Thin-Film Solar Cell Composition Gradient
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Solution Overview
Problem
Conventional CIS-based thin-film solar cells face challenges in achieving high photoelectric conversion efficiency due to defects and recombination centers in the p-type light absorption layer, particularly with Ga and Cu composition ratios affecting the p-type polarity and efficiency.
Innovation Solution
A thin-film solar cell structure is developed with a p-type light absorption layer composed of a Group I-III-VI 2 compound, where the atomic ratio of Cu to Group III elements is less than 1.0 overall but 1.0 or higher near the n-type second electrode layer, and the ratio of Ga to Group III elements is 0.13 or lower near the surface, optimizing carrier concentration and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Ga concentration in the p-type light absorption layer is reduced toward the n-type buffer layer, then defects in the surface are reduced and recombination centers are reduced, but the overall photoelectric conversion efficiency improvement is limited
Solution Approach 1:
The patent applies local quality by creating a gradient composition structure where the Cu/(Ga+In) ratio varies through the thickness of the light absorption layer. The surface region has lower Cu content (0.80-0.95) to reduce defects and recombination centers, while the bulk maintains higher Cu content (0.95-1.05) to preserve p-type polarity and photoelectric conversion efficiency. This spatial variation in composition allows simultaneous optimization of both surface quality and bulk electrical properties.
2Reliability
If the Cu to Group III elements ratio is set at 1.0 or higher, then the p-type polarity is maintained, but defects increase and photoelectric conversion efficiency is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Cu/(Ga+In) atomic ratio within specific ranges (0.80-0.95 at the surface, 0.95-1.05 in the bulk). This quantitative parameter optimization allows the material to maintain p-type polarity while minimizing defect formation. The specific ratio ranges represent optimized parameters that balance electrical properties with structural quality.
3Reliability
If the overall Cu to Group III elements ratio in the entire light absorption layer is increased, then p-type characteristics are improved, but recombination centers increase near the buffer layer interface
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through a composition gradient. The region near the buffer layer interface maintains lower Cu content (0.80-0.95 ratio) to minimize recombination centers, while the overall layer average maintains higher Cu content (0.95-1.05 ratio) to ensure p-type characteristics. This spatial differentiation allows simultaneous optimization of interface quality and bulk electrical properties.
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 configuration enhances photoelectric conversion efficiency by maintaining semiconductor characteristics while reducing recombination centers and improving electric properties, resulting in higher efficiency compared to conventional designs.
Implementation Method 1
a p-type light absorption layer formed by a Group I-III-VI 2 compound arranged on the first electrode layer... the atomic ratio of Cu over the Group III elements in the entire p-type light absorption layer is 0.86 to 0.98... improved photoelectric conversion efficiency can be attained
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
A thin-film solar cell comprising a substrate (11), a first electrode layer (12) arranged upon the substrate, a p-type light absorption layer (13) formed by a group I-III-VI2 compound arranged upon the first electrode layer (12), and an n-type second electrode layer (15) arranged upon the p-type light absorption layer (13). The p-type light absorption layer (13) includes Cu as a group 1 element and includes Ga and In as group III elements. The ratio of the atomic number between Cu and the group III elements in the entire p-type light absorption layer (13) is lower than 1.0; the ratio of the atomic number between Ga and the group III elements in the surface on the second electrode layer (15) side is no more than 0.13; and the ratio of the atomic number between Cu and the group III elements in the surface on the second electrode layer (15) side is at least 1.0.