Solar Cell Tunneling Junctions for Carrier Recombination Control
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Solution Overview
Problem
Current solar cells face challenges in achieving high energy-conversion efficiency and low temperature coefficients due to minority-carrier recombination at surfaces, particularly in homojunction cells, and scaling issues with MIS-based cells related to conductivity and stability of Cs-doped oxide layers.
Innovation Solution
A tunneling-junction based solar cell design incorporating a quantum-tunneling-barrier layer made of thin dielectric materials like silicon oxide, combined with graded-doping amorphous-Si layers for surface passivation and field effect enhancement, allowing for ultra-high open circuit voltage and efficient carrier collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick, heavily doped emitter layer is used in homojunction solar cells, then the electrical conductivity is improved, but minority-carrier recombination increases and surface passivation deteriorates
Solution Approach 1:
The emitter region is segmented into two distinct layers: a heavily doped emitter layer for electrical conductivity and an intrinsic or lightly doped tunneling layer for surface passivation. This segmentation allows each layer to optimize its function without compromising the other, resolving the contradiction between conductivity and recombination loss.
Solution Approach 2:
An intrinsic or lightly doped tunneling layer is introduced as an intermediary between the heavily doped emitter and the base layer. This intermediate layer provides excellent surface passivation by reducing minority-carrier recombination at the interface, while the heavily doped emitter layer beneath it maintains electrical conductivity through dopant diffusion.
2Loss of energy
If an intrinsic a-Si layer is inserted between the heavy doped a-Si layer and the c-Si base layer, then surface passivation is improved, but device complexity increases
Solution Approach 1:
The tunneling layer combines multiple functions into a single thin layer: it serves as a diffusion barrier to prevent dopant migration, provides surface passivation through hydrogenation of dangling bonds, and enables efficient carrier transport via quantum tunneling. This merging of functions reduces the need for additional separate layers, managing device complexity while achieving excellent surface passivation.
3Reliability
If an ultra-thin dielectric layer is used as a tunneling layer in MIS-based solar cells, then carrier tunneling efficiency is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise thickness parameters for the tunneling layer (1-10 nm range) to optimize the balance between carrier tunneling efficiency and manufacturing feasibility. By defining this specific parameter range, the invention enables efficient tunneling while maintaining compatibility with existing semiconductor fabrication processes that can control thin film deposition within this range.
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
The solution achieves ultra-high open circuit voltage and improved temperature coefficient performance while maintaining low series resistance and surface recombination velocity, enabling higher efficiency and scalability of solar cells.
Implementation Method 1
a tunneling junction structure that uses a dielectric material (e.g. silicon oxide) to form a tunneling layer
Implementation Method 2
A solar cell converts light into electricity using the photoelectric effect
Implementation Method 3
The a-Si layer also passivates the surface of the c-Si base layer by repairing the existing Si dangling bonds through hydrogenation
Data Source
AI summary
One embodiment of the present invention provides a tunneling junction based solar cell. The solar cell includes a base layer; a quantum-tunneling-barrier (QTB) layer situated adjacent to the base layer; an emitter; a surface field layer; a front-side electrode; and a back-side electrode.