Delocalisation enables efficient charge generation in organic photovoltaics, even with little to no energetic offset

Abstract

Organic photovoltaics (OPVs) are promising candidates for solar-energy conversion, with device efficiencies continuing to increase. However, the precise mechanism of how charges separate in OPVs is not well understood because low dielectric constants produce a strong attraction between the charges, which they must overcome to separate. Separation has been thought to require energetic offsets at donor-acceptor interfaces, but recent materials have enabled efficient charge generation with small offsets, or with none at all in neat materials. Here, we extend delocalised kinetic Monte Carlo (dKMC) to develop a three-dimensional model of charge generation that includes disorder, delocalisation, and polaron formation in every step from photoexcitation to charge separation. Our simulations show that delocalisation dramatically increases charge-generation efficiency, partly by enabling excitons to dissociate in the bulk. Therefore, charge generation can be efficient even in devices with little to no energetic offset, including neat materials. Our findings demonstrate that the underlying quantum-mechanical effect that improves the charge-separation kinetics is faster and longer-distance hops between delocalised states, mediated by hybridised states of exciton and charge-transfer character.

References in corpus (20)

• The Role of Driving Energy and Delocalised States for Charge Separation in Organic Semiconductors
• Entropy and disorder enable charge separation in organic solar cells
• Does coherence enhance transport in photosynthesis?
• Molecular Response in One-Photon Absorption via Natural Thermal Light vs Pulsed Laser Excitation
• Noise-induced quantum coherence drives photocarrier generation dynamics at polymeric semiconductor heterojunctions
• Exciton Dynamics in Photosynthetic Complexes: Excitation by Coherent and Incoherent Light
• A multi-site variational master equation approach to dissipative energy transfer
• Coherent quantum transport in disordered systems: A unified polaron treatment of hopping and band-like transport
• Whats special about Y6; the working mechanism of neat Y6 organic solar cell
• Delocalised kinetic Monte Carlo for simulating delocalisation-enhanced charge and exciton transport in disordered materials
• Even a little delocalization produces large kinetic enhancements of charge-separation efficiency in organic photovoltaics
• Generalised Marcus Theory for Multi-Molecular Delocalised Charge Transfer
• Phonon-Assisted Ultrafast Charge Separation in a Realistic PCBM Aggregate
• Classification of Coherent Enhancements of Light-Harvesting Processes
• Ultrafast Charge Separation and Nongeminate Electron-Hole Recombination in Organic Photovoltaics
• Coherent and controllable enhancement of light-harvesting efficiency
• Mechanism of delocalisation-enhanced exciton transport in disordered organic semiconductors
• Environmentally improved coherent light harvesting
• Origin of space-separated charges in photoexcited organic heterojunctions on ultrafast time scales
• Jumping kinetic Monte Carlo: Fast and accurate simulations of partially delocalised charge transport in organic semiconductors