Sputtering Target with Na2S for Stable Cu-Ga Film Deposition
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Solution Overview
Problem
The sputtering method for forming a Cu—In—Ga—Se quaternary alloy film in solar cells faces challenges in adding Na due to its low melting and boiling points and high reactivity, making it difficult to produce a sputtering target that effectively incorporates Na into the film.
Innovation Solution
A sputtering target with a composition of 20 to 40 at% Ga, 0.05 to 2 at% Na, and 0.025 to 1.0 at% S, where Na is added in a compound state as Na2S dispersed in a Cu—Ga matrix, allowing for stable direct-current sputtering and improved power generation efficiency, is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal Na is added to the sputtering target to improve power generation efficiency, then the power generation efficiency of the light absorbing layer is improved, but the production of the sputtering target becomes extremely difficult due to Na's low melting and boiling points and high reactivity
Solution Approach 1:
The patent changes the physical and chemical state of sodium from metallic form to compound form (Na2S). By converting Na to Na2S, the material achieves stable incorporation into the sputtering target while maintaining the beneficial electrical properties of sodium that improve power generation efficiency. This parameter change resolves the contradiction by making the material manufacturable without sacrificing its functional benefits.
Solution Approach 2:
The patent creates a composite sputtering target containing Cu, Ga, and Na2S in specific compositional ratios. This composite structure allows the Na2S to be stably embedded within the Cu-Ga matrix, preventing the issues associated with pure metal Na while still achieving the desired electrical conductivity and power generation efficiency improvements in the resulting film.
2Reliability
If Na is added to achieve high power generation efficiency, then the electrical properties of the light absorbing layer are improved, but film separation and oxygen incorporation occur during sputtering
Solution Approach 1:
Na2S acts as an intermediary compound that mediates between the requirements for electrical conductivity (provided by Na) and film stability (preventing separation and oxygen incorporation). The Na2S compound releases sodium atoms during sputtering in a controlled manner, ensuring uniform distribution without causing the harmful effects associated with adding pure metal Na.
Solution Approach 2:
By changing sodium's chemical state from metallic to sulfide compound, the patent controls the release and distribution of sodium during the sputtering process. This parameter change prevents film separation and oxygen incorporation while maintaining the electrical properties necessary for high power generation efficiency.
3Productivity
If the sputtering speed is increased to improve productivity, then the film formation speed is improved, but the uniformity of in-plane distribution of film thickness cannot be ensured
Solution Approach 1:
The patent performs preliminary action by pre-incorporating Na2S into the sputtering target matrix before the actual film formation process. This preliminary incorporation ensures that sodium is uniformly distributed throughout the target material, which then translates to uniform sodium release during high-speed sputtering, maintaining film thickness uniformity even at increased productivity levels.
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 enables the formation of a Cu—Ga film with Na, enhancing power generation efficiency in solar cells by stabilizing the sputtering process and preventing film separation and oxygen incorporation, while maintaining mechanical strength and preventing abnormal discharge.
Implementation Method 1
a sputtering method for forming a light absorbing layer consisting of a Cu—In—Ga—Se quaternary alloy film has been proposed
Data Source
AI summary
[Problems to be Solved]To provide a sputtering target that is capable of forming a Cu—Ga film to which Na is favorably added by a sputtering method, and a method for producing the same.[Means to Solve the Problems]The sputtering target is provided wherein 20 to 40 at % of Ga, 0.05 to 2 at % of Na, and 0.025 to 1.0 at % of S are contained and a remaining portion has a component composition consisting of Cu and unavoidable impurities. Also, a method for producing the sputtering target includes the step of hot pressing a mixed powder of Na2S powder and Cu—Ga alloy powder or a mixed powder of Na2S powder, Cu—Ga alloy powder, and pure Cu powder in a vacuum atmosphere or an inert gas atmosphere or sintering a mixed powder of Na2S powder and Cu—Ga alloy powder or a mixed powder of Na2S powder, Cu—Ga alloy powder, and pure Cu powder by hot isostatic pressing.