CIGS PN Junction Composition Without Selenization or Cd Buffer Layers
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Solution Overview
Problem
Conventional CIGS photodiode elements require selenization treatment and Cd-containing buffer layers, leading to inefficiencies and environmental concerns, with defects in the i-type CIGS semiconductor thin film layer affecting the formation of proper ohmic contact and reducing photoelectric conversion efficiency.
Innovation Solution
A PN junction is developed without selenization treatment, using n-type CIGS semiconductor thin film layers and a p-type CIGS semiconductor thin film layer with specific Cu to In molar ratios, along with a molybdenum compound layer and light converting thin film layer, to enhance light absorption and carrier transportation, eliminating the need for Cd and high-temperature reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selenization treatment is used to increase Se ratio in CIGS, then the surface bandgap is increased and open-circuit voltage is improved, but the reaction time is extended to 8-10 hours and the process complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-coating the substrate with a Cu-poor, In-rich buffer layer before depositing the CIGS absorber layer. This preliminary buffer layer preparation enables the subsequent CIGS deposition to proceed without requiring prolonged selenization treatment, as the buffer layer already provides the necessary Cu-deficient environment for forming the desired p-type CIGS structure with appropriate bandgap characteristics.
Solution Approach 2:
The patent changes the compositional parameters of the buffer layer by maintaining a Cu to In atomic ratio of 0.8-1.2 (which is Cu-deficient compared to stoichiometric CIGS). This parameter change in the buffer layer composition allows the system to achieve the required bandgap and voltage characteristics without extending the reaction time, as the buffer layer's Cu-poor composition directly influences the final CIGS layer properties during deposition.
2Reliability
If CdS is used as n-type compound semiconductor thin film layer for buffer layer, then bandgap matching with light absorbing layer is achieved, but environmental protection requirements are violated due to Cd content
Solution Approach 1:
The patent extracts and removes the harmful Cd element from the buffer layer material. Instead of using CdS, the invention employs a Cu-poor, In-rich CIGS-based buffer layer that is free of cadmium. This extraction of the toxic element eliminates the environmental harm while the buffer layer maintains its essential function of bandgap matching with the p-type CIGS absorber layer through its controlled compositional ratio.
Solution Approach 2:
The patent uses a composite CIGS-based buffer layer material with specific compositional ratios (Cu to In atomic ratio of 0.8-1.2) that combines the benefits of bandgap matching and environmental friendliness. This composite material approach replaces the traditional CdS while maintaining the necessary optical and electrical properties through the tailored CIGS composition, eliminating cadmium's environmental harm.
3Reliability
If Cu to In molar ratio in p-type CIGS is increased to improve photoelectric conversion, then photoelectric conversion efficiency is improved, but manufacturing precision control becomes more difficult
Solution Approach 1:
The patent applies preliminary action by pre-establishing the Cu-poor, In-rich buffer layer with a controlled Cu to In atomic ratio of 0.8-1.2 before depositing the p-type CIGS absorber layer. This preliminary buffer layer acts as a template that guides the subsequent CIGS deposition, ensuring that the absorber layer forms with the desired compositional characteristics and high photoelectric conversion efficiency without requiring extremely precise control during the deposition process itself.
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 solution results in a photodiode element with improved photoelectric conversion efficiency, reduced defects, and environmental friendliness, suitable for applications in biometrics, IR imaging, and X-ray cameras, while avoiding the limitations of selenization treatment and Cd usage.
Implementation Method 1
the p-type CIGS semiconductor thin film layer as a light absorbing layer
Implementation Method 2
an n-type CIGS semiconductor thin film layer as a buffer layer
Data Source
AI summary
The patent application relates to a PN junction as well as the preparation method and use thereof. Said PN junction comprises a p-type CIGS semiconductor thin film layer and an n-type CIGS semiconductor thin film layer, wherein the n-type CIGS semiconductor thin film layer comprises or consists essentially of elements Cu, In, Ga and Se, where the Cu to In molar ratio is within the range of 1.1 to 1.5, and has a chemical formula of Cu(InxGa1-x)Se2, where x is within the range of 0.6 to 0.9. The patent application further relates to a semiconductor thin film element comprising said PN junction, in particular a photodiode element, and a photoelectric sensing module comprising said semiconductor thin film element as well as the various uses thereof.