Charging Solar Cell Passivation Layers to Reduce Recombination
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Solution Overview
Problem
Conventional solar cells face efficiency losses due to surface recombination, particularly in thinner wafers, where photo-generated carriers recombine at the back surface, and existing passivation layers like silicon nitride are not suitable for both N-type and P-type semiconductor materials, leading to parasitic shunting and increased costs with two-layer stack structures.
Innovation Solution
A system and method for charging a passivation layer with a positive or negative charge using a dielectric material like silicon nitride, allowing for field-effect passivation, where the layer can be charged during or after deposition, and integrated into existing PECVD systems, using a combination of RF and DC power to generate a plasma and apply a voltage pulse for charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional passivation layer like silicon nitride is used, then surface recombination is reduced, but parasitic shunting occurs in P-type semiconductor material
Solution Approach 1:
The patent applies a voltage pulse to the passivation layer during or after deposition to change its electrical charge state. This parameter change transforms the passivation layer from a neutral or positively charged state to a negatively charged state, which repels electrons (minority carriers in P-type material) and prevents parasitic shunting while maintaining surface recombination reduction
Solution Approach 2:
The charging process is performed during or immediately after the deposition process, before the solar cell undergoes subsequent manufacturing steps. This preliminary action ensures the passivation layer is properly charged to prevent parasitic shunting before any high-temperature processing or metal contact formation that could otherwise induce shunting effects
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 surface recombination by accumulating majority carriers and repelling minority carriers, enhancing solar cell efficiency without the need for heavy doping or additional layers, thus improving the cost-effectiveness and performance of solar cells.
Implementation Method 1
typically applied using a process known as plasma-enhanced chemical vapor deposition ('PECVD')
Implementation Method 2
Gas is injected into the chamber and a plasma is generated using the gas
Implementation Method 3
The solar cell is positioned in a chamber and in electrical communication with an electrode... a pulse is applied to charge the layer
Data Source
AI summary
Systems and methods of the present invention may be used to charge a layer (such as a passivation layer and/or antireflective layer) of a solar cell (e.g., wafer) with a positive or negative charge. The layer may retain the charge to improve operation of the solar cell. The charged layer may include any suitable dielectric material capable of retaining either a negative or a positive charge. Systems and methods of the present invention permit in-situ charging of a layer. Charging of a layer may be accomplished during or after deposition of the layer including after completing the whole solar cell process, in other words, on a finished cell.