Thin Film Solar Cell Voids Back Surface Reflector
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Solution Overview
Problem
CIS-based thin film solar cells face challenges in achieving high photovoltaic conversion efficiency due to the formation of voids during the selenization process, which reduces the contact area between the electrode and the p-type light absorption layer, and lack effective back surface reflection structures, limiting their performance compared to crystalline Si solar cells.
Innovation Solution
The formation of voids at the interface between the backside electrode layer and the p-type light absorption layer, with a contact ratio of 80% or less, and the use of a sulfur-passivated front surface, along with a gas-filled voids containing nitrogen, allows for a point contact structure and back surface reflector (BSR) functionality without an insulating film, enhancing light reflectance and reducing carrier recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous contact structure between the backside electrode and the p-type light absorption layer is formed, then the electrical connection is good, but the carrier recombination rate increases due to high dangling bond density at the contact interface
Solution Approach 1:
The patent applies segmentation by introducing voids to divide the continuous contact interface into discrete contact points between the backside electrode and the p-type light absorption layer. This segmentation reduces the total contact area while maintaining electrical connection, thereby lowering the overall carrier recombination rate at the interface.
Solution Approach 2:
The patent applies local quality by creating a non-uniform contact structure where voids are selectively formed at specific regions of the interface. This allows different areas to have different properties: contact regions provide electrical connection while void regions reduce recombination, optimizing both functions locally.
2Reliability
If the contact area between the backside electrode and the p-type light absorption layer is increased, then the electrical connection is improved, but the open circuit voltage decreases due to increased front surface recombination
Solution Approach 1:
The patent segments the contact interface by introducing voids, reducing the total contact area between the backside electrode and the p-type light absorption layer. This segmentation lowers the front surface recombination rate, thereby improving the open circuit voltage while maintaining sufficient electrical connection through the remaining contact points.
3Loss of energy
If an insulating film is formed between the semiconductor layer and the electrodes to realize point contact structure, then the carrier recombination rate is reduced, but the production process becomes complicated and the production cost increases
Solution Approach 1:
The patent applies self-service by utilizing the voids that are naturally formed during the selenization process of the CIS-based thin film solar cell. Instead of requiring an additional insulating film to create point contact, the voids themselves provide the necessary separation and recombination reduction, making the structure self-forming and eliminating extra production steps.
Solution Approach 2:
The patent converts the harmful effect of void formation (which was traditionally considered a defect reducing contact area) into a beneficial feature. The voids, instead of being eliminated, are utilized to create the desired point contact structure that reduces carrier recombination, turning a manufacturing defect into a performance-enhancing feature.
4Use of energy by moving object
If a BSR structure is implemented in CIS-based thin film solar cell, then the light absorption is improved, but the reflectance is low because the refractive index of the backside electrode material is similar to the semiconductor layer
Solution Approach 1:
The patent introduces voids filled with gas (having a refractive index of approximately 1.0) as an intermediary layer between the backside electrode and the p-type light absorption layer. This intermediary creates a larger refractive index contrast compared to direct metal-semiconductor contact, thereby enhancing the back surface reflectance and improving light absorption efficiency.
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 results in improved open circuit voltage and photovoltaic conversion efficiency by reducing the contact area and increasing internal reflectance, effectively mimicking the point contact and BSR structures seen in crystalline Si solar cells.
Implementation Method 1
the voids may be formed between the intermediate layer and the p-type light absorption layer... increasing internal reflectance
Implementation Method 2
the back surface internal reflectance is determined by the refractive index (N) of the semiconductor and the backside electrode
Implementation Method 3
the front surface of the p-type light absorption layer which faces the voids may also be passivated by sulfur
Implementation Method 4
a CIS-based thin film solar cell which uses a Group I-III-VI2 compound semiconductor of a chalcopyrite structure which contains Cu, In, Ga, Se, and S as a p-type light absorption layer
Data Source
AI summary
Disclosed is a thin-film solar cell which has a high photoelectric conversion efficiency and is provided with a substrate (1), a backside surface electrode layer (2) formed on the substrate (1), a p-type light-absorbing layer (3) formed on the backside surface electrode layer (2), and an n-type transparent conductive film (5) formed on the p-type light-absorbing layer (3). Voids (6) are formed at the interface of the backside surface electrode layer (2) and the p-type light-absorbing layer (3).