Homogeneous Linear Evaporation Source for CIGS Roll-to-Roll Deposition
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Solution Overview
Problem
The challenge in roll-to-roll deposition processes for CIGS solar cells is achieving uniform evaporation of source materials across large substrates, as the evaporation rate is difficult to control due to thermal disturbances and varying fill levels in crucibles, leading to non-uniform deposition.
Innovation Solution
The evaporation source design includes a crucible with a heating system that provides differential heat distribution, with the first outer region receiving more heat than the central region, and a lid assembly with varying opening sizes and spacings to control the effusion of vapor, ensuring consistent deposition across the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional crucible with uniform heating is used, then the evaporation source is simple in structure, but the deposition uniformity across the substrate deteriorates due to heat losses at outer regions
Solution Approach 1:
The heating system is designed with multiple heating zones (first outer region, second outer region, and central region) that can be independently controlled to provide different heat rates to different spatial locations. This local quality approach compensates for heat losses at outer regions by providing higher heat rates there compared to the central region, thereby achieving uniform evaporation and deposition across the substrate.
Solution Approach 2:
The heating system is segmented into distinct heating zones with independent control. The lid assembly is also segmented with multiple sets of openings (first plurality, second plurality, third plurality) at different locations, allowing independent control of vapor effusion from different regions. This segmentation enables precise control over the evaporation profile to achieve uniform deposition.
2Productivity
If the evaporation rate is increased to improve productivity, then more material is deposited per unit time, but the evaporation rate becomes harder to control uniformly across the substrate
Solution Approach 1:
The heating system and lid assembly are designed to dynamically adjust heat distribution and vapor effusion independently for different regions. The controller can modify the heat rate to each heating zone and the opening configuration in real-time based on feedback or predetermined profiles, allowing the system to maintain uniform evaporation rates even at high productivity levels.
Solution Approach 2:
The system changes physical parameters (heat rate, opening size, opening spacing) in different spatial regions to control the evaporation rate. By varying these parameters across the crucible interior region, the system achieves uniform material effusion from different locations, maintaining deposition uniformity while operating at high productivity.
3Manufacturing precision
If a lid with uniform openings is used, then the lid structure is simple, but thermal disturbances from other evaporation sources affect the deposition uniformity
Solution Approach 1:
The lid assembly is designed with different opening characteristics for different regions: the first outer section has a first plurality of openings, the second outer section has a second plurality of openings, and the inner section has a third plurality of openings. The openings in the third plurality are spaced farther apart than the openings in the first plurality, creating local variations in vapor effusion that compensate for thermal disturbances and achieve uniform deposition.
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 design enhances the uniformity of material deposition on large substrates by compensating for heat losses and maintaining a consistent evaporation rate, improving the quality of CIGS solar cells by ensuring uniform coating.
Implementation Method 1
a first heater disposed in the base, the first heater configured to provide heat at a higher rate to the first outer region than to the central region
Implementation Method 2
a lid disposed over the interior region, the lid including a first outer section including a first plurality of openings, a second outer section including a second plurality of openings, and an inner section including a third plurality of openings
Implementation Method 3
an evaporation source for depositing a source material on a substrate
Data Source
AI summary
Embodiments of the present disclosure generally relate to evaporation sources used for physical vapor deposition of material onto substrates and more particularly for controlled coating of large substrates, such as vacuum deposition of copper, indium, gallium, selenium, tellurium, cadmium, or zinc on flexible substrates. Embodiments disclosed herein are able to control the evaporation rate of the source material during processing so as to obtain a uniform deposition across the width of the substrate as the complete length of a roll-to-roll substrate is moved past the evaporation source during processing.