Multijunction Solar Cell Window Layer With Gradient Band Gap
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Solution Overview
Problem
Current multijunction solar cells face inefficiencies due to the design of the window layer, which can lead to minority carrier recombination and reduced photon conversion efficiency, particularly in III-V compound semiconductor devices.
Innovation Solution
The introduction of a window layer with a band gap greater than 2.6 eV, composed of materials like zinc selenide or oxidized InAIP, and the use of an oxidation stop layer to optimize the composition and thickness of the window layer, along with a passivation layer and an antireflective coating, to enhance light capture and reduce recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional window layer is used in the top solar subcell, then the structure is simpler and manufacturing is easier, but minority carrier recombination occurs and photoconversion efficiency is reduced
Solution Approach 1:
The patent employs composite material structures in the window layer, combining multiple semiconductor materials with different band gaps (e.g., AlInP, GaInP, InGaP) to create a gradient band gap structure. This composite approach prevents minority carrier recombination while maintaining structural integrity and optimizing photon absorption across different wavelength ranges, thereby resolving the contradiction between energy loss reduction and structural complexity.
Solution Approach 2:
The invention implements local quality optimization by varying the composition and band gap of the window layer at different positions. The window layer transitions from higher band gap materials near the emitter interface to lower band gap materials toward the outer surface, creating localized properties that prevent recombination at the interface while allowing photon transmission to deeper layers. This spatial variation in material quality resolves the contradiction by addressing recombination losses locally without requiring complete structural redesign.
2Loss of energy
If the window layer thickness is increased to improve light capture, then more photons are absorbed, but recombination losses increase and efficiency decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the window layer thickness to specific ranges (e.g., 50-200 nm) and varying the band gap parameters of constituent materials. By precisely controlling thickness and compositional parameters, the design achieves optimal balance between photon absorption and recombination prevention, allowing sufficient light capture while maintaining efficiency through controlled material properties rather than simply increasing thickness.
Solution Approach 2:
The invention introduces dynamic characteristics through gradient composition profiles in the window layer, where material composition continuously varies with depth. This dynamic structure allows the window layer to adapt its optical and electrical properties across its thickness, enabling efficient photon transmission in upper regions while maintaining recombination resistance at the emitter interface, thus resolving the thickness-efficiency contradiction.
3Loss of energy
If a window layer with higher band gap is used to reduce recombination, then recombination is minimized, but light absorption in the blue spectrum is reduced
Solution Approach 1:
The patent resolves this contradiction by using composite materials with gradient band gaps in the window layer. The structure combines high band gap materials (AlInP, GaInP) near the emitter to prevent recombination with lower band gap materials toward the surface to absorb blue spectrum photons. This composite gradient structure simultaneously achieves recombination minimization and broad-spectrum light absorption, eliminating the trade-off between these two competing requirements.
Solution Approach 2:
The invention applies local quality principles by creating spatially varying band gap properties within the window layer. High band gap regions are localized at the emitter interface to suppress recombination, while lower band gap regions extend toward the surface to enhance blue light absorption. This local differentiation of material quality allows the window layer to perform both functions optimally in different spatial zones, resolving the contradiction between recombination prevention and light absorption.
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 significantly improves the photoconversion and photoelectric efficiency of multijunction solar cells by minimizing recombination and optimizing light absorption, leading to higher current generation and overall efficiency.
Implementation Method 1
The window layer is disposed between the surface of the solar cell and the emitter layer of the top solar subcell and is composed of a semiconductor material having a band gap greater than 2.6 eV
Implementation Method 2
an antireflective coating layer above the window layer of the top solar subcell
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A multijunction solar cell including a substrate and a top (or light-facing) solar subcell having an emitter layer, a base layer, and a window layer adjacent to the emitter layer, the window layer composed of a material is specified such that the material is optically transparent, has a band gap of greater than 2.6 eV, and includes an appropriately arranged multilayer antireflection coating so as to increase the short circuit current in the top solar subcell.