Photocatalyst Selective Contacts for Charge Separation
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Solution Overview
Problem
Photocatalytic systems face inefficiencies due to poor charge-separation processes and high recombination rates of electrons and holes, which are exacerbated by the nanoscale geometry of light absorbers and multi-redox reactions at surface sites, making it challenging to implement selective contacts effectively.
Innovation Solution
A system comprising a semiconductor with selective contacts, including an electron transport layer (ETL) and a hole transport layer (HTL), which are attached to the semiconductor to physically separate charge carriers, reducing recombination and enhancing the photocatalytic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If selective contacts (ETL and HTL) are attached to the semiconductor, then charge separation is improved and recombination is reduced, but device complexity increases
Solution Approach 1:
The system divides the semiconductor surface into distinct functional zones by attaching separate electron transport layers (ETL) and hole transport layers (HTL) as selective contacts. This segmentation allows independent optimization of electron and hole extraction pathways, improving charge separation efficiency while managing complexity through modular layer integration
Solution Approach 2:
The ETL and HTL act as intermediary layers between the semiconductor and the external circuit. These intermediate contacts facilitate selective charge carrier extraction while blocking the opposite carriers, thereby reducing recombination. The mediators enable efficient charge separation without requiring direct complex interactions between the semiconductor and electrolyte
2Use of energy by moving object
If the semiconductor thickness is increased to absorb more light, then light absorption improves, but charge carrier recombination increases due to longer diffusion paths
Solution Approach 1:
The semiconductor is functionally segmented into regions with different primary carriers (electron-rich and hole-rich zones). By attaching selective ETL and HTL contacts at specific locations, the system creates dedicated extraction pathways that reduce the effective diffusion distance for charge carriers, thereby reducing recombination losses even in thicker semiconductors that absorb more light
Solution Approach 2:
Different regions of the semiconductor are equipped with different selective contacts optimized for their local charge carrier type. The ETL is positioned where electrons are the primary carriers, while HTL is positioned where holes dominate. This local optimization ensures efficient charge extraction throughout the entire semiconductor volume, balancing light absorption with reduced recombination
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 system improves charge separation and increases the efficiency of photocatalytic reactions by effectively blocking the exit of one type of charge carrier while facilitating the exit of the other, leading to enhanced hydrogen production from water or alcohol.
Implementation Method 1
The efficiency of photocatalytic systems is limited by poor charge-separation processes and by the recombination of electrons and holes before they have participated in the reaction
Implementation Method 2
These electrons and holes are photogenerated in a semiconductor, in which the energetic position of the band gap will largely determine the final energy of the carriers
Implementation Method 3
One of the most used ways in photocatalysis is through the creation of energy barriers, which allow the passage of one type of charge carrier, while blocking the other, physically separating electrons and holes
Implementation Method 4
Photocatalysis is defined as the acceleration of chemical reactions under illumination and in the presence of a photocatalyst
Data Source
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AI summary
The present disclosure relates to a system suitable for photocatalysis comprising a semiconductor and selective contacts, the selective contacts being at least two, wherein the selective contacts are attached to the semiconductor; and the selective contacts comprise an electron transport layer and a hole transport layer. It also relates to a method to produce a system suitable for photocatalysis comprising the steps of: providing a sol-gel precursor of the semiconductor; dissolving the sol-gel precursor in a polar solvent; adding acid to the dissolution and stirring the dissolution to obtain a sol of the semiconductor; depositing the semiconductor in a suitable substrate; submitting the deposited semiconductor to a temperature of at least 300 °C for at least 1 hour to obtain a thin film of semiconductor; depositing on the semiconductor an electron transport layer and/or a hole transport layer. The present disclosure also relates to a method to obtain hydrogen from water or alcohol comprising the steps of contacting the system defined with water and/or alcohol, and irradiating the system as defined with light.