Tandem Solar Cell Oxide Interconnect for Low-Loss Subcell Contact
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Solution Overview
Problem
Current multi-junction photovoltaic cells face challenges with high material and manufacturing costs, as well as limitations in subcell interconnection, including parasitic absorption, suboptimal reflectance, and shunt paths due to surface roughness in conventional interconnection systems.
Innovation Solution
A two-terminal tandem photovoltaic cell design that eliminates conventional interconnection layers by using a wide bandgap oxide conductor, such as titanium dioxide, between a perovskite top subcell and a silicon bottom subcell, facilitating direct contact and ohmic conduction without the need for high-temperature processing or toxic gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional tunnel junctions with heavily doped layers are used for subcell interconnection, then electrical conduction is facilitated, but high-temperature processing above 800°C and toxic gases are required
Solution Approach 1:
The patent changes the material composition and doping parameters of the interconnection layer, transitioning from heavily doped amorphous silicon requiring 800°C processing to a titanium oxide-based layer that achieves adequate conductivity at lower temperatures through controlled oxygen vacancies and doping with elements like nitrogen or carbon
Solution Approach 2:
The patent replaces expensive and complex tunnel junction structures with a simpler, cheaper titanium oxide-based interconnection layer that can be deposited using low-cost techniques such as atomic layer deposition or sputtering, eliminating the need for costly high-temperature furnaces and toxic doping gases
2Device complexity
If transparent conductive oxide layers like ITO are used for subcell interconnection, then manufacturing complexity is reduced, but parasitic absorption and suboptimal reflectance occur
Solution Approach 1:
The patent creates a composite interconnection layer combining titanium oxide with doping elements such as nitrogen, carbon, or hydrogen, which modifies the optical properties to reduce parasitic absorption in the visible spectrum while maintaining electrical conductivity, achieving a balance between optical transparency and electrical function
Solution Approach 2:
The patent optimizes the local optical and electrical properties of the interconnection layer by controlling the doping concentration and distribution, creating regions with tailored properties that simultaneously minimize parasitic absorption and maintain adequate electrical conductivity for carrier transport
3Reliability
If conventional interconnection layers are used, then subcell connection is achieved, but surface roughness causes shunt paths and reduced efficiency
Solution Approach 1:
The patent introduces a titanium oxide-based interconnection layer as an intermediary between the perovskite and silicon subcells that provides a chemically stable and physically smooth interface, preventing direct contact between incompatible surfaces and eliminating shunt paths while facilitating controlled carrier transport
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 design achieves higher efficiency and reduced costs by enabling direct contact between subcells with low parasitic absorption and improved reflectance, while maintaining stability and simplicity in processing, resulting in efficiencies up to 23.2% under simulated sunlight.
Implementation Method 1
facilitating direct contact and ohmic conduction without the need for high-temperature processing or toxic gases
Implementation Method 2
Each subcell may be optimized to a specific section of the spectrum
Data Source
AI summary
Increasing the power conversion efficiency of silicon (Si) photovoltaics is a key enabler for continued reductions in the cost of solar electricity. Disclosed herein is a multi-junction photovoltaic cell that does not utilize a conventional interconnection layer and instead places a wide bandgap oxide conductor, for example, a metal oxide such as TiO2, between a top light absorption layer having a relatively large bandgap and a bottom light absorption layer having a relatively small bandgap. The advantageous omission of a conventional interconnection layer between the two subcells is enabled by low contact resistivity between the top and bottom light absorbing layers provided by the wide bandgap oxide conductor. The absence of the conventional interconnect between the subcells significantly reduces both optical losses and processing steps. The disclosed photovoltaic cell may thus enable low-cost, high-efficiency multi-junction devices through less complex manufacturing processes and lower material costs.