Rear-Contact Heterojunction Cell with Interdigitated Metallization
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Solution Overview
Problem
The manufacture of heterojunction rear contact photovoltaic cells is complex and difficult to industrialize due to the need for multiple steps in existing methods, including photolithography and masking processes, which require two distinct amorphous silicon deposition steps.
Innovation Solution
A semiconductor device with a simplified manufacturing process using a single step for depositing doped amorphous silicon on the rear face and a single step for metallic material deposition for charge carrier collection, featuring an interdigitated metallization structure with aluminum and a hydrogenated amorphous silicon nitride anti-reflective layer, and utilizing laser annealing for localized P-type contact formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple photolithography and masking steps are used to create selective rear contacts, then contact selectivity is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The rear surface is segmented into distinct functional zones (N-type doped region and P-type doped region) that are created in separate processing steps. The N-type region is formed first through phosphorus diffusion, then the P-type region is formed through aluminum diffusion, allowing selective contact formation without requiring complex photolithography masking sequences.
Solution Approach 2:
The N-type doped region is created in advance before the P-type doped region is formed. This preliminary action allows the subsequent P-type diffusion to be performed without interfering with the already-formed N-type contact, simplifying the overall process by eliminating the need for complex masking steps that would be required if both contacts were formed simultaneously.
2Reliability
If traditional front-face metal grids are used, then electrical contact is achieved, but light absorption is reduced due to shading
Solution Approach 1:
Instead of placing metal contacts on the front face where light enters, the invention inverts the contact location to the rear face of the cell. The front face is left entirely free of metal contacts, allowing maximum light absorption, while the rear face contains the N-type and P-type doped regions that provide electrical contact functionality without blocking incident light.
3Reliability
If conductive transparent oxide is used on the front face, then electrical conduction is achieved, but light absorption increases and cost increases due to rare materials
Solution Approach 1:
The invention eliminates the need for conductive transparent oxide on the front face by inverting the contact architecture to the rear face. Since no electrical conduction is needed on the front face, expensive and light-absorbing transparent conductive oxides are replaced with simple dielectric or amorphous silicon layers that do not absorb light and are less expensive.
4Reliability
If heterojunction contacts are used on the rear face, then open circuit voltage is improved and passivation is enhanced, but manufacturing steps increase
Solution Approach 1:
The invention creates heterojunction contacts by changing the doping type parameters of the silicon substrate at different rear surface regions. By introducing N-type phosphorus doping in one region and P-type aluminum doping in another region, heterojunctions are formed that enhance open circuit voltage and passivation, while the diffusion-based process keeps manufacturing steps manageable.
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 reduces the number of manufacturing steps, minimizes metal contact shading on the front face, eliminates the need for conductive transparent oxides, and maintains effective passivation, resulting in higher efficiency and easier industrial-scale production of photovoltaic cells with reduced ohmic losses.
Implementation Method 1
a photovoltaic cell is a semiconductor diode designed to absorb light energy and convert it into electrical energy
Implementation Method 2
the contact of each layer metallic with the substrate being ensured by laser annealing of the metallic layer at point locations
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a semiconductor device comprising: a crystalline semiconductor substrate (1) having a front face (1a) and a rear face (1b); a front passivation layer (3) placed on the front face (1a) of the substrate (1); a rear passivation layer (2) placed on the rear face (1b) of the substrate (1); a first metallization zone (10) placed on the rear passivation layer (2) and designed for collecting electrons; a second metallization zone designed for collecting holes, comprising: a surface portion (11) placed on the rear passivation layer (2); and an internal portion (12) passing through the rear passivation layer (2) and forming, in the substrate (1), a region in which the concentration of electron acceptors is greater than the rest of the substrate (1). The invention also relates to a module of photovoltaic cells using this device and to a process for manufacturing this device.