9.4 Structure-function relationships in donor-acceptor systems
2 min read•Last Updated on July 25, 2024
Donor-acceptor systems are the backbone of organic photovoltaics. These two-component systems enable efficient charge separation, with donors providing electrons and acceptors creating an electron-deficient region. This setup promotes hole transfer and enhances photocurrent generation in organic solar cells.
HOMO-LUMO energy levels are crucial for solar cell efficiency. They determine open-circuit voltage and charge transfer efficiency. Tuning these levels allows optimization of both voltage and charge transfer, while proper orbital overlap enhances charge separation and overall device performance.
Fundamentals of Donor-Acceptor Systems
Donor-acceptor systems in photovoltaics
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Hole delocalization as a driving force for charge pair dissociation in organic photovoltaics ... View original
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Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original
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Energetics of charges in organic semiconductors and at organic donor–acceptor interfaces ... View original
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Top images from around the web for Donor-acceptor systems in photovoltaics
Hole delocalization as a driving force for charge pair dissociation in organic photovoltaics ... View original
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Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original
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Energetics of charges in organic semiconductors and at organic donor–acceptor interfaces ... View original
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Hole delocalization as a driving force for charge pair dissociation in organic photovoltaics ... View original
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Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original
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Two-component system in organic photovoltaics enables efficient charge separation and facilitates electron transfer from donor to acceptor
Donor materials (conjugated polymers or small molecules) provide electron-rich environment while acceptor materials (fullerene derivatives or non-fullerene acceptors) create electron-deficient region
Promotes hole transfer from acceptor to donor enhancing photocurrent generation in organic solar cells
System architecture optimizes charge separation and transport improving overall device efficiency
HOMO-LUMO levels for solar efficiency
HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) energy levels determine key performance parameters
Open-circuit voltage (VOC) correlates with energy difference between donor HOMO and acceptor LUMO (VOC ∝ (HOMOdonor - LUMOacceptor))
Charge transfer efficiency depends on energy offset between donor LUMO and acceptor LUMO with optimal LUMO-LUMO offset of 0.3-0.5 eV
Cascading energy levels (Donor HOMO > Donor LUMO > Acceptor LUMO > Acceptor HOMO) ensure efficient charge separation and transport
Tuning HOMO-LUMO levels allows optimization of both VOC and charge transfer efficiency
Orbital overlap for charge separation
Molecular orbital overlap determines electronic coupling strength between donor and acceptor influencing charge transfer rate
Charge transfer states form during electron transfer with binding energy affecting separation efficiency
Delocalization of charge transfer states energetic disorder at donor-acceptor interface and local electric fields impact charge separation
Marcus theory of electron transfer describes charge transfer rate dependence on reorganization energy and electronic coupling
Optimizing orbital overlap through molecular design enhances charge separation and overall device performance
Structural modifications of donor-acceptor cells
Non-fullerene acceptors (NFAs) offer advantages over fullerene acceptors:
Tunable energy levels enhance light absorption and reduce voltage losses
High-performance NFA examples include ITIC derivatives and Y-series acceptors