limited to achieve sub-saturated coverage, which provides sufficient passivation quality while reducing deposition time and production costs. This partial action principle resolves the contradiction by demonstrating that complete saturation is not necessary to achieve the required passivation effect.
Solution Approach 2:
The patent changes the deposition parameters by controlling the precursor exposure time to achieve sub-saturated conditions. By adjusting this parameter, the process achieves optimal passivation quality at reduced deposition times, thereby resolving the contradiction between passivation quality and production time.
2Productivity
If ALD deposition is performed at high growth rates to increase productivity, then production time is reduced, but passivation quality deteriorates
Solution Approach 1:
The patent optimizes the precursor exposure time parameter to achieve sub-saturated deposition conditions. This parameter optimization enables the process to achieve good passivation quality at practical deposition rates, resolving the contradiction between productivity and passivation quality by finding the optimal balance point rather than operating at extremes.
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 method significantly boosts the effective minority charge carrier lifetime of solar cells to over 750 µs, improving efficiency and reducing production costs by optimizing passivation layer properties and precursor usage.
Implementation Method 1
passivating a surface of said wafer by ALD-depositing a metal oxide layer on said surface by sequentially and alternatingly (i) exposing said surface to a first precursor, resulting in a coverage of the surface with the first precursor, and (ii) exposing said surface to a second precursor, resulting in a coverage of the surface with the second precursor
Implementation Method 2
To reduce the occurrence of recombinations at the rear surface of a solar cell, this surface may be passivated by providing it with a metal oxide passivation layer, e.g. an aluminum oxide (Al 2 O 3) layer
Data Source
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AI summary
A method of manufacturing a solar cell having an effective minority charge carrier lifetime (τeff) of at least 500 µs, said method comprising: - providing a semiconductor wafer; and - passivating a surface of said wafer by ALD-depositing a metal oxide layer on said surface by sequentially and alternatingly: (v) exposing said surface to a first precursor, resulting in a coverage of the surface with the first precursor, and (vi) exposing said surface to a second precursor, resulting in a coverage of the surface with the second precursor, wherein at least one of steps (i) and (ii) is stopped before the coverage of the surface reaches a saturation level.