CIGS Solar Cell Buffer Layer via pH-Controlled CBD
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Solution Overview
Problem
Conventional compound semiconductor thin-film solar cells face defects in the junction between the p-type light absorbing layer and n-type buffer layer due to chemical composition differences, leading to variations in power conversion efficiency and difficulty in passing short wavelengths of light.
Innovation Solution
A method using the Chemical Bath Deposition (CBD) process to form an n-type buffer layer with stepwise increasing particle sizes and pH-regulated InS deposits, ensuring improved crystallinity and adherence to the light absorbing layer, enhancing optical transmittance and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer layer of InS is formed by CBD method to achieve uniform composition and reproducibility, then the heterojunction suitability to CIGS light absorbing layer is improved, but the small band gap of InS makes it hard to pass light of short wavelengths, resulting in low Jsc
Solution Approach 1:
The patent changes the chemical composition parameters of the buffer layer by replacing InS with ZnO or In2O3 materials, which have larger band gaps and better optical transmittance properties while maintaining the heterojunction functionality with CIGS light absorbing layer
Solution Approach 2:
The patent uses composite material structures where the buffer layer is formed as a multi-layer system with different functional layers (e.g., ZnO layer, In2O3 layer, and transition layers) to combine the advantages of different materials for both electrical heterojunction formation and optical transmittance
2Ease of manufacture
If Zn element diffuses into the light absorbing layer and ZnS film forms during dipping, then the heterojunction is formed, but variations in power conversion efficiency occur due to differences in crystallinity and surface conditions
Solution Approach 1:
The patent replaces the conventional CBD wet chemical deposition method with a sputtering physical vapor deposition method to form the buffer layer, which provides better control over film thickness, composition, and crystallinity, thereby reducing variations in power conversion efficiency
Solution Approach 2:
The patent changes the deposition method parameters from chemical solution-based CBD to physical sputtering with controlled gas pressure, power, and substrate temperature, enabling precise control over the buffer layer properties and reducing manufacturing variations
3Device complexity
If a heterojunction buffer layer is formed between p-type light absorbing layer and n-type semiconductor layer, then the solar cell structure is completed, but defects easily occur in the junction due to large differences in chemical compositions
Solution Approach 1:
The patent introduces intermediate transition layers (such as ZnO or In2O3 layers) between the p-type CIGS light absorbing layer and the n-type buffer layer to serve as mediators that gradually transition the chemical composition and crystal structure, reducing the abrupt interface discontinuity and minimizing defect formation
Solution Approach 2:
The patent uses buffer layer materials (ZnO, In2O3) that have crystal structures and chemical compositions more similar to CIGS than conventional InS, creating a more homogeneous interface that reduces lattice mismatch and minimizes defect formation at the heterojunction
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 achieves high optical transmittance, tight adherence to the light absorbing layer, and conformity with the transparent electrode, overcoming the limitations of small bandgap InS material by regulating particle sizes and pH, resulting in improved power conversion efficiency and durability.
Implementation Method 1
the buffer layer is formed by applying a chemical bath deposition (CBD) process using an aqueous solution for dipping the light absorbing layer
Implementation Method 2
The CBD process according to the present invention specifically increases sizes of particles to be deposited by conducting a first step of maintaining the solution at a first temperature for a first preset time, a second step of increasing the temperature of the solution from the first temperature to a second higher temperature for a second preset time and a third step of maintaining the solution at the second temperature for a third preset time
Implementation Method 3
a compound semiconductor thin-film solar cell having an n-type buffer layer for heterojunction with a light absorbing layer
Data Source
AI summary
A method of fabricating a thin-film compound solar cell having an n-type buffer layer formed therein for providing a heterojunction with a p-type compound semiconductor light absorbing layer formed on a back electrode by applying a chemical bath deposition (CBD) process using an aqueous solution for dipping the light absorbing layer to deposit particles on the surface thereof. In this process, the temperature of the solution is controlled from low to high to increase sizes of the particles to be deposited on the light absorbing layer so as to form the buffer layer which possesses a high optical transmittance, tight adherence to the light absorbing layer and conformity with the transparent electrode formed thereon even if it would be made of InS material generally possessing a small bandgap and hard to pass light of short wavelengths.