2D Semiconductor Contacts for Fermi-Level-Pinned Solar Cell Junctions
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Solution Overview
Problem
Conventional methods face challenges in simultaneously achieving high-quality n-type and p-type doping in semiconductor materials like ZnTe, CdSe, CdTe, and HgCdTe, leading to difficulties in forming electron or hole ohmic contacts, which are critical for optoelectronic devices, and the Fermi level pinning effect exacerbates these issues.
Innovation Solution
Utilizing n-type or p-type two-dimensional (2D) materials to form p-n or n-p junctions within semiconductors, combined with indium tin oxide (ITO) to create ohmic contacts, leveraging the surface Fermi level pinning effect to build an electrical field for carrier extraction or injection in solar cells and photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional doping methods are used on group II-VI semiconductor materials, then p-type or n-type doping can be achieved in single materials, but simultaneous high-quality n-type and p-type doping cannot be achieved
Solution Approach 1:
The patent divides the semiconductor contact structure into separate n-type and p-type regions using different 2D materials. Specifically, it uses n-type MoO2 and p-type WSe2 as distinct contact layers on opposite sides of the semiconductor, allowing independent optimization of each doping type without the mutual interference that plagues conventional single-material doping approaches.
Solution Approach 2:
The patent employs composite 2D material structures combining different materials with complementary properties. The n-type MoO2 and p-type WSe2 form a composite contact system that leverages the advantages of each material: MoO2 provides excellent n-type doping and transparency, while WSe2 provides high-quality p-type doping and hole selectivity, achieving simultaneous high-quality doping that neither material could achieve alone.
2Reliability
If metal contacts are used on semiconductor interfaces with high density of states, then electrical contact can be established, but Fermi level pinning occurs which degrades contact quality
Solution Approach 1:
The patent introduces 2D materials (MoO2 and WSe2) as intermediary layers between the metal electrodes and the semiconductor bulk. These 2D materials serve as mediators that decouple the metal Fermi level from the semiconductor Fermi level, preventing direct Fermi level pinning while still enabling efficient charge transfer. The 2D materials' unique electronic structure allows them to act as buffer layers that filter out the harmful pinning effect.
Solution Approach 2:
The patent changes the fundamental parameter of the contact interface by replacing conventional metal-semiconductor direct contact with 2D material-mediated contact. This parameter change involves transitioning from a bulk metal contact to a two-dimensional material interface, which fundamentally alters the electronic structure and prevents Fermi level pinning while maintaining good electrical contact.
3Illumination intensity
If transparent contacts are used in solar cells, then light transmission is improved, but electrical conductivity may be compromised
Solution Approach 1:
The patent changes the material parameters by using 2D materials with inherently high carrier mobility and appropriate band alignments. The n-type MoO2 and p-type WSe2 both exhibit high electron and hole mobilities respectively, allowing them to maintain excellent electrical conductivity while remaining transparent to the relevant solar spectrum. This parameter change enables simultaneous optimization of both optical and electrical properties.
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
Enables high-efficiency bifacial thin-film solar cells with transparent non-metallic contacts, achieving record Voc and efficiency improvements by minimizing interfacial recombination and optimizing device design through work-function engineering and non-destructive characterization.
Implementation Method 1
take advantage of the surface Fermi level pinning effect to build an electrical field inside of a semiconductor to extract or inject carriers
Implementation Method 2
the ITO and the 2D materials (either n- or p-type) will form an ohmic contact through an n-n junction of an n-p tunnel junction
Implementation Method 3
provide sufficiently high electrical field inside the semiconductor to extract photogenerated carriers in solar cells and photodetectors
Data Source
AI summary
Contacts for solar cells and other optoelectronic devices are provided. Embodiments described herein take advantage of the surface Fermi level pinning effect to build an electrical field inside of a semiconductor to extract or inject carriers for solar cells, photodetectors, and light-emitting device applications. For example, n-type or p-type two-dimensional (2D) materials can be used in contact with an n-type semiconductor to form a “p-region” so that a p-n junction, or an i-n or n-n+ junction can be constructed. Similarly, n-type or p-type 2D materials can be used in contact with a p-type semiconductor to form an “n-region” so that an n-p junction, or an i-p or p-p+ junction can be constructed. These structures can provide sufficiently high electrical field inside the semiconductor to extract photogenerated carriers in solar cells and photodetectors or inject minority carriers for light-emitting devices.