Controlled Molybdenum Selenide Thickness in Solar Cell Back Contacts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
It is challenging to control the thickness of molybdenum selenide layers in solar cells, as existing selenization processes often result in excessive film thickness, leading to higher sheet resistance and adhesion issues between the absorber layer and the molybdenum back electrode.
Innovation Solution
A method involving the formation of a distinct interface between a molybdenum layer and a molybdenum-containing layer, with the latter being selectively converted to a molybdenum selenide layer through a selenization process, while maintaining the molybdenum layer intact, using additives like oxygen and nitrogen to control the thickness and prevent diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selenization process is used to convert Mo layer to MoSe2, then MoSe2 layer is formed to provide ohmic contact, but the thickness of MoSe2 layer becomes difficult to control and often exceeds desired thickness
Solution Approach 1:
The molybdenum structure is divided into two distinct layers: a lower Mo layer (first molybdenum-containing layer) that remains unconverted and provides structural support, and an upper Mo-containing layer (second molybdenum-containing layer) that is selectively converted to MoSe2. This segmentation allows the selenization process to affect only the upper layer, achieving precise thickness control while maintaining reliable ohmic contact.
Solution Approach 2:
Different regions of the molybdenum structure are given different properties: the lower Mo layer maintains its metallic character for structural integrity and electrical conductivity, while the upper Mo-containing layer is converted to MoSe2 for optimal interface properties with the absorber layer. This local differentiation enables independent optimization of each layer's function.
2Reliability
If thicker MoSe2 layer is formed, then ohmic contact is established, but sheet resistance increases and device performance degrades
Solution Approach 1:
By dividing the Mo structure into two layers with only the upper layer undergoing selenization, the MoSe2 thickness is limited to the thickness of the upper Mo-containing layer. This prevents excessive MoSe2 formation and controls sheet resistance while maintaining sufficient thickness for ohmic contact.
3Reliability
If thicker MoSe2 layer is formed, then contact is established, but adhesion problems occur between absorber layer and Mo back electrode
Solution Approach 1:
The two-layer Mo structure with selective selenization of only the upper layer creates an optimal interface configuration. The thinner, controlled MoSe2 layer in the upper portion provides good contact with the absorber layer, while the underlying unconverted Mo layer maintains structural integrity and proper adhesion properties.
4Quantity of substance
If selenization process converts Mo layer to MoSe2, then MoSe2 material is produced for contact function, but degree of selenization and amount of Mo converted to MoSe2 becomes difficult to control
Solution Approach 1:
By separating the Mo structure into two layers where only the upper layer contains sufficient Mo for complete conversion to MoSe2, the process ensures controlled and complete selenization of the upper layer while leaving the lower layer unconverted. This segmentation provides precise control over the amount and degree of selenization.
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 allows for precise control of the molybdenum selenide layer thickness, improving device performance by reducing sheet resistance and enhancing adhesion, thereby producing solar cells with better efficiency and reliability.
Implementation Method 1
a selenization process that introduces selenium to the Mo-containing layer and converts the Mo-containing layer, but not the Mo layer, to a MoSe2 layer or other MoSe layer
Data Source
AI summary
A solar cell with a molybdenum back electrode layer and a molybdenum selenide ohmic contact layer over the molybdenum back electrode, is provided. The molybdenum selenide layer includes an accurately controlled thickness. A distinct interface exists between the molybdenum back electrode layer and the molybdenum silicide layer. The molybdenum silicide layer is produced by forming a molybdenum layer or a molybdenum nitride layer or a molybdenum oxide layer over an initially formed molybdenum layer such that an interface exists between the two layers. A selenization and sulfurization process is carried out to selectively convert the molybdenum-containing layer to molybdenum selenide but not the original molybdenum back electrode layer which remains as a molybdenum layer.