Photovoltaics
"relating to the production of electric current at the junction of two substances exposed to light", Google Dictionary
Solar energy
As fossil fuels is getting depleted, the development of renewable energy becomes the most important and urgent issue for human. Especially, solar energy has been noticed as one of the most promising renewable energy resources owing to universal availability, sustainability, and carbon-free character. Despite such outstanding features, the practical application still suffers from low solar-to-electricity efficiency. Theoretically, a single junction solar cell cannot exceed Shockely-Queisser limit (~33%). Which factor places such a low conversion efficiency on solar cell?
Solar energy
As fossil fuels is getting depleted, the development of renewable energy becomes the most important and urgent issue for human. Especially, solar energy has been noticed as one of the most promising renewable energy resources owing to universal availability, sustainability, and carbon-free character. Despite such outstanding features, the practical application still suffers from low solar-to-electricity efficiency. Theoretically, a single junction solar cell cannot exceed Shockely-Queisser limit (~33%). Which factor places such a low conversion efficiency on solar cell?
Shockley-Queisser Limit
Solar panel can only collect the photons having energy in the range of band gap. If photons contain more energy than band gap, then excessive energy would be wasted as useless heat form (red arrow in the scheme). The graph presented below confirms that the great deal of high-energy photons is wasted through a process called thermalization. The inefficient absorption of UV-Vis region's photon is one of the main causes a such low limitation on solar cell. How can we overcome Shockely-Queisser limit?
Solar panel can only collect the photons having energy in the range of band gap. If photons contain more energy than band gap, then excessive energy would be wasted as useless heat form (red arrow in the scheme). The graph presented below confirms that the great deal of high-energy photons is wasted through a process called thermalization. The inefficient absorption of UV-Vis region's photon is one of the main causes a such low limitation on solar cell. How can we overcome Shockely-Queisser limit?
Singlet Fission
Multi-exciton process has been known to chemists for half a century. Singlet fission which produces two absorbable triplet photons from one high-energy singlet photon has gained a considerable attention with aim of solar cell application. In singlet fission materials, the excessive energy is used to promote and generate another exciton instead of being wasted as heat. Also, unlike an intersystem crossing which is widely known for triplet generation pathway, singlet fission is a spin-allowed process and occurs ultrafast.
Multi-exciton process has been known to chemists for half a century. Singlet fission which produces two absorbable triplet photons from one high-energy singlet photon has gained a considerable attention with aim of solar cell application. In singlet fission materials, the excessive energy is used to promote and generate another exciton instead of being wasted as heat. Also, unlike an intersystem crossing which is widely known for triplet generation pathway, singlet fission is a spin-allowed process and occurs ultrafast.
Chemical equation and graphical description of electronic states involved in singlet fission would be like below.
Multi-Electron Transfer
The benefit of multiple exciton generation process can be realized only when more than one exciton is harvested. Recently, the simulation-led systematic design enacts multiple charge carriers extraction in singlet fission materials coupled to a multi-electron acceptor. We are actively working on understanding multi-electron transfer mechanism and designing promising pairs of singlet fission chromophore and acceptor.
The benefit of multiple exciton generation process can be realized only when more than one exciton is harvested. Recently, the simulation-led systematic design enacts multiple charge carriers extraction in singlet fission materials coupled to a multi-electron acceptor. We are actively working on understanding multi-electron transfer mechanism and designing promising pairs of singlet fission chromophore and acceptor.
Related publications
[1] Hyungjun Kim, Bradley Keller, Rosina Ho-Wu, Neranga Abeyasinghe, Ricardo J. Vázquez, Theodore Goodson III*, and Paul M. Zimmerman*, "Enacting Two-Electron Transfer from a Double-Triplet State of Intramolecular Singlet Fission", J. Am. Chem. Soc., 140, 7760 (2018)
[2] Benedetta Carlotti, Zhengxu Cai, Hyungjun Kim, Valerri Shaparov, Ifeanyi Kizito Madu, Donglin Zhao, Wei Chen, Paul M. Zimmerman, Luping Yu, and Theodore Goodson III*, "Charge Transfer and Aggregation Effects on the Performance of Planar vs. Twisted Non-Fullerene Acceptor Isomers for Organic Solar Cells", Chem. Mater., 30, 4263 (2018)
[3] Hyungjun Kim, Theodore Goodson III, and Paul M. Zimmerman*, “Density Functional Physicality in Electronic Coupling Estimation: Benchmarks and Error Analysis”, J. Phys. Chem. Lett., 8, 3242 (2017)
[1] Hyungjun Kim, Bradley Keller, Rosina Ho-Wu, Neranga Abeyasinghe, Ricardo J. Vázquez, Theodore Goodson III*, and Paul M. Zimmerman*, "Enacting Two-Electron Transfer from a Double-Triplet State of Intramolecular Singlet Fission", J. Am. Chem. Soc., 140, 7760 (2018)
[2] Benedetta Carlotti, Zhengxu Cai, Hyungjun Kim, Valerri Shaparov, Ifeanyi Kizito Madu, Donglin Zhao, Wei Chen, Paul M. Zimmerman, Luping Yu, and Theodore Goodson III*, "Charge Transfer and Aggregation Effects on the Performance of Planar vs. Twisted Non-Fullerene Acceptor Isomers for Organic Solar Cells", Chem. Mater., 30, 4263 (2018)
[3] Hyungjun Kim, Theodore Goodson III, and Paul M. Zimmerman*, “Density Functional Physicality in Electronic Coupling Estimation: Benchmarks and Error Analysis”, J. Phys. Chem. Lett., 8, 3242 (2017)