CdTe Back Contact Interface via Plasma Cleaning and Oxide Passivation
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Solution Overview
Problem
The formation of efficient and stable ohmic contacts on p-type CdTe layers in photovoltaic devices is challenging due to incompatibility of the crystalline structure and manufacturing processes, leading to surface contamination and poor interfaces, which affects the device's performance and stability.
Innovation Solution
A process involving a cleaning and passivation step using plasma cleaning and oxygen exposure to prepare the absorber surface, followed by the deposition of a back contact layer, which forms a thin oxide layer that acts as a barrier and tunneling layer, improving the interface quality and reducing recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If known methods of removing contaminants from the semiconductor layer surface are used, then surface contamination is reduced, but grain boundaries and lattice structure of the crystals are negatively affected
Solution Approach 1:
The invention changes the chemical parameters of the cleaning solution by using a combination of organic and inorganic acids with specific concentration ratios. This optimized chemical composition enables effective contaminant removal while minimizing damage to the semiconductor crystal structure, resolving the contradiction between cleaning effectiveness and structural integrity
Solution Approach 2:
The cleaning solution is formulated as a composite of multiple acid components (organic and inorganic acids) working synergistically. This composite approach allows the solution to simultaneously dissolve organic contaminants and metal oxides while maintaining a milder overall effect on the crystal lattice compared to using strong single-component acids
2Use of energy by moving object
If the window layer is made thinner to allow maximum light to reach the absorber layer, then light absorption is improved, but the p-n junction robustness and shunt prevention are compromised
Solution Approach 1:
The invention optimizes the window layer thickness parameter to a specific range that balances optical transmission and electrical functionality. By precisely controlling the thickness parameter, the design achieves sufficient light transmission while maintaining adequate mechanical and electrical robustness of the p-n junction
3Reliability
If a metal contact with higher work function is used to avoid Schottky barrier formation, then ohmic contact stability is improved, but metal availability and cost are limited
Solution Approach 1:
The invention introduces an intermediary layer between the metal contact and the p-type semiconductor. This intermediate layer has a work function that bridges the gap between the metal and semiconductor, enabling stable ohmic contact to be formed with more readily available metals while avoiding the need for rare high-work-function metals
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 approach enhances the stability and efficiency of the photovoltaic device by improving the interface between the absorber and back contact layers, leading to increased open-circuit voltage, fill factor, and longer-term stability, while reducing copper diffusion and surface defects.
Implementation Method 1
A process involving a cleaning and passivation step using plasma cleaning
Implementation Method 2
oxygen exposure to prepare the absorber surface, followed by the deposition of a back contact layer, which forms a thin oxide layer
Data Source
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AI summary
Disclosed are methods for the surface cleaning and passivation of PV absorbers, such as CdTe substrates usable in solar cells, and devices made by such methods. In some embodiments, the method involves an anode layer ion source (ALIS) plasma discharge process to clean and oxidize a CdTe surface to produce a thin oxide layer between the CdTe layer and subsequent back contact layer(s).