Multilayer Back Contact for Flexible CIGS Photovoltaics
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Solution Overview
Problem
Flexible photovoltaic modules, particularly those with Copper-Indium-Gallium-Selenide (CIGS) devices, face challenges in maintaining mechanical integrity due to intrinsic and extrinsic stresses during thin-film deposition on polymer substrates, leading to distortion and performance issues.
Innovation Solution
A multilayer back contact structure is used, comprising a dielectric film on the polymer substrate's back side and a high-conductivity metallic film layer with a thin molybdenum cap, which balances stresses and maintains electrical conductivity, reducing sheet resistance and interconnect losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic back contact is deposited onto the polymer substrate prior to CIGS deposition, then electrical conductivity is improved, but mechanical distortion and stress increase during processing
Solution Approach 1:
The back contact is segmented into multiple functional layers: a stress-balancing dielectric layer on the polymer substrate, and a conductive metal layer (such as molybdenum or aluminum) deposited on the device side. This segmentation allows the dielectric layer to absorb thermal expansion stresses while the metal layer maintains electrical conductivity, resolving the contradiction between conductivity and mechanical stability.
Solution Approach 2:
The back contact system uses composite material structure combining dielectric material (for stress management) and conductive metal material (for electrical conductivity). The dielectric layer has different thermal expansion properties than the metal layer, creating a composite structure that balances stresses during temperature variations while maintaining overall electrical conductivity for current collection.
2Reliability
If high-conductivity metal layers are used to reduce sheet resistance, then electrical performance is improved, but material cost and deposition complexity increase
Solution Approach 1:
The invention optimizes deposition parameters such as pressure (less than 20 millitorr for sputtering), layer thickness, and material composition to achieve high conductivity with simpler processes. By controlling these parameters, the patent reduces sheet resistance effectively without requiring excessively complex multi-step deposition sequences or rare materials.
Solution Approach 2:
The patent employs cost-effective metal materials such as aluminum or thin molybdenum layers instead of expensive alternatives. The thin-film metal layer is designed to be sufficiently conductive for its intended function while minimizing material usage and cost, achieving economical performance without sacrificing electrical reliability.
3Quantity of substance
If the metal layer is made thinner to reduce material usage, then cost is reduced, but electrical conductivity and current collection efficiency decrease
Solution Approach 1:
The invention carefully optimizes the thickness parameter of the metal layer to achieve the minimum required thickness that still provides adequate electrical conductivity. By precisely controlling thickness within specific ranges, the patent minimizes metal material usage while maintaining sufficient current collection efficiency for practical photovoltaic operation.
Solution Approach 2:
The composite structure of dielectric layer plus thin metal layer creates synergistic effects where the dielectric provides mechanical stability and stress balancing, allowing the metal layer to be thinner while still achieving required electrical performance. The combination compensates for the reduced metal thickness through the supportive dielectric framework.
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 significantly reduces stress-related distortions, enhances electrical conductivity, and increases cell pitch, resulting in improved power output and reduced module losses, while also minimizing the use of expensive molybdenum and simplifying the deposition process.
Implementation Method 1
A layer of dielectric is formed at the back side of the polymer substrate... balances stresses and maintains electrical conductivity, reducing sheet resistance and interconnect losses
Implementation Method 2
This back contact makes ohmic contact to the CIGS and allows for current to flow through the device and be collected through interconnects to the leads
Implementation Method 3
disposing a molybdenum cap layer on the metallic film layer at least partially using a vacuum-based sputter deposition process at a pressure of less than 20 millitorr
Data Source
AI summary
A polymer substrate and back contact structure for a photovoltaic element, and a photovoltaic element include a CIGS photovoltaic structure, a polymer substrate having a device side at which the photovoltaic element can be located and a back side opposite the device side. A layer of dielectric is optionally formed at the back side of the polymer substrate. A metal structure is formed at the device side of the polymer substrate.