Interlayers for Triplet Exciton Transfer in Solar Cells
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Solution Overview
Problem
Conventional solar cells, particularly those using silicon, face inefficiencies due to thermalization losses, where excess photon energy is lost as heat rather than electrical energy, and coupling singlet exciton fission materials with silicon has proven challenging, limiting the potential for improved energy conversion efficiency.
Innovation Solution
The use of thin interlayers, such as charge transfer and passivation layers, to facilitate efficient transfer of triplet excitons from singlet exciton fission materials like tetracene to inorganic semiconductors, utilizing strategically positioned highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels to minimize energetic losses and enhance energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional single junction silicon solar cells are used, then manufacturing simplicity is maintained, but thermalization losses occur where excess photon energy is lost as heat instead of electrical energy
Solution Approach 1:
The patent introduces an organic singlet exciton fission layer as an intermediary between the incident light and the silicon solar cell. This layer absorbs high-energy photons and converts them into multiple lower-energy excitons through singlet exciton fission, which then transfer energy to the silicon cell. This mediator approach allows reduction of thermalization losses without requiring complex multi-junction structures, resolving the contradiction between energy loss reduction and device complexity.
2Loss of energy
If singlet exciton fission material is coupled directly to silicon, then energy conversion efficiency may improve, but the coupling proves challenging and difficult to achieve
Solution Approach 1:
The patent employs an organic singlet exciton fission layer as a mediator between light and the silicon cell. This layer is specifically designed to absorb high-energy photons and generate multiple excitons through singlet exciton fission, then transfer this energy to the silicon cell. This intermediary approach simplifies the coupling process compared to direct coupling attempts, while still achieving improved energy conversion efficiency.
3Power
If high energy photons are absorbed by silicon, then charge generation occurs, but excess photon energy is rapidly lost via thermalization as heat
Solution Approach 1:
The patent converts the harmful effect of excess photon energy (which causes thermalization losses) into a beneficial effect. The organic singlet exciton fission layer absorbs these high-energy photons and uses the excess energy to generate multiple excitons through singlet exciton fission. This transforms what would be wasted heat into useful electrical energy, increasing charge generation while reducing energy loss.
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 enables improved energy conversion efficiency by effectively transferring triplet excitons from singlet fission materials to inorganic semiconductors, reducing thermalization losses and enhancing the performance of solar cells.
Implementation Method 1
The triplet transfer mechanism proceeds via the formation of a charge transfer (CT) state intermediate, via the charge transfer (CT) interlayer. The CT state is the electron-hole state existing between the CT layer and the inorganic semiconductor.
Implementation Method 2
transferring energy from the triplet excitons produced by the singlet fission layer to the inorganic semiconductor substrate via a charge transfer layer
Implementation Method 3
Singlet exciton fission is a spin-allowed energy down-conversion process in which one spin-singlet state (in this case, an exciton or electron-hole pair) is converted into two lower-energy spin-triplet states.
Implementation Method 4
surface traps of the inorganic semiconductor can be passivated using an ultrathin passivation interlayer, which can be deposited directly on the inorganic semiconductor
Data Source
AI summary
Compositions and mechanisms for the transfer of spin-triplet excitons from a singlet exciton fission material (e.g., tetracene) to an inorganic semiconductor (e.g., n-doped silicon) are provided. The compositions include one or more interlayers, including a charge transfer interlayer (e.g., zinc phthalocyanine), and, optionally, a passivation interlayer (e.g., hafnium oxide, HfO2). The triplet transfer mechanism proceeds via the formation of a charge transfer intermediate state. The transition to the intermediate state is energetically favored by strategically positioned HOMO and/or LUMO levels of the charge transfer interlayer between the singlet fission layer and the inorganic semiconductor. The intermediate state is formed through a transition of either the electron or the hole of the triplet exciton in the charge transfer interlayer (depending, at least in part, on the relative positions of the energy levels) to the conduction or valence band of the inorganic semiconductor, respectively. Methods of forming the compositions are also disclosed.