Ink Printing Thin Solar Cells Using Segmented Particle Inks
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Solution Overview
Problem
Current methods for producing thin film solar cells using IB-IIIA-VIA semiconductor materials face challenges such as non-uniform composition, high production costs, and complex reduction/selenization processes, which hinder the efficiency and scalability of CuInGaSe (CIGS) solar cells.
Innovation Solution
A semiconductive ink composition comprising micro-sized and nano-sized IB-IIIA-VIA particles, an ink stabilizer solvent, and a liquid vehicle is developed for direct printing of CIGS thin films, allowing for the formation of large crystal grain size films with improved uniformity and efficiency, using a combination of micron-sized particles as 'bricks' and nano-sized particles as 'binders' to stabilize and bind the film, along with optional chalcogen elements to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical vapor evaporation (PVE) process is used to achieve high solar cell efficiency, then energy conversion efficiency is improved (up to 19.9%), but manufacturing complexity and production cost increase due to point-evaporation nature and difficulty in uniform composition control
Solution Approach 1:
The patent replaces the mechanical physical vapor evaporation process with a chemical solution-based printing process. Instead of using complex PVE equipment to deposit materials atom by atom, the invention uses inkjet or screen printing to deposit precursor solutions containing metal salts, which are then converted to functional films through low-temperature annealing. This substitution dramatically simplifies the manufacturing equipment while maintaining film quality.
Solution Approach 2:
The patent changes the deposition parameters from high-vacuum, high-energy physical vapor deposition to low-temperature, solution-based chemical deposition. The processing temperature is reduced from hundreds of degrees (PVE) to below 100°C (annealing of printed films), and the deposition mechanism changes from physical vapor condensation to chemical precursor transformation, enabling simpler and more scalable manufacturing.
2Ease of manufacture
If screen printing technique with milled fine powder is used to form preliminary film, then deposition process is simplified, but composition uniformity deteriorates due to large metal particle size (up to 2 μm) and high sintering temperature causing indium loss
Solution Approach 1:
The patent segments the metal particles into two distinct size ranges: nano-sized particles (1-100 nm) for uniform distribution and composition control, and micro-sized particles (1-10 μm) for forming the film matrix and large crystal grains. This segmentation allows each particle size to fulfill its specific function, achieving both ease of deposition and composition uniformity that neither size alone could provide.
Solution Approach 2:
The patent creates a composite ink formulation containing both nano-sized and micro-sized metal particles suspended in a liquid vehicle. This composite structure combines the advantages of fine particles (uniform distribution, low sintering temperature) with coarse particles (film formation, crystal growth), enabling simultaneous achievement of deposition simplicity and composition precision through a single printing step.
3Manufacturing precision
If nanoparticles are used to achieve fixed composition ratios, then composition control is improved, but crystal grain size deteriorates as particles remain largely amorphous and form undesired films for high performance photovoltaic cells
Solution Approach 1:
The patent merges nano-sized particles (providing composition precision and uniformity) with micro-sized particles (providing crystal grain growth centers) in a single ink formulation. The nano-particles ensure fixed stoichiometric ratios and uniform distribution, while the micro-particles serve as nucleation sites that grow into large crystal grains during low-temperature annealing, achieving both precise composition control and large crystal grain formation.
Solution Approach 2:
The patent assigns different functional qualities to different particle sizes within the same ink: nano-sized particles provide local compositional precision and uniformity, while micro-sized particles provide local crystal growth centers for large grain formation. This local differentiation of particle functions within the composite ink enables simultaneous achievement of composition control and crystal grain development.
4Manufacturing precision
If oxide-based methods are used to make IB-IIIA-VIA semiconductor compounds, then composition ratio control is improved, but process complexity increases due to extra reduction and selenization steps required
Solution Approach 1:
The patent extracts and eliminates the complex reduction and selenization steps required by oxide-based methods. Instead of using metal oxides that require high-temperature reduction and subsequent selenization, the invention directly uses metal salts (nitrates, acetates, chlorides) as precursors that can be converted to functional semiconductor films through simple low-temperature annealing in inert or reducing atmosphere, removing unnecessary process complexity while maintaining composition precision.
Solution Approach 2:
The patent changes the precursor chemistry from stable metal oxides requiring high-temperature reduction to reactive metal salts that can be directly converted to functional films at lower temperatures. This parameter change in precursor selection eliminates the need for multi-step reduction and selenization processes, simplifying the overall manufacturing process while maintaining precise composition control through solution-based 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
The ink formulation enables the production of high-performance solar cells with improved energy conversion efficiency and reduced production costs by facilitating the formation of dense, polycrystalline films with large crystal grains, overcoming the limitations of previous methods.
Implementation Method 1
The ink stabilizer solvent is a liquid solvent containing heteroatom N, O, P, S with a boiling point between 50-300° C. The lone pair electrons on the heteroatom play the role to co-ordinate with particles of CIGS and thus stabilize the particles in the ink and prevent coagulation of particles
Implementation Method 2
A non-aqueous liquid vehicle such as a mixture of butyl acetate and anisole in a volume ratio of 1:1 to 4:1
Implementation Method 3
Due to the non-uniformity of composition caused by the large metal particle size (up to 2 μm), and the high sintering temperature, which causes indium loss and deforms the soda-lime glass substrate
Data Source
AI summary
Semiconductor ink is disclosed for use in printing thin film solar cell absorber layer. The semiconductor ink is particularly useful in fabricating multi junction tandem solar cell wherein a high bandgap absorber layer as the top cell and a lower band gap absorber layer as the bottom cell. The ink contains ingredients of IB-IIIA-VIA compound with micron-sized semiconductor as the main building “bricks” and nano-sized semiconductor as the binder to fulfill the formation of smooth semiconductive film with micron-sized crystal grain size. Thus formed ink can be used in direct printing for the fabrication of low cost high performance solar cells.