SnO2 Surface Coating for Solid-State Solar Cell Efficiency
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Solution Overview
Problem
Solid-state dye-sensitized solar cells (SDSCs) using SnO2 as the n-type semiconductor material exhibit remarkably low efficiency due to rapid electron recombination, which is not effectively addressed by previous solutions, and lack functional examples in literature, limiting their viability for large-scale applications.
Innovation Solution
A thin surface coating of a high band-gap material on SnO2 n-type semiconductor material is used to reduce recombination and enhance electron transfer, forming a solid-state p-n heterojunction with an organic p-type material, thereby improving the solar-to-electrical power conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If SnO2 is used as n-type semiconductor material in solid-state dye-sensitized solar cells, then the device structure is simplified and manufacturing is easier, but the conversion efficiency drops dramatically due to rapid electron recombination
Solution Approach 1:
The patent introduces TiO2 as an intermediary layer between the SnO2 electron transporter and the dye sensitizer. This TiO2 intermediate layer mediates the electron transfer process, preventing direct recombination of electrons with the oxidized dye while maintaining the beneficial low-conduction-band properties of SnO2 for electron injection. The intermediary layer thus resolves the contradiction by enabling both the ease of using SnO2 and the efficiency of electron transfer.
Solution Approach 2:
The patent creates a composite electron transporter system combining SnO2 and TiO2 materials. The composite structure leverages the low conduction band of SnO2 for efficient electron injection and the high electron mobility and stability of TiO2 to suppress recombination. This composite material approach allows the device to achieve both manufacturing simplicity and high conversion efficiency.
2Productivity
If the conduction band of the oxide is dropped to enable more efficient electron transfer from low band gap sensitizers, then the breadth of solar light harvesting increases, but electron recombination becomes more problematic
Solution Approach 1:
The TiO2 intermediate layer acts as a mediator that decouples the two conflicting requirements. It allows the SnO2 to maintain its low conduction band for broad light harvesting while the TiO2 layer provides a stable platform for electron transfer that reduces recombination. The intermediary thus enables both broad spectral response and stable electron transfer.
3Loss of energy
If a surface coating of high band-gap material is applied on SnO2 to reduce recombination, then the conversion efficiency increases significantly, but the device structure and manufacturing process become more complex
Solution Approach 1:
The patent applies the high band-gap TiO2 coating locally on the surface of the SnO2 particles rather than throughout the bulk material. This local quality approach allows the bulk SnO2 to maintain its beneficial low conduction band properties for electron injection, while only the surface region has the modified properties needed to suppress recombination. This resolves the contradiction by achieving high efficiency without requiring complete structural transformation.
Solution Approach 2:
The patent changes the band-gap parameter of the SnO2 surface by coating it with TiO2. This parameter change at the surface level modifies the electronic structure to reduce recombination, while the bulk SnO2 parameters remain unchanged to maintain efficient electron injection. The selective parameter modification resolves the efficiency-complexity contradiction.
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 approach significantly increases the overall conversion efficiency of SnO2-based SDSCs to be over 30 times that of uncoated devices, rivaling the efficiency of TiO2-based SDSCs, making them viable for commercial applications.
Implementation Method 1
said n-type material comprises SnO2 having at least one surface-coating of a surface coating material having a conduction band edge closer to vacuum level and/or a higher band-gap than SnO2
Implementation Method 2
Photo-excitation of the sensitizer leads to the transfer (injection) of electrons from the excited dye into the conduction band of the TiO2. These photo-generated electrons are subsequently transported to and collected at the anode.
Implementation Method 3
The oxidized dye is regenerated via hole-transfer to the redox active medium with the holes being transported through this medium to the cathode
Data Source
AI summary
The present invention provides a solid-state p-n heterojunction comprising a p-type material in contact with an n-type material wherein said n-type material comprises SnO2 having at least one surface-coating of a surface coating material having a higher band-gap than SnO2 and/or a conduction band edge closer to vacuum level than SnO2, such as MgO. The invention also provides optoelectronic devices such as solar cells or photo sensors comprising such a p-n heterojunction, and methods for the manufacture of such a heterojunction or device.