Silver Transparent Electrode Stack for High-Temperature Stability
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Solution Overview
Problem
Current transparent electrodes for photovoltaic cells lack a combination of low sheet resistance, high transparency, and stability at elevated temperatures, which are essential for efficient light transmission and subsequent layer deposition, particularly for CdTe devices where pinholes and electrical shorting are concerns.
Innovation Solution
A transparent electrode stack comprising a base layer of (oxi)nitride of silicon or aluminium, a layer of oxide of Zn and Sn, a separation layer, and a top layer of oxide of Zn, with a silver-based functional layer and a barrier layer, where the second dielectric layer includes ZnO:Al, providing improved heat treatability and optical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transparent electrode stack is designed with multiple layers to achieve low sheet resistance and high transparency, then the optical and electrical performance is improved, but the stability at elevated temperatures deteriorates due to pinholes and electrical shorting
Solution Approach 1:
The transparent electrode is divided into multiple functional layers including a lower anti-reflection layer with base layer, ZnSnOx layer, separation layer, and top layer; a silver-based functional layer; and an upper anti-reflection layer with barrier layer and top layer. Each layer serves specific functions to collectively achieve temperature stability while maintaining optical and electrical performance.
Solution Approach 2:
The electrode employs composite material structures such as ZnSnOx (zinc stannate oxide) combining zinc oxide and tin oxide, and ZnO:Al (aluminum-doped zinc oxide) in the barrier layer. These composite materials provide enhanced thermal stability, physical robustness, and electrical properties that individual materials cannot achieve alone.
2Manufacturing precision
If a smooth growth layer is provided to improve subsequent layer deposition and reduce pinholes, then the manufacturing quality is improved, but the sheet resistance increases
Solution Approach 1:
Different layers within the electrode stack have optimized local properties: the base layer and ZnSnOx layer provide smooth morphology for subsequent layer growth, while the silver-based functional layer and ZnO:Al barrier layer are optimized for low sheet resistance. This local optimization allows each layer to fulfill its specific function without compromising overall performance.
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 electrode stack achieves superior optical transparency, physical robustness, and stability at high temperatures, enhancing the growth of subsequent layers and reducing electrical shorting, leading to improved photovoltaic cell performance and efficiency.
Implementation Method 1
Sputter deposition is a Physical Vapour Deposition (PVD) technique frequently employed in the manufacture of photovoltaic devices. By non-reactive sputtering, a 'target' comprising the material to be deposited, and a substrate (e.g. glass) are located in a sputtering chamber and an inert gas such as Argon is used to bombard the target. This action causes atoms and, or ions of the target material to be released which are then deposited on the substrate.
Implementation Method 2
The cells contain semiconductor materials exhibiting the photovoltaic effect and these are typically realised in solar panels comprising an array of cells.
Data Source
AI summary
A transparent conducting electrode is disclosed having a coating stack structure, including a dielectric layer, a functional layer based on silver, a barrier layer and a further dielectric layer. The unique coating stack offers an electrode having requisite electrical properties and the ability to withstand elevated temperatures associated with further treatment, e.g. in the manufacture of photovoltaic devices.