CdTe Absorber Finger Structures for Back Contact
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Solution Overview
Problem
The existing contact between the cadmium telluride p-type absorber layer and the back contact layer in cadmium telluride-based photovoltaic devices results in reduced energy conversion efficiency and increased device deterioration due to poor metal electrode contact.
Innovation Solution
The introduction of finger structures protruding from the cadmium telluride p-type absorber layer into the back contact layer, with an aspect ratio of 1 or greater and a height that is 20% to 200% of the absorber layer thickness, enhances the electrical contact by increasing the surface area and improving adhesion and dopant uptake.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a flat back contact layer is used in contact with the p-type absorber layer, then the device structure is simple, but the electrical contact is poor leading to reduced energy conversion efficiency
Solution Approach 1:
The invention transitions from a two-dimensional flat contact interface to a three-dimensional finger structure configuration. The finger structures protrude vertically from the absorber layer into the back contact layer, adding a depth dimension to the contact interface. This dimensional change increases the contact surface area and improves electrical connection without significantly complicating the overall device structure.
Solution Approach 2:
The back contact interface is segmented into multiple discrete finger structures rather than a continuous flat layer. These finger structures are distributed across the back contact area, creating multiple localized contact points that collectively improve electrical connection while maintaining structural simplicity.
2Reliability
If metal electrodes are used for back contact, then the electrical conductivity is high, but the contact with p-type layer is poor especially with cadmium telluride
Solution Approach 1:
The finger structures extend vertically into the back contact layer, creating a three-dimensional contact geometry that enhances the interaction between the metal electrode and p-type absorber layer. This increased contact depth and surface area compensate for the inherent contact incompatibility between metal electrodes and cadmium telluride.
Solution Approach 2:
The invention changes the geometric parameters of the contact interface by creating finger structures with specific aspect ratios (1 or greater) and heights (20% to 200% of absorber layer thickness). These parameter changes optimize the contact characteristics between dissimilar materials, improving electrical connection despite material incompatibility.
3Reliability
If the finger structures have high aspect ratio and significant height, then the surface area and adhesion are improved, but the manufacturing precision requirements increase
Solution Approach 1:
The invention defines specific parameter ranges for the finger structures: aspect ratio of 1 or greater, and height of 20% to 200% of the absorber layer thickness. These parameter specifications optimize adhesion and electrical contact while providing clear manufacturing targets that balance performance requirements with manufacturability.
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 leads to lower series resistance, higher energy conversion efficiency, and extended device lifetime by maximizing the interaction between the p-type absorber layer and the back contact.
Implementation Method 1
The introduction of finger structures protruding from the cadmium telluride p-type absorber layer into the back contact layer, with an aspect ratio of 1 or greater and a height that is 20% to 200% of the absorber layer thickness, enhances the electrical contact by increasing the surface area
Implementation Method 2
CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy to electricity. The junction of the n-type layer and the p-type absorber layer is generally responsible for the generation of electric potential and electric current when the CdTe PV module is exposed to light energy, such as sunlight. Specifically, the cadmium telluride (CdTe) layer and the cadmium sulfide (CdS) form a p-n heterojunction
Data Source
AI summary
Thin film photovoltaic devices that include a transparent substrate; a transparent conductive oxide layer on the transparent substrate; a n-type window layer on the transparent conductive oxide layer; a p-type absorber layer on the n-type window layer; and, a back contact on the p-type absorber layer are provided. The p-type absorber layer comprises cadmium telluride, and forms a photovoltaic junction with the n-type window layer. Generally, the p-type absorber layer defines a plurality of finger structures protruding from the p-type absorber layer into the back contact. The finger structures can have an aspect ratio of about 1 or greater and/or can have a height that is about 20% to about 200% of the thickness of the p-type absorber layer. Methods of forming such finger structures protruding from a back surface of the p-type absorber layer are also provided.