CVD and Sputtered Zinc Oxide Layers for Photovoltaic Stability
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Solution Overview
Problem
Existing thin-film photovoltaic devices with CIS type absorber layers face challenges in achieving optimal electrical performance and damp-heat stability, particularly due to degradation issues with CVD deposited zinc oxide layers.
Innovation Solution
A process involving a first layer of chalkopyrite semiconductor, a second layer of intrinsic zinc oxide by chemical vapor deposition, and a third layer of n-type zinc oxide deposited by a method other than CVD, such as sputtering, with an optional cadmium-free buffer layer, to enhance electrical properties and damp-heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CVD deposited zinc oxide layer is used in thin-film photovoltaic devices, then good electrical performance can be achieved, but the device shows relatively large degradation in damp-heat tests
Solution Approach 1:
The zinc oxide layer is segmented into two distinct layers: a first zinc oxide layer deposited by CVD to provide good electrical performance, and a second zinc oxide layer deposited by sputtering to provide damp-heat stability. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between electrical performance and damp-heat stability.
Solution Approach 2:
Different regions of the zinc oxide structure are given different properties: the first layer (CVD) has properties optimized for electrical conductivity and charge transport, while the second layer (sputtering) has properties optimized for environmental stability and resistance to moisture. This local differentiation of quality allows the overall structure to satisfy both contradictory requirements.
2Reliability
If a buffer layer of cadmium sulphide is used on the CIS type layer, then electrical performance is improved, but cadmium usage increases
Solution Approach 1:
The harmful substance (cadmium) is extracted and removed from the device structure. The invention achieves this by eliminating the cadmium sulphide buffer layer and replacing it with a zinc oxide-based layer structure that provides equivalent or superior electrical performance without cadmium contamination, thus resolving the contradiction between electrical performance and cadmium usage.
Solution Approach 2:
The material composition parameter is changed from cadmium-based to zinc-based. By substituting cadmium sulphide with zinc oxide layers, the invention maintains the functional requirements for electrical performance while changing the chemical composition to eliminate toxic cadmium, resolving the contradiction between performance and substance loss.
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 combination of CVD deposited intrinsic zinc oxide and sputter deposited doped zinc oxide layers improves electrical performance and increases damp-heat stability, achieving comparable or better results than conventional technologies while minimizing cadmium usage.
Implementation Method 1
both zinc oxide layers are deposited by chemical vapour deposition ('CVD'). In a CVD process, the substrate is exposed to a chemically reactive vapour composition, wherein the reaction taking place on the substrate surface produces the desired deposit as a film
Implementation Method 2
a 600-800 nm thick n-type ZnO layer is deposited by DC magnetron sputtering from a ZnO-Al2O3 target
Data Source
AI summary
A thin-film photovoltaic device and a process of making such a device, the device comprising a first layer of a chalkopyrite semiconductor of a first doping type; a second layer of intrinsic zinc oxide deposited by chemical vapor deposition; a third layer of zinc oxide semiconductor of a second doping type opposite to the first doping type and deposited by a method other than chemical vapor deposition; and wherein the second layer is arranged between the first and third layers.