Multi-Stage Paste Coating for Dense CIGS Solar Cell Films
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Solution Overview
Problem
Conventional methods for producing chalcopyrite compound thin films for solar cells using solution processes result in low efficiency due to porous film structures and uneven element distribution, leading to shunt paths and electron-hole recombination, which deteriorate solar cell performance and increase production costs.
Innovation Solution
A multi-stage paste or ink coating method is employed, where different metal precursors and organic binders are mixed with water-soluble solvents to form pastes with varying viscosities, which are coated and thermally treated in specific atmospheres to produce dense chalcopyrite compound thin films with controlled Ga concentration distributions, eliminating the need for vacuum systems and minimizing raw material consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vacuum deposition methods (co-evaporation or sputtering) are used to produce CIS or CIGS thin films, then the film quality and photoelectric conversion efficiency are improved, but the fabrication cost increases due to expensive vacuum systems and loss of costly raw materials
Solution Approach 1:
The patent replaces the mechanical vacuum deposition system with a chemical solution-based printing system. Instead of using vacuum chambers and sputtering equipment to deposit metal targets, the invention uses solution processes where metal precursors are dissolved in solvents, mixed with organic binders to form pastes, and printed onto substrates using simple printing equipment, thereby eliminating expensive vacuum systems while achieving comparable film quality
Solution Approach 2:
The patent changes the physical and chemical parameters of the deposition process by transitioning from vapor-phase deposition to solution-phase deposition. The metal precursors are transformed from solid metal targets to dissolved ionic forms in solution, and the deposition mechanism changes from physical sputtering to chemical decomposition and reduction during thermal treatment, enabling cost-effective large-area fabrication
2Productivity
If single-stage paste coating is used to produce CIGS thin films, then the processing speed and large-area production capability are improved, but the film density and element distribution uniformity deteriorate due to porous structures
Solution Approach 1:
The patent divides the single-stage coating process into multiple sequential coating stages. Different metal precursor pastes are applied in separate stages, allowing each layer to be optimized for specific element distribution. This multi-stage approach enables better control over film density and compositional uniformity while maintaining the benefits of solution-based printing for large-area production
Solution Approach 2:
The patent applies different paste compositions and coating parameters to different regions or stages of the film formation process. By controlling the local properties of each coating stage (such as paste viscosity, drying conditions, and thermal treatment parameters), the invention achieves uniform element distribution and dense film structure across the entire large-area substrate
3Device complexity
If conventional solution processes are used to produce CIGS thin films, then the fabrication cost is reduced by eliminating vacuum systems, but the solar cell efficiency deteriorates due to porous film structures causing shunt paths and electron-hole recombination
Solution Approach 1:
The patent performs preliminary actions during the paste preparation and coating stages to prevent porous structure formation. The paste formulations are specifically designed with appropriate viscosity and composition to ensure dense film formation upon drying. Thermal treatment parameters are pre-optimized to promote complete decomposition of organic binders and formation of dense inorganic film structures, preventing pore formation before it can affect device performance
Solution Approach 2:
The patent uses composite paste formulations combining metal precursors with organic binders and additives. These composite materials are designed to decompose during thermal treatment, leaving behind dense inorganic chalcopyrite films. The organic components serve as temporary scaffolds that are completely removed during processing, replacing the porous structure with dense crystalline film while maintaining the low-cost solution processing advantage
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 method enables the production of high-quality, dense chalcopyrite compound thin films with improved compaction and element distribution, enhancing solar cell efficiency and reducing production costs by allowing large-area, high-speed fabrication without vacuum systems.
Implementation Method 1
thermally treating the coated conductive substrate in air or an oxygen atmosphere to obtain a mixed oxide thin film
Implementation Method 2
thermally treating the mixed oxide thin film in a sulfur gas, a selenium gas or a sulfur/selenium mixed gas atmosphere to form a sulfide or selenide thin film
Data Source
AI summary
Disclosed are methods for producing chalcopyrite compound (e.g., copper indium selenide (CIS), copper indium gallium selenide (CIGS), copper indium sulfide (CIS) or copper indium gallium sulfide (CIGS)) thin films. The methods are based on solution processes, such as printing, particularly, multi-stage coating of pastes or inks of precursors having different physical properties. Chalcopyrite compound thin films produced by the methods can be used as light-absorbing layers for thin-film solar cells. The use of the chalcopyrite compound thin films enables the fabrication of thin-film solar cells with improved efficiency at low costs.